Preventing mineral uptake Phytic acid has a strong binding affinity to
minerals such as
calcium,
magnesium,
iron,
copper, and
zinc. This results in precipitation, making the minerals unavailable for absorption in the
intestines. Phytic acids are common in the hulls of nuts, seeds, and grains and of great importance in
agriculture, animal nutrition, and in
eutrophication, due to the mineral
chelation and bound
phosphates released into the environment. Without the need to use
milling to reduce phytate (including nutrient), the amount of phytic acid is commonly reduced in
animal feeds by adding
histidine acid phosphate type of
phytases to them.
Oxalic acid and
oxalates are present in many plants and in significant amounts particularly in
rhubarb,
tea,
spinach,
parsley, and
purslane. Oxalates bind to
calcium,
magnesium and
iron, preventing their absorption in the human body.
Glucosinolates prevent the uptake of
iodine, affecting the function of the
thyroid and thus are considered
goitrogens. They are found in plants such as
broccoli,
Brussels sprouts,
cabbage,
mustard greens,
radishes, and
cauliflower. Some
trypsin inhibitors and
lectins are found in
legumes and interfere with digestion.
Lipase inhibitors interfere with enzymes, such as
human pancreatic lipase, that catalyze the hydrolysis of some
lipids, including fats. For example, the anti-obesity drug
orlistat causes a percentage of fat to pass through the digestive tract undigested.
Amylase inhibitors prevent the action of enzymes that break the
glycosidic bonds of
starches and other complex
carbohydrates, preventing the release of simple sugars and absorption by the body. Like lipase inhibitors, they have been used as a diet aid and obesity treatment. They are present in many types of beans; commercially available amylase inhibitors are extracted from white
kidney beans.
Hypoglycin A, which is contained in
lychees and
ackee fruit, blocks the fatty acid metabolism, so that the body uses its glycogen deposits for energy, which can cause
hypoglycemia, when these fruit are eaten in large quantities or as the sole diet.
Coprine found in some edible mushrooms, for example the
common inkcap, inhibits the
aldehyde dehydrogenase, which is a part of the alcohol digestive system. This can cause a buildup of the toxic
acetaldehyde. Therefore, mushrooms containing coprine should never be consumed together with alcoholic beverages.
Other Excessive intake of required nutrients can also result in them having an anti-nutrient action. Excessive intake of
dietary fiber can reduce the transit time through the intestines to such a degree that other nutrients cannot be absorbed. However, this effect is often not seen in practice and reduction of absorbed minerals can be attributed mainly to the phytic acids in fibrous food. Foods high in
calcium eaten simultaneously with foods containing
iron can decrease the absorption of iron via an unclear mechanism involving iron
transport protein h
DMT1, which calcium can inhibit.
Avidin is an antinutrient found in active form in raw
egg whites. It binds very tightly to
biotin (
vitamin B7) and can cause deficiency of B7 in animals and, in extreme cases, in humans. A widespread form of antinutrients, the
flavonoids, are a group of
polyphenolic compounds that include
tannins. These compounds
chelate metals such as iron and zinc and reduce the absorption of these nutrients, and they also inhibit digestive enzymes and may also precipitate proteins.
Saponins in plants may act like
antifeedants and can be classified as antinutrients. == Occurrence and removal ==