Human nutrition

The Recommended Dietary Allowances (RDAs) are scientifically determined levels of essential nutrient intake, deemed sufficient by the Food and Nutrition Board to meet the nutritional needs of nearly all healthy individuals. The first RDAs were published in 1943, during World War II, with the aim of setting standards for optimal nutrition. The initial editions outlined daily nutrient recommendations for various age groups, reflecting the latest scientific insights at the time (NRC, 1943). The history and evolution of the RDAs have been extensively detailed by the chair of the first Committee on Recommended Dietary Allowances (Roberts, 1958). Over the years, the RDAs have been periodically updated, with the current version being the tenth edition. Originally intended to address nutrition issues related to national defense, the RDAs now serve multiple roles, including guiding food supply planning for population groups, interpreting dietary intake data, establishing standards for food assistance programs, assessing the nutritional adequacy of food supplies, designing nutrition education initiatives, aiding in the development of new food products, and setting guidelines for food labeling. However, the data underpinning these nutrient requirement estimates are often limited. Dietary Reference Values (DRVs) represent the nutritional standards set by the United Kingdom's Department of Health and the European Food Safety Authority (EFSA) for assessing and planning dietary intakes. The UK's Department of Health introduced these guidelines in 1991 with the publication of Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. This document provides recommended nutrient intakes for the UK population, offering a framework for ensuring adequate nutrition. DRVs are categorized into three main types: Reference Nutrient Intake (RNI), which covers the nutritional needs of 95% of the population; Estimated Average Requirement (EAR), meeting the needs of 50%; and Lower Recommended Nutritional Intake (LRNI), which addresses the requirements of 5% of the population. These categories help to tailor dietary recommendations to different segments of the population, ensuring a more personalized approach to nutrition. == Nutrients ==

The seven major classes of nutrients are carbohydrates, fats, fiber, minerals, proteins, vitamins, and water. The macronutrients (excluding fiber and water) provide structural material (amino acids from which proteins are built, and lipids from which cell membranes and some signaling molecules are built), and energy. Some of the structural material can also be used to generate energy internally, and in either case it is measured in joules or kilocalories (often called "Calories" and written with a capital 'C' to distinguish them from little 'c' calories). Carbohydrates and proteins provide 17 kJ approximately (4 kcal) of energy per gram, while fats provide 37 kJ (9 kcal) per gram. However, the net energy derived from the macronutrients depends on such factors as absorption and digestive effort, which vary substantially from instance to instance. Vitamins, minerals, fiber, and water do not provide energy, but are required for other reasons. A third class of dietary material, fiber (i.e., nondigestible material such as cellulose), seems also to be required, for both mechanical and biochemical reasons, though the exact reasons remain unclear. For all age groups, males on average need to consume higher amounts of macronutrients than females. In general, intakes increase with age until the second or third decade of life. Some nutrients can be stored – the fat-soluble vitamins – while others are required more or less continuously. Poor health can be caused by a lack of required nutrients, or for some vitamins and minerals, too much of a required nutrient. Essential nutrients cannot be synthesized by the body, and must be obtained from food. Molecules of carbohydrates and fats consist of carbon, hydrogen, and oxygen atoms. Carbohydrates range from simple monosaccharides (glucose, fructose, galactose) to complex polysaccharides (starch, glycogen). Fats are triglycerides, made of assorted fatty acid monomers bound to a glycerol backbone. Some fatty acids, but not all, are essential in the diet: they cannot be synthesized in the body. Protein molecules contain nitrogen atoms in addition to carbon, oxygen, and hydrogen. The fundamental components of protein are nitrogen-containing amino acids, some of which are essential in the sense that humans cannot make them internally. Some of the amino acids can be converted (with the expenditure of energy) to glucose and can be used for energy production just as ordinary glucose, in a process known as gluconeogenesis. By breaking down existing protein, some glucose can be produced internally; the remaining amino acids are discarded, primarily as urea in urine. This occurs naturally when atrophy takes place, or during periods of starvation. Carbohydrates products: rich sources of complex and simple carbohydrates Carbohydrates may be classified as monosaccharides, disaccharides or polysaccharides depending on the number of monomer (sugar) units they contain. They are a diverse group of substances, with a range of chemical, physical and physiological properties. They make up a large part of foods such as rice, noodles, bread, and other grain-based products, but they are not an essential nutrient, meaning a human does not need to eat carbohydrates. Monosaccharides contain one sugar unit, disaccharides two, and polysaccharides three or more. Monosaccharides include glucose, fructose and galactose. Disaccharides include sucrose, lactose, and maltose; purified sucrose, for instance, is used as table sugar. Polysaccharides, which include starch and glycogen, are often referred to as 'complex' carbohydrates because they are typically long multiple-branched chains of sugar units. Traditionally, simple carbohydrates were believed to be absorbed quickly, and therefore raise blood-glucose levels more rapidly than complex carbohydrates. This is inaccurate. Some simple carbohydrates (e.g., fructose) follow different metabolic pathways (e.g., fructolysis) that result in only a partial catabolism to glucose, while, in essence, many complex carbohydrates may be digested at the same rate as simple carbohydrates. The World Health Organization recommends that added sugars should represent no more than 10% of total energy intake. The most common plant carbohydrate nutrient starch varies in its absorption. Starches have been classified as rapidly digestible starch, slowly digestible starch and resistant starch. Starches in plants are resistant to digestion (resistant starch), but cooking the starch in the presence of water can break down the starch granule and releases the glucose chains, making them more easily digestible by human digestive enzymes. Historically, food was less processed and starches were contained within the food matrix, making them less digestible. Modern food processing has shifted carbohydrate consumption from less digestible and resistant starch to much more rapidly digestible starch. For instance, the resistant starch content of a traditional African diet was 38 grams/day. The resistant starch consumption from countries with high starch intakes has been estimated to be 30-40 grams/day. In contrast, the average consumption of resistant starch in the United States was estimated to be 4.9 grams/day (range 2.8-7.9 grams of resistant starch/day). Fat A molecule of dietary fat typically consists of several fatty acids (containing long chains of carbon and hydrogen atoms), bonded to a glycerol. They are typically found as triglycerides (three fatty acids attached to one glycerol backbone). Fats may be classified as saturated or unsaturated depending on the chemical structure of the fatty acids involved. Saturated fats have all of the carbon atoms in their fatty acid chains bonded to hydrogen atoms, whereas unsaturated fats have some of these carbon atoms double-bonded, so their molecules have relatively fewer hydrogen atoms than a saturated fatty acid of the same length. Unsaturated fats may be further classified as monounsaturated (one double-bond) or polyunsaturated (many double-bonds). Furthermore, depending on the location of the double-bond in the fatty acid chain, unsaturated fatty acids are classified as omega-3 or omega-6 fatty acids. Trans fats are a type of unsaturated fat with trans-isomer bonds; these are rare in nature and in foods from natural sources; they are typically created in an industrial process called (partial) hydrogenation. There are nine kilocalories in each gram of fat. Fatty acids such as conjugated linoleic acid, catalpic acid, eleostearic acid and punicic acid, in addition to providing energy, represent potent immune modulatory molecules. Saturated fats (typically from animal sources) have been a staple in many world cultures for millennia. Unsaturated fats (e. g., vegetable oil) are considered healthier, while trans fats are to be avoided. Saturated and some trans fats are typically solid at room temperature (such as butter or lard), while unsaturated fats are typically liquids (such as olive oil or flaxseed oil). Trans fats are very rare in nature, and have been shown to be highly detrimental to human health, but have properties useful in the food processing industry, such as rancidity resistance. Essential fatty acids Most fatty acids are non-essential, meaning the body can produce them as needed, generally from other fatty acids and always by expending energy to do so. However, in humans, at least two fatty acids are essential and must be included in the diet. An appropriate balance of essential fatty acids—omega-3 and omega-6 fatty acids—seems also important for health, although definitive experimental demonstration has been elusive. Both of these "omega" long-chain polyunsaturated fatty acids are substrates for a class of eicosanoids known as prostaglandins, which have roles throughout the human body. An appropriately balanced intake of omega-3 and omega-6 partly determines the relative production of different prostaglandins. In industrialized societies, people typically consume large amounts of processed vegetable oils, which have reduced amounts of the essential fatty acids along with too much of omega-6 fatty acids relative to omega-3 fatty acids. The conversion rate of omega-6 DGLA to AA largely determines the production of the prostaglandins PGE1 and PGE2. Omega-3 EPA prevents AA from being released from membranes, thereby skewing prostaglandin balance away from pro-inflammatory PGE2 (made from AA) toward anti-inflammatory PGE1 (made from DGLA). The conversion (desaturation) of DGLA to AA is controlled by the enzyme delta-5-desaturase, which in turn is controlled by hormones such as insulin (up-regulation) and glucagon (down-regulation). Fiber Dietary fiber is a carbohydrate, specifically a polysaccharide, which is incompletely absorbed in humans and in some animals. Fiber slows down the absorption of sugar in the gut. The microbiome converts fiber into signals that stimulate gut hormones, which in turn control how quickly the stomach empties, regulate blood sugar levels, and influence feelings of hunger. Like all carbohydrates, when fiber is digested, it can produce four calories (kilocalories) of energy per gram, but in most circumstances, it accounts for less than that because of its limited absorption and digestibility. The two subcategories are insoluble and soluble fiber. ;Insoluble dietary fiber :Includes cellulose, a large carbohydrate polymer that is indigestible by humans, because humans do not have the required enzymes to break it down, and the human digestive system does not harbor enough of the types of microbes that can do so. :Includes resistant starch, an insoluble starch that resists digestion either because it is protected by a shell or food matrix (Type 1 resistant starch, RS1), maintains the natural starch granule (Type 2 resistant starch, RS2), is retrograded and partially crystallized (Type 3 resistant starch, RS3), has been chemically modified (Type 4 resistant starch, RS4) or has complexed with a lipid (Type 5 resistant starch, RS5). Whole grains, beans, and other legumes, fruits (especially plums, prunes, and figs), and vegetables are good sources of dietary fiber. Fiber has three primary mechanisms, which in general determine their health impact: bulking, viscosity and fermentation. Fiber provides bulk to the intestinal contents, and insoluble fiber facilitates peristalsis – the rhythmic muscular contractions of the intestines which move contents along the digestive tract. Some soluble and insoluble fibers produce a solution of high viscosity; this is essentially a gel, which slows the movement of food through the intestines. Fermentable fibers are used as food by the microbiome, mildly increasing bulk, and producing short-chain fatty acids and other metabolites, including vitamins, hormones, and glucose. One of these metabolites, butyrate, is important as an energy source for colon cells, and may improve metabolic syndrome. In 2016, the U.S. FDA approved a qualified health claim stating that resistant starch might reduce the risk of type 2 diabetes, but with qualifying language for product labels that only limited scientific evidence exists to support this claim. The FDA requires specific labeling language, such as the guideline concerning resistant starch: "High-amylose maize resistant starch may reduce the risk of type 2 diabetes. FDA has concluded that there is limited scientific evidence for this claim." Amino acids , a protein found in muscles. Proteins are the basis of many animal body structures (e.g. muscles, skin, and hair) and form the enzymes that control chemical reactions throughout the body. Each protein molecule is composed of amino acids which contain nitrogen and sometimes sulphur (these components are responsible for the distinctive smell of burning protein, such as the keratin in hair). The body requires amino acids to produce new proteins (protein retention) and to replace damaged proteins (maintenance). Amino acids are soluble in the digestive juices within the small intestine, where they are absorbed into the blood. Once absorbed, they cannot be stored in the body, so they are either metabolized as required or excreted in the urine. Proteins consist of amino acids in different proportions. The most important aspect and defining characteristic of protein from a nutritional standpoint is its amino acid composition. For all animals, some amino acids are essential (an animal cannot produce them internally so they must be eaten) and some are non-essential (the animal can produce them from other nitrogen-containing compounds). About twenty amino acids are found in the human body, and about ten of these are essential. The synthesis of some amino acids can be limited under special pathophysiological conditions, such as prematurity in the infant or individuals in severe catabolic distress, and those are called conditionally essential. Excess amino acids from protein can be converted into glucose and used for fuel through a process called gluconeogenesis. There is an ongoing debate about the differences in nutritional quality and adequacy of protein from vegan, vegetarian and animal sources, though many studies and institutions have found that a well-planned vegan or vegetarian diet contains enough high-quality protein to support the protein requirements of both sedentary and active people at all stages of life. Water pump in China Water is excreted from the body in multiple forms; including urine and feces, sweating, and by water vapour in the exhaled breath. Therefore, it is necessary to adequately rehydrate to replace lost fluids. Early recommendations for the quantity of water required for maintenance of good health suggested that six to eight glasses of water daily is the minimum to maintain proper hydration. However, the notion that a person should consume eight glasses of water per day cannot be traced to a credible scientific source. The original water intake recommendation in 1945 by the Food and Nutrition Board of the National Research Council read: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods." More recent comparisons of well-known recommendations on fluid intake have revealed large discrepancies in the volumes of water we need to consume for good health. Therefore, to help standardize guidelines, recommendations for water consumption are included in two recent European Food Safety Authority (EFSA) documents (2010): (i) Food-based dietary guidelines and (ii) Dietary reference values for water or adequate daily intakes (ADI). These specifications were provided by calculating adequate intakes from measured intakes in populations of individuals with "desirable osmolarity values of urine and desirable water volumes per energy unit consumed". Water content varies depending on the type of food consumed, with fruit and vegetables containing more than cereals, for example. These values are estimated using country-specific food balance sheets published by the Food and Agriculture Organisation of the United Nations. Minerals Dietary minerals are inorganic chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen that are present in nearly all organic molecules. Some have roles as cofactors, while others are electrolytes. The term "mineral" is archaic, since the intent is to describe simply the less common elements in the diet. Some are heavier than the four just mentioned – including several metals, which often occur as ions in the body. Some dietitians recommend that these be supplied from foods in which they occur naturally, or at least as complex compounds, or sometimes even from natural inorganic sources (such as calcium carbonate from ground oyster shells). Some are absorbed much more readily in the ionic forms found in such sources. On the other hand, minerals are often artificially added to the diet as supplements; the most well-known is likely iodine in iodized salt which prevents goiter. Macrominerals Elements with recommended dietary allowance (RDA) greater than 150 mg/day are, in alphabetical order: • Calcium (Ca2+) is vital to the health of the muscular, circulatory, and digestive systems; is indispensable to the building of bone; and supports the synthesis and function of blood cells. For example, calcium is used to regulate the contraction of muscles, nerve conduction, and the clotting of blood. It can play this role because the Ca2+ ion forms stable coordination complexes with many organic compounds, especially proteins; it also forms compounds with a wide range of solubility, enabling the formation of the skeleton. Food sources include yogurt, milk, cheese, leafy greens, tofu, and fortified beverages. • Chlorine as chloride ions; electrolyte; see sodium, below. • Magnesium, required for processing ATP and related reactions (builds bone, causes strong peristalsis, increases flexibility, increases alkalinity). Approximately 50% is in bone, the remaining 50% is almost all inside body cells, with only about 1% located in extracellular fluid. Food sources include oats, buckwheat, tofu, nuts, caviar, green leafy vegetables, legumes, and chocolate. • Phosphorus, required component of bones; essential for energy processing. Approximately 80% is found in the inorganic portion of bones and teeth. Phosphorus is a component of every cell, as well as important metabolites, including DNA, RNA, ATP, and phospholipids. Also important in pH regulation. It is an important electrolyte in the form of phosphate. Food sources include cheese, egg yolk, milk, meat, fish, poultry, whole-grain cereals, and many others. Sodium has a role in the etiology of hypertension demonstrated from studies showing that a reduction of table salt intake may reduce blood pressure. Trace minerals Many elements are required in smaller amounts (microgram quantities), usually because they play a catalytic role in enzymes. Some trace mineral elements (RDA 12 family of coenzymes • Copper required component of many redox enzymes, including cytochrome c oxidase (see Copper in health) • Chromium required for sugar metabolism • Iodine required not only for the biosynthesis of thyroxin, but probably, for other important organs as breast, stomach, salivary glands, thymus etc. (see Iodine deficiency); for this reason iodine is needed in larger quantities than others in this list, and sometimes classified with the macrominerals; Nowadays it is most easily found in iodized salt, but there are also natural sources such as Kombu. • Iron required for many enzymes, and for hemoglobin and some other proteins • Manganese (processing of oxygen) • Molybdenum required for xanthine oxidase and related oxidases • Selenium required for peroxidase (antioxidant proteins) • Zinc required for several enzymes such as carboxypeptidase, liver alcohol dehydrogenase, carbonic anhydrase Ultratrace minerals Ultratrace minerals are an as yet unproven aspect of human nutrition, and may be required at amounts measured in very low ranges of μg/day. Many ultratrace elements have been suggested as essential, but such claims have usually not been confirmed. Definitive evidence for efficacy comes from the characterization of a biomolecule containing the element with an identifiable and testable function. These include: • Bromine • Arsenic • Nickel • Fluorine • Boron • Lithium • Strontium • Silicon • Vanadium Vitamins Except for vitamin D, vitamins are essential nutrients, Excess levels of some vitamins are also dangerous to health. The Food and Nutrition Board of the Institute of Medicine has established Tolerable Upper Intake Levels (ULs) for seven vitamins. == Malnutrition ==

The term malnutrition addresses 3 broad groups of conditions: • Undernutrition, which includes wasting (low weight-for-height), stunting (low height-for-age) and underweight (low weight-for-age) • Micronutrient-related malnutrition, which includes micronutrient deficiencies or insufficiencies (a lack of important vitamins and minerals) or micronutrient excess • Overweight, obesity and diet-related noncommunicable diseases (such as heart disease, stroke, diabetes and some cancers). In developed countries, the diseases of malnutrition are most often associated with nutritional imbalances or excessive consumption; there are more people in the world who are malnourished due to excessive consumption. According to the United Nations World Health Organization, the greatest challenge in developing nations today is not starvation, but insufficient nutrition – the lack of nutrients necessary for the growth and maintenance of vital functions. The causes of malnutrition are directly linked to inadequate macronutrient consumption and disease, and are indirectly linked to factors like "household food security, maternal and child care, health services, and the environment". The DRI documents describe nutrient deficiency signs and symptoms. Excessive The U.S. Food and Nutrition Board sets Tolerable Upper Intake Levels (known as ULs) for vitamins and minerals when evidence is sufficient. ULs are set a safe fraction below amounts shown to cause health problems. ULs are part of Dietary Reference Intakes. Unbalanced When too much of one or more nutrients is present in the diet to the exclusion of the proper amount of other nutrients, the diet is said to be unbalanced. High calorie food ingredients such as vegetable oils, sugar and alcohol are referred to as "empty calories" because they displace from the diet foods that also contain protein, vitamins, minerals and fiber. Illnesses caused by underconsumption and overconsumption == Other substances ==

Alcohol (ethanol) Pure ethanol provides 7 calories per gram. For distilled spirits, a standard serving in the United States is 1.5 fluid ounces, which at 40% ethanol (80 proof), would be 14 grams and 98 calories. Wine and beer contain a similar range of ethanol for servings of 5 ounces and 12 ounces, respectively, but these beverages also contain non-ethanol calories. A 5-ounce serving of wine contains 100 to 130 calories. A 12-ounce serving of beer contains 95 to 200 calories. According to the U.S. Department of Agriculture, based on NHANES 2013–2014 surveys, women ages 20 and up consume on average 6.8 grams/day and men consume on average 15.5 grams/day. Ignoring the non-alcohol contribution of those beverages, the average ethanol calorie contributions are 48 and 108 cal/day. Alcoholic beverages are considered empty calorie foods because other than calories, these contribute no essential nutrients. Phytochemicals Phytochemicals such as polyphenols are compounds produced naturally in plants (phyto means "plant" in Greek). In general, the term identifies compounds that are prevalent in plant foods, but are not proven to be essential for human nutrition, as of 2018. There is no conclusive evidence in humans that polyphenols or other non-nutrient compounds from plants confer health benefits, mainly because these compounds have poor bioavailability, i.e., following ingestion, they are digested into smaller metabolites with unknown functions, then are rapidly eliminated from the body. == Intestinal microbiome ==

The intestines contain a large population of gut flora. In humans, the four dominant phyla are Bacillota, Bacteroidota, Actinomycetota, and Pseudomonadota. They are essential to digestion and are also affected by food that is consumed. Bacteria are essential for metabolizing food substrates and thereby increasing energy output, and produce a great variety of metabolites, including vitamins and short-chain fatty acids that contribute to the metabolism in a wide variety of ways. These metabolites are responsible for stimulating cell growth, repressing the growth of harmful bacteria, priming the immune system to respond only to pathogens, helping to maintain a healthy gut barrier, control gene expression by epigenetic regulation and defending against some infectious diseases. == Global nutrition challenges ==

The challenges facing global nutrition are disease, child malnutrition, obesity, and vitamin deficiency. Disease The most common non-infectious diseases worldwide, that contribute most to the global mortality rate, are cardiovascular diseases, various cancers, diabetes, and chronic respiratory problems, all of which are linked to poor nutrition. Nutrition and diet are closely associated with the leading causes of death, including cardiovascular disease and cancer. Obesity and high sodium intake can contribute to ischemic heart disease, while consumption of fruits and vegetables can decrease the risk of developing cancer. Child malnutrition According to UNICEF, in 2011, 101 million children across the globe were underweight and one in four children, 165 million, were stunted in growth. Simultaneously, there are 43 million children under five who are overweight or obese. This is because proper maternal and child nutrition has immense consequences for survival, acute and chronic disease incidence, normal growth, and economic productivity of individuals. Childhood malnutrition is common and contributes to the global burden of disease. Childhood is a particularly important time to achieve good nutrition status, because poor nutrition has the capability to lock a child in a vicious cycle of disease susceptibility and recurring sickness, which threatens cognitive and social development. The Maternal and Child Nutrition Study Group estimate that under nutrition, "including fetal growth restriction, stunting, wasting, deficiencies of vitamin A and zinc along with suboptimum breastfeeding—is a cause of 3.1 million child deaths and infant mortality, or 45% of all child deaths in 2011". Therefore, undernutrition can result in an accumulation of afflictions and health deficiencies which results in less productivity individually and as a community. However, this increase masks the discrepancies between nations, where Africa, in particular, saw a decrease in food consumption over the same years. High food prices cause consumers to have less purchasing power and to substitute more-nutritious foods with low-cost alternatives. Adult overweight and obesity Malnutrition in Industrialized nations is primarily due to non-nutritious carbohydrates sources resulting in excess caloric intake, which has contributed to the obesity epidemic affecting both developed and certain developing nations. In 2008, 35% of adults above the age of 20 years were overweight (BMI ≥ 25 kg/m2), a prevalence that has doubled worldwide between 1980 and 2008. Also 10% of men and 14% of women were obese, with a body mass index (BMI) greater than 30. There are 20 trace elements and minerals that are essential in small quantities to body function and overall human health. Globally, anemia affects 1.6 billion people, and represents a public health emergency in mothers and children under five. The World Health Organization estimates that there exists 469 million women of reproductive age and approximately 600 million preschool and school-age children worldwide who are anemic. Anemia, especially iron-deficient anemia, is a critical problem for cognitive developments in children, and its presence leads to maternal deaths and poor brain and motor development in children. Health consequences for iron deficiency in young children include increased perinatal mortality, delayed mental and physical development, negative behavioral consequences, reduced auditory and visual function, and impaired physical performance. The harm caused by iron deficiency during child development cannot be reversed and result in reduced academic performance, poor physical work capacity, and decreased productivity in adulthood. Vitamin A plays an essential role in developing the immune system in children, therefore, it is considered an essential micronutrient that can greatly affect health. The WHO estimates that 5.2 million of these children under five are affected by night blindness, which is considered clinical vitamin A deficiency. Severe vitamin A deficiency (VAD) for developing children can result in visual impairments, anemia and weakened immunity, and increase their risk of morbidity and mortality from infectious disease. This also presents a problem for women, with WHO estimating that 9.8 million women are affected by night blindness. Clinical vitamin A deficiency is particularly common among pregnant women, with prevalence rates as high as 9.8% in South-East Asia. Although salt iodization programs have reduced the prevalence of iodine deficiency, this is still a public health concern in 32 nations. Moderate deficiencies are common in Europe and Africa, and over consumption is common in the Americas. Nutrition interventions targeted at infants aged 0–5 months first encourages early initiation of breastfeeding. Exclusive breastfeeding often indicates nutritional status because infants that consume breast milk are more likely to receive all adequate nourishment and nutrients that will aid their developing body and immune system. This leaves children less likely to contract diarrheal diseases and respiratory infections. Growth failure during intrauterine conditions, associated with improper mother nutrition, can contribute to lifelong health complications. Anorexia nervosa Anorexia nervosa stands out as the psychiatric disorder with the highest mortality rate. It affects approximately 0.3% of young women and is especially common among teenage girls, with the average onset at around 15 years old. The disorder predominantly impacts females, with 80-90% of those diagnosed being women. Anorexia is the leading cause of significant weight loss in young women and is the primary reason for their admission to child and adolescent hospital services. In most cases, a clear diagnosis of weight loss driven by psychological factors can be made without resorting to a series of complex tests. Basic medical evaluations, including blood tests, electrocardiograms, and tracking the patient's weight and measurements, not only help in identifying underlying issues but also provide a reason for the patient to return for follow-up discussions. These follow-ups can often reveal psychological challenges. When weight loss is hidden, symptoms such as depression, obsessive behaviors, infertility, or amenorrhea may be the first signs that there is cause for concern. Recent research has shown no significant difference in fertility between women with a history of anorexia nervosa and those without, suggesting that despite experiencing high rates of menstrual irregularities, women with anorexia nervosa are still achieving pregnancy. Nutrition literacy The findings of the 2003 National Assessment of Adult Literacy (NAAL), conducted by the US Department of Education, provide a basis upon which to frame the nutrition literacy problem in the U.S. NAAL introduced the first-ever measure of "the degree to which individuals have the capacity to obtain, process and understand basic health information and services needed to make appropriate health decisions" – an objective of Healthy People 2010 and of which nutrition literacy might be considered an important subset. On a scale of below basic, basic, intermediate and proficient, NAAL found 13 percent of adult Americans have proficient health literacy, 44% have intermediate literacy, 29 percent have basic literacy and 14 percent have below basic health literacy. The study found that health literacy increases with education and people living below the level of poverty have lower health literacy than those above it. Another study examining the health and nutrition literacy status of residents of the lower Mississippi Delta found that 52 percent of participants had a high likelihood of limited literacy skills. While a precise comparison between the NAAL and Delta studies is difficult, primarily because of methodological differences, Zoellner et al. suggest that health literacy rates in the Mississippi Delta region are different from the U.S. general population and that they help establish the scope of the problem of health literacy among adults in the Delta region. For example, only 12 percent of study participants identified the MyPyramid graphic two years after it had been launched by the United States Department of Agriculture (USDA). The study also found significant relationships between nutrition literacy and income level and nutrition literacy and educational attainment and there is evidence that some interventions to improve health literacy have produced successful results in the primary care setting. More must be done to further our understanding of nutrition literacy specific interventions in non-primary care settings in order to achieve better health outcomes. == International food insecurity and malnutrition ==

According to UNICEF, South Asia has the highest levels of underweight children under five, followed by sub-Saharan Africans nations, with Industrialized countries and Latin nations having the lowest rates. Dietary and physical activity guidelines from the USDA are presented in the concept of a plate of food which in 2011 superseded the MyPyramid food pyramid that had replaced the Food Guide Pyramid. The United States Senate Committee on Agriculture, Nutrition, and Forestry is currently responsible for oversight of the USDA. The U.S. Department of Health and Human Services provides a sample week-long menu which fulfills the nutritional recommendations of the government. Canada Canada's Food Guide is an evidence-based education and policy tool provided by Health Canada that is designed to promote healthy eating. South Asia South Asia has the highest percentage and number of underweight children under five in the world, at approximately 78 million children. Eastern and Southern Africa The Eastern and Southern African nations have shown no improvement since 1990 in the rate of underweight children under five. Middle East and North Africa Six countries in the Middle East and North Africa region are on target to meet goals for reducing underweight children by 2015, and 12 countries have prevalence rates below 10%. However, the nutrition of children in the region as a whole has degraded for the past ten years due to the increasing portion of underweight children in three populous nations – Iraq, Sudan, and Yemen. Forty six percent of all children in Yemen are underweight, a percentage that has worsened by 4% since 1990. In Yemen, 53% of children under five are stunted and 32% are born at low birth weight. Sudan has an underweight prevalence of 41%, and the highest proportion of wasted children in the region at 16%. One percent of households in Sudan consume iodized salt. Iraq has also seen an increase in child underweight since 1990. Djibouti, Jordan, the Occupied Palestinian Territory (OPT), Oman, the Syrian Arab Republic and Tunisia are all projected to meet minimum nutrition goals, with OPT, Syrian AR, and Tunisia the fastest improving regions. This region demonstrates that undernutrition does not always improve with economic prosperity, where the United Arab Emirates, for example, despite being a wealthy nation, has similar child death rates due to malnutrition to those seen in Yemen. East Asia and the Pacific The East Asia and Pacific region has reached its goals on nutrition, in part due to the improvements contributed by China, the region's most populous country. China has reduced its underweight prevalence from 19 percent to 8 percent between 1990 and 2002. China played the largest role in the world in decreasing the rate of children under five underweight between 1990 and 2004, halving the prevalence. This reduction of underweight prevalence has aided in the lowering of the under 5 mortality rate from 49 to 31 of 1000. They also have a low birthweight rate at 4%, a rate comparable to industrialized countries, and over 90% of households receive adequate iodized salts. However, large disparities exist between children in rural and urban areas, where 5 provinces in China leave 1.5 million children iodine deficient and susceptible to diseases. Singapore, Vietnam, Malaysia, and Indonesia are all projected to reach nutrition MDGs. Singapore has the lowest under five mortality rate of any nation, besides Iceland, in the world, at 3%. Cambodia has the highest rate of child mortality in the region (141 per 1,000 live births), while still its proportion of underweight children increased by 5 percent to 45% in 2000. Further nutrient indicators show that only 12 per cent of Cambodian babies are exclusively breastfed and only 14 per cent of households consume iodized salt. Latin America and the Caribbean This region has undergone the fastest progress in decreasing poor nutrition status of children in the world. The Latin American region has reduced underweight children prevalence by 3.8% every year between 1990 and 2004, with a current rate of 7% underweight. They also have the lowest rate of child mortality in the developing world, with only 31 per 1000 deaths, and the highest iodine consumption. Cuba has seen improvement from 9 to 4 percent underweight under 5 between 1996 and 2004. The prevalence has also decreased in the Dominican Republic, Jamaica, Peru, and Chile. Chile has a rate of underweight under 5, at merely 1%. The most populous nations, Brazil and Mexico, mostly have relatively low rates of underweight under 5, with only 6% and 8%. Guatemala has the highest percentage of underweight and stunted children in the region, with rates above 45%. There are disparities amongst different populations in this region. For example, children in rural areas have twice the prevalence of underweight at 13%, compared to urban areas at 5%. == Nutrition access disparities ==

Occurring throughout the world, lack of proper nutrition is both a consequence and cause of poverty. According to UNICEF, children living in the poorest households are twice as likely to be underweight as those in the richest. Throughout the developing world, socioeconomic inequality in childhood malnutrition is more severe than in upper income brackets, regardless of the general rate of malnutrition. According to UNICEF, children in rural locations are more than twice as likely to be underweight as compared to children under five in urban areas. In the United States, the incidence of low birthweight is on the rise among all populations, but particularly among minorities. According to UNICEF, boys and girls have almost identical rates as underweight children under age 5 across the world, except in South Asia. == Nutrition policy ==

Nutrition interventions Nutrition directly influences progress towards meeting the Millennium Development Goals of eradicating hunger and poverty through health and education. Some programs have had adverse effects. One example is the "Formula for Oil" relief program in Iraq, which resulted in the replacement of breastfeeding for formula, which has negatively affected infant nutrition. They emphasized the 1000 days after birth as the prime window for effective nutrition intervention, encouraging programming that was cost-effective and showed significant cognitive improvement in populations, as well as enhanced productivity and economic growth. This document was labeled the SUN framework, and was launched by the UN General Assembly in 2010 as a road map encouraging the coherence of stakeholders like governments, academia, UN system organizations and foundations in working towards reducing under nutrition. The SUN framework has initiated a transformation in global nutrition- calling for country-based nutrition programs, increasing evidence based and cost–effective interventions, and "integrating nutrition within national strategies for gender equality, agriculture, food security, social protection, education, water supply, sanitation, and health care". Government often plays a role in implementing nutrition programs through policy. For instance, several East Asian nations have enacted legislation to increase iodization of salt to increase household consumption. Political commitment in the form of evidence-based effective national policies and programs, trained skilled community nutrition workers, and effective communication and advocacy can all work to decrease malnutrition. Market and industrial production can play a role as well. For example, in the Philippines, improved production and market availability of iodized salt increased household consumption. While most nutrition interventions are delivered directly through governments and health services, other sectors, such as agriculture, water and sanitation, and education, are vital for nutrition promotion as well. == Advice and guidance ==

Government policies Canada's Food Guide is an example of a government-run nutrition program. Produced by Health Canada, the guide advises food quantities, provides education on balanced nutrition, and promotes physical activity in accordance with government-mandated nutrient needs. Like other nutrition programs around the world, Canada's Food Guide divides nutrition into four main food groups: vegetables and fruit, grain products, milk and alternatives, and meat and alternatives. Unlike its American counterpart, the Canadian guide references and provides alternative to meat and dairy, which can be attributed to the growing vegan and vegetarian movements. In the US, nutritional standards and recommendations are established jointly by the US Department of Agriculture and US Department of Health and Human Services (HHS) and these recommendations are published as the Dietary Guidelines for Americans. Dietary and physical activity guidelines from the USDA are presented in the concept of MyPlate, which superseded the food pyramid, which replaced the Four Food Groups. The Senate committee currently responsible for oversight of the USDA is the Agriculture, Nutrition and Forestry Committee. Committee hearings are often televised on C-SPAN. The U.S. HHS provides a sample week-long menu that fulfills the nutritional recommendations of the government. Government programs Governmental organisations have been working on nutrition literacy interventions in non-primary health care settings to address the nutrition information problem in the U.S. Some programs include: The Family Nutrition Program (FNP) is a free nutrition education program serving low-income adults around the U.S. This program is funded by the Food Nutrition Service's (FNS) branch of the United States Department of Agriculture (USDA) usually through a local state academic institution that runs the program. The FNP has developed a series of tools to help families participating in the Food Stamp Program stretch their food dollar and form healthful eating habits including nutrition education. Expanded Food and Nutrition Education Program (ENFEP) is a unique program that currently operates in all 50 states and in American Samoa, Guam, Micronesia, Northern Mariana Islands, Puerto Rico, and the Virgin Islands. It is designed to assist limited-resource audiences in acquiring the knowledge, skills, attitudes, and changed behavior necessary for nutritionally sound diets, and to contribute to their personal development and the improvement of the total family diet and nutritional well-being. An example of a state initiative to promote nutrition literacy is Smart Bodies, a public-private partnership between the state's largest university system and largest health insurer, Louisiana State Agricultural Center and Blue Cross and Blue Shield of Louisiana Foundation. Launched in 2005, this program promotes lifelong healthful eating patterns and physically active lifestyles for children and their families. It is an interactive educational program designed to help prevent childhood obesity through classroom activities that teach children healthful eating habits and physical exercise. Education Nutrition is taught in schools in many countries. In England and Wales, the Personal and Social Education and Food Technology curricula include nutrition, stressing the importance of a balanced diet and teaching how to read nutrition labels on packaging. In many schools, a Nutrition class will fall within the Family and Consumer Science (FCS) or Health departments. In some American schools, students are required to take a certain number of FCS or Health related classes. Nutrition is offered at many schools, and, if it is not a class of its own, nutrition is included in other FCS or Health classes such as: Life Skills, Independent Living, Single Survival, Freshmen Connection, Health etc. In many Nutrition classes, students learn about the food groups, the food pyramid, Daily Recommended Allowances, calories, vitamins, minerals, malnutrition, physical activity, healthful food choices, portion sizes, and how to live a healthy life. A 1985 US National Research Council report entitled Nutrition Education in US Medical Schools concluded that nutrition education in medical schools was inadequate. Only 20% of the schools surveyed taught nutrition as a separate, required course. A 2006 survey found that this number had risen to 30%. Membership by physicians in leading professional nutrition societies such as the American Society for Nutrition has generally declined from the 1990s. Professional organizations In the US, Registered dietitian nutritionists (RDs or RDNs) are health professionals qualified to provide safe, evidence-based dietary advice which includes a review of what is eaten, a thorough review of nutritional health, and a personalized nutritional treatment plan through dieting. They also provide preventive and therapeutic programs at work places, schools and similar institutions. Certified Clinical Nutritionists or CCNs, are trained health professionals who also offer dietary advice on the role of nutrition in chronic disease, including possible prevention or remediation by addressing nutritional deficiencies before resorting to drugs. Government regulation especially in terms of licensing, is currently less universal for the CCN than that of RD or RDN. Another advanced Nutrition Professional is a Certified Nutrition Specialist or CNS. These Board Certified Nutritionists typically specialize in obesity and chronic disease. In order to become board certified, potential CNS candidate must pass an examination, much like Registered Dieticians. This exam covers specific domains within the health sphere including; Clinical Intervention and Human Health. The National Board of Physician Nutrition Specialists offers board certification for physicians practicing nutrition medicine. == Nutrition for special populations ==

Sports nutrition The protein requirement for each individual differs, as do opinions about whether and to what extent physically active people require more protein. The 2005 Recommended Dietary Allowances (RDA), aimed at the general healthy adult population, provide for an intake of 0.8 grams of protein per kilogram of body weight. The main fuel used by the body during exercise is carbohydrates, which is stored in muscle as glycogen – a form of sugar. During exercise, muscle glycogen reserves can be used up, especially when activities last longer than 90 min. Maternal nutrition Maternal nutrition is crucial during pregnancy and the child's first 1,000 days of life, encompassing the period from conception to the second birthday. During the first six months, infants rely exclusively on breast milk, which remains nutritionally sufficient despite maternal nutritional challenges. However, the mother's overall health and diet directly impact the child's well-being. The importance of maternal nutrition is a critical influence on a child's development during this pivotal period, as supported by recent studies. The child's growth is divided into four key stages: (1) pregnancy, from conception to birth; (2) breastfeeding, from birth to six months; (3) the introduction of solid foods, from six to 12 months; and (4) the transition to a family diet after 12 months, with each stage requiring specific nutritional considerations for optimal development. Additionally, there is a significant connection between nutrition, overall health, and learning, with proper nutritional intake being vital for maintaining healthy body weight and supporting normal growth during infancy, childhood, and adolescence. Childhood dietary patterns are influenced by various factors, including feeding challenges and nutritional needs, with significant long-term consequences. During the first year, an infant's birth weight triples, and by age five, their birth length doubles. Brain volume doubles within the first 12 months and triples by 36 months. To support this rapid growth, solid foods are introduced after six months to supplement breast milk or infant formula. As children begin to consume more table foods in their second year, they are exposed to the same diet as their caregivers, which, along with more complex food combinations, shapes their dietary habits by 24 months. Imbalances in diet during this critical period can lead to malnutrition, with the highest risk occurring around the time of weaning, typically at 12 months in the U.S. and later in the second year globally. As a child transitions from breast milk or formula, dairy milk often becomes a key nutritional source, making the quality of the diet essential for continued growth and development. Various feeding challenges can increase the risk of malnutrition in young children. These include individual factors like food neophobia, temperament, and sensitivity to bitter tastes, as well as family-related factors such as education, income, food insecurity, and cultural norms. Young children tend to accept foods that are familiar and routine, as preferences are shaped through repeated exposure. Successful food acceptance requires caregivers to be patient, persistent, and willing to offer previously rejected foods multiple times. However, when caregivers label their child as "picky" or selective, they often stop offering rejected foods after just 3-5 attempts, mistakenly attributing limited food acceptance to genetics rather than learned behavior. Bribing or pressuring children to eat, along with a permissive feeding style that caters to the child's preferences, can lead to food rejection. It's common for young children to experience "food jags" (repeatedly wanting the same food) and to have shifting food preferences. While some children may exhibit a strong aversion to new foods, these reactions are usually not permanent. In older adults, malnutrition is typically indicated by unintentional weight loss or a low body mass index, though hidden deficiencies, such as those involving micronutrients, are often harder to detect and frequently go unnoticed, especially in community-dwelling seniors. This is generally higher among the elderly, but has different aspects in developed and undeveloped countries. In developed countries, the most common cause of malnutrition is illness, as both acute and chronic conditions can lead to or worsen nutritional deficits. As age increases the likelihood of disease, older adults are at the highest risk for nutritional challenges or malnutrition. The causes of malnutrition are complex and multifaceted, with aging processes further contributing to its development. The concerns faced with nutritional markers for the elderly are highlighted by the prevalence and determinants of malnutrition in adults over 65, encompassing factors from age-related changes to disease-related risks. The challenges in addressing, understanding, identifying, and treating malnutrition is key, noting that in some cases, targeted supplementation of macro- and micronutrients may be necessary when diet alone does not meet age-specific nutritional needs. Elderly Nutrition: Protein While energy needs decrease with age, the demand for protein and certain nutrients actually rises to support normal bodily functions. Deficiencies in specific nutrients are also linked to cognitive decline, a common issue among older adults. Reduced daily food intake in the elderly often leads to insufficient protein consumption, contributing to sarcopenia, a condition marked by the loss of muscle mass. Approximately 30% of those aged 60 and above, and over 50% of individuals aged 80 and older, are affected by this condition. The inability to meet protein needs exacerbates health issues, including chronic muscle wasting and bone health deterioration, leading to functional decline and frailty. To mitigate this, older adults are advised to evenly distribute protein intake across meals—breakfast, lunch, and dinner. As aging diminishes the body's ability to synthesize muscle protein, consuming adequate essential amino acids, especially leucine, is crucial. A leucine intake of at least 3 g per meal, achieved through 25-30g of high-quality protein, is necessary for effective muscle protein synthesis. Data from the National Health and Nutrition Examination Survey III indicates that the average protein intake among the elderly is 0.9g/kg of body weight per day, with half of this intake occurring at dinner. This uneven distribution can lead to sub-optimal protein synthesis and increased use of dietary amino acids for other processes like fat storage. Therefore, evenly distributing 30 g of protein throughout the day is recommended to enhance protein turnover and prevent muscle loss. Older adults, particularly those with acute or chronic illnesses, may require higher protein intake, ranging from 1.2 to 1.5g/kg per day, due to a reduced anabolic response. Some studies suggest that an intake of 1 g/kg per day is sufficient, while others recommend 1.3 to 1.73g/kg per day for better health outcomes. Research shows that muscle mass preservation is more effectively supported by animal protein, which has a higher essential amino acid content, than by plant protein. The timing of protein intake, protein source, and amino acid content are key factors in optimizing protein absorption in the elderly. This deficiency is primarily due to inadequate dietary zinc intake, compounded by factors such as poor mastication, oral health issues, medication use that interferes with absorption, and psychosocial factors that limit food intake. Additionally, epigenetic changes like DNA methylation may impair zinc transporters, leading to decreased zinc absorption as people age. Structural changes in the gut, including altered villus shape, mitochondrial changes, crypt elongation, collagen alterations, and increased cell replication time in the crypts, also significantly affect zinc absorption in the elderly. The recommended daily allowance of zinc is 11 mg for older men and 8 mg for older women, with an upper tolerable limit of 25–40 mg per day, including both dietary and supplemental sources. However, individuals over 60 often consume less than 50% of the recommended zinc intake, which is crucial for proper body function. Data from the Third Health and Nutrition Survey in the United States revealed that only 42.5% of adults over 71 years old met adequate zinc intake levels, with many suffering from zinc deficiency. To reach the upper tolerable limit of 40 mg per day, zinc intake from both food and supplements must be considered to help normalize serum zinc levels in deficient elderly individuals. Dietary sources such as seafood, poultry, red meat, beans, fortified cereals, whole grains, nuts, and dairy products are beneficial for maintaining adequate zinc levels, though absorption is higher from animal proteins than plant-based sources. The Recommended Dietary Allowance (RDA) for vitamin B12 is 0.9-2.4 μg/day, while the estimated average requirement in the U.S. and Canada is 0.7-2 μg/day. Elderly individuals with plasma vitamin B12 levels below 148 pmol/L are considered severely deficient, and those with levels between 148 and 221 pmol/L are marginally deficient. A deficiency in these B-vitamins, particularly B6, B12, and folate, is associated with elevated homocysteine levels, which increase the risk of alzheimer's disease and dementia. Increased intake of these vitamins can lower homocysteine levels and reduce the risk of these conditions. As kidney function declines with age, the conversion of vitamin D3 to its active form is impaired, exacerbating the deficiency. Serum 25(OH)D levels below 50 nmol/L are linked to muscle weakness and reduced physical function, while levels below 25-30 nmol/L increase the risk of falls and fractures. Older adults typically consume less calcium, around 600 mg/day, which heightens their susceptibility to fractures. For optimal bone health, a calcium intake of 1000–1200 mg/day is recommended, along with 800 IU/day of vitamin D3 for those with adequate sun exposure, and up to 2000 IU/day for those with limited sun exposure or obesity. However, dietary factors like phytates, oxalates, tannins, and high sodium can impair calcium absorption and retention, underscoring the need to maintain sufficient levels of both calcium and vitamin D3 through diet or supplementation to reduce the risk of pathologic fractures. The recommended daily intake of iron for both men and women is 8 mg, with an upper limit of 45 mg/day. According to the World Health Organization, hemoglobin levels below 12 g/dl in women and 13 mg/dl in men indicate anemia. Before undergoing surgery, a subject should avoid long periods of fasting. Oral feeding should be established as soon as possible after surgery. Other aspects of nutrition such as control of glucose, reduction in risk factors that causes stress-related catabolism or impairment of gastrointestinal functions, and encourage early physical activity to encourage protein synthesis and muscle functions. == History of human nutrition ==

Early human nutrition was largely determined by the availability and palatability of foods. Humans evolved as omnivorous hunter-gatherers, though the diet of humans has varied significantly depending on location and climate. The diet in the tropics tended to depend more heavily on plant foods, while the diet at higher latitudes tended more towards animal products. Analyses of postcranial and cranial remains of humans and animals from the Neolithic, along with detailed bone-modification studies, have shown that cannibalism also occurred among prehistoric humans. Agriculture developed at different times in different places, starting about 11,500 years ago, providing some cultures with a more abundant supply of grains (such as wheat, rice and maize) and potatoes; and originating staples such as bread, pasta dough, and tortillas. The domestication of animals provided some cultures with milk and dairy products. In 2020, archeological research discovered a frescoed thermopolium (a fast-food counter) in an exceptional state of preservation from 79 in Pompeii, including 2,000-year-old foods available in some of the deep terra cotta jars. Nutrition in antiquity During classical antiquity, diets consisted of simple fresh or preserved whole foods that were either locally grown or transported from neighboring areas during times of crisis. 18th century until today: food processing and nutrition Since the Industrial Revolution in the 18th and 19th century, the food processing industry has invented many technologies that both help keep foods fresh longer and alter the fresh state of food as they appear in nature. Cooling and freezing are primary technologies used to maintain freshness, whereas many more technologies have been invented to allow foods to last longer without becoming spoiled. These latter technologies include pasteurisation, autoclavation, drying, salting, and separation of various components, all of which appearing to alter the original nutritional contents of food. Pasteurisation and autoclavation (heating techniques) have no doubt improved the safety of many common foods, preventing epidemics of bacterial infection. Modern separation techniques such as milling, centrifugation, and pressing have enabled concentration of particular components of food, yielding flour, oils, juices, and so on, and even separate fatty acids, amino acids, vitamins, and minerals. Inevitably, such large-scale concentration changes the nutritional content of food, saving certain nutrients while removing others. Heating techniques may also reduce the content of many heat-labile nutrients such as certain vitamins and phytochemicals, and possibly other yet-to-be-discovered substances. Because of reduced nutritional value, processed foods are often enriched or fortified with some of the most critical nutrients (usually certain vitamins) that were lost during processing. Nonetheless, processed foods tend to have an inferior nutritional profile compared to whole, fresh foods, regarding content of both sugar and high GI starches, potassium/sodium, vitamins, fiber, and of intact, unoxidized (essential) fatty acids. In addition, processed foods often contain potentially harmful substances such as oxidized fats and trans fatty acids. A dramatic example of the effect of food processing on a population's health is the history of epidemics of beri-beri in people subsisting on polished rice. Removing the outer layer of rice by polishing it removes with it the essential vitamin thiamine, causing beri-beri. Another example is the development of scurvy among infants in the late 19th century in the United States. It turned out that the vast majority of those affected were being fed milk that had been heat-treated (as suggested by Pasteur) to control bacterial disease. Pasteurisation was effective against bacteria, but it destroyed the vitamin C. == Research of nutrition and nutritional science ==

Antiquity: Start of scientific research on nutrition lived in about 400 BC, and Galen and the understanding of nutrition followed him for centuries. Around 3000 BC the Vedic texts made mention of scientific research on nutrition. The first recorded dietary advice, carved into a Babylonian stone tablet in about 2500 BC, cautioned those with pain inside to avoid eating onions for three days. Scurvy, later found to be a vitamin C deficiency, was first described in 1500 BC in the Ebers Papyrus. According to Walter Gratzer, the study of nutrition probably began during the 6th century BC. In China, the concept of qi developed, a spirit or "wind" similar to what Western Europeans later called pneuma. Food was classified into "hot" (for example, meats, blood, ginger, and hot spices) and "cold" (green vegetables) in China, India, Malaya, and Persia. About the same time in Italy, Alcmaeon of Croton (a Greek) wrote of the importance of equilibrium between what goes in and what goes out, and warned that imbalance would result in disease marked by obesity or emaciation. Around 475 BC, Anaxagoras wrote that food is absorbed by the human body and, therefore, contains "homeomerics" (generative components), suggesting the existence of nutrients. Around 400 BC, Hippocrates, who recognized and was concerned with obesity, which may have been common in southern Europe at the time, The works that are still attributed to him, Corpus Hippocraticum, called for moderation and emphasized exercise. (The story may be legendary rather than historical.) 1st to 17th century (1st century) created the first coherent (although mistaken) theory of nutrition. Galen was physician to gladiators in Pergamon, and in Rome, physician to Marcus Aurelius and the three emperors who succeeded him. In use from his life in the 1st century AD until the 17th century, it was heresy to disagree with the teachings of Galen for 1500 years. Most of Galen's teachings were gathered and enhanced in the late 11th century by Benedictine monks at the School of Salerno in Regimen sanitatis Salernitanum, which still had users in the 17th century. Galen believed in the bodily humours of Hippocrates, and he taught that pneuma is the source of life. Four elements (earth, air, fire and water) combine into "complexion", which combines into states (the four temperaments: sanguine, phlegmatic, choleric, and melancholic). The states are made up of pairs of attributes (hot and moist, cold and moist, hot and dry, and cold and dry), which are made of four humours: blood, phlegm, green (or yellow) bile, and black bile (the bodily form of the elements). Galen thought that for a person to have gout, kidney stones, or arthritis was scandalous, which Gratzer likens to Samuel Butler's Erewhon (1872) where sickness is a crime. He was followed by piercing thought amalgamated with the era's mysticism and religion sometimes fueled by the mechanics of Newton and Galileo. Jan Baptist van Helmont, who discovered several gases such as carbon dioxide, performed the first quantitative experiment. Robert Boyle advanced chemistry. Sanctorius measured body weight. Physician Herman Boerhaave modeled the digestive process. Physiologist Albrecht von Haller worked out the difference between nerves and muscles. 18th and 19th century: Lind, Lavoisier and modern science conducted in 1747 the first controlled clinical trial in modern times, and in 1753 published Treatise on Scurvy. Sometimes forgotten during his life, James Lind, a physician in the British navy, performed the first scientific nutrition experiment in 1747. Lind discovered that lime juice saved sailors that had been at sea for years from scurvy, a deadly and painful bleeding disorder. Between 1500 and 1800, an estimated two million sailors had died of scurvy. The discovery was ignored for forty years, but after about 1850, British sailors became known as "limeys" due to the carrying and consumption of limes aboard ship. The essential vitamin C within citrus fruits would not be identified by scientists until 1932. Drawing by Madame Lavoisier (seated at right). Around 1770, Antoine Lavoisier discovered the details of metabolism, demonstrating that the oxidation of food is the source of body heat. Called the most fundamental chemical discovery of the 18th century, Lavoisier discovered the principle of conservation of mass. His ideas made the phlogiston theory of combustion obsolete. In 1790, George Fordyce recognized calcium as necessary for the survival of fowl. In the early 19th century, the elements carbon, nitrogen, hydrogen, and oxygen were recognized as the primary components of food, and methods to measure their proportions were developed. In 1816, François Magendie discovered that dogs fed only carbohydrates (sugar), fat (olive oil), and water died evidently of starvation, but dogs also fed protein survived – identifying protein as an essential dietary component. William Prout in 1827 was the first person to divide foods into carbohydrates, fat, and protein. In 1840, Justus von Liebig discovered the chemical makeup of carbohydrates (sugars), fats (fatty acids) and proteins (amino acids). During the 19th century, Jean-Baptiste Dumas and von Liebig quarrelled over their shared belief that animals get their protein directly from plants (animal and plant protein are the same and that humans do not create organic compounds). With a reputation as the leading organic chemist of his day but with no credentials in animal physiology, von Liebig grew rich making food extracts like beef bouillon and infant formula that were later found to be of questionable nutritious value. surmised that beriberi was a nutritional deficiency not an infectious disease. In the early 1880s, Kanehiro Takaki observed that Japanese sailors (whose diets consisted almost entirely of white rice) developed beriberi (or endemic neuritis, a disease causing heart problems and paralysis), but British sailors and Japanese naval officers did not. Adding various types of vegetables and meats to the diets of Japanese sailors prevented the disease. (This was not because of the increased protein as Takaki supposed, but because it introduced a few parts per million of thiamine to the diet.)). In the 1860s, Claude Bernard discovered that body fat can be synthesized from carbohydrate and protein, showing that the energy in blood glucose can be stored as fat or as glycogen. In 1896, Eugen Baumann observed iodine in thyroid glands. In 1897, Christiaan Eijkman worked with natives of Java, who also had beriberi. Eijkman observed that chickens fed the native diet of white rice developed the symptoms of beriberi but remained healthy when fed unprocessed brown rice with the outer bran intact. His assistant, Gerrit Grijns correctly identified and described the anti-beriberi substance in rice. Eijkman cured the natives by feeding them brown rice, discovering that food can cure disease. Over two decades later, nutritionists learned that the outer rice bran contains vitamin B1, also known as thiamine. Early 20th century has been called the father of modern dietetics. In the early 20th century, Carl von Voit and Max Rubner independently measured caloric energy expenditure in different species of animals, applying principles of physics in nutrition. In 1906, Edith G. Willcock and Frederick Hopkins showed that the amino acid tryptophan aids the well-being of mice but it did not assure their growth. In the middle of twelve years of attempts to isolate them, Hopkins said in a 1906 lecture that "unsuspected dietetic factors", other than calories, protein, and minerals, are needed to prevent deficiency diseases. In 1907, Stephen M. Babcock and Edwin B. Hart started the cow feeding, single-grain experiment, which took nearly four years to complete. In 1912 Casimir Funk coined the term vitamin to label a vital factor in the diet: from the words "vital" and "amine", because these unknown substances preventing scurvy, beriberi, and pellagra, and were thought then to derive from ammonia. In 1913 Elmer McCollum discovered the first vitamins, fat-soluble vitamin A and water-soluble vitamin B (in 1915; later identified as a complex of several water-soluble vitamins) and named vitamin C as the then-unknown substance preventing scurvy. Lafayette Mendel (1872–1935) and Thomas Osborne (1859–1929) also performed pioneering work on vitamins A and B. In 1919, Sir Edward Mellanby incorrectly identified rickets as a vitamin A deficiency because he could cure it in dogs with cod liver oil. In 1922, McCollum destroyed the vitamin A in cod liver oil, but found that it still cured rickets. It was synthesised the same year by Paul Karrer. Institutionalization of nutritional science in the 1950s Nutritional science as a separate, independent science discipline was institutionalized in the 1950s. At the instigation of the British physiologist John Yudkin at the University of London, the degrees Bachelor of Science and Master of Science in nutritional science were established. The first students were admitted in 1953, and in 1954 the Department of Nutrition was officially opened. In Germany, institutionalization followed in November 1956, when Hans-Diedrich Cremer was appointed to the chair for human nutrition in Giessen. Over time, seven other universities with similar institutions followed in Germany. From the 1950s to 1970s, a focus of nutritional science was on dietary fat and sugar. From the 1970s to the 1990s, attention was put on diet-related chronic diseases and supplementation. == See also ==