Yudkin completed his medical studies in 1938, and was appointed Director of Medical Studies at Christ's College. The same year, he started research at the
Dunn Nutritional Laboratory in Cambridge, working principally on the effects of dietary
vitamins. His studies of the nutritional status of school children in Cambridge showed that supplementation of the diet with vitamins had little effect on their general health. The studies also showed serendipitously that children from a poorer area of Cambridge were shorter and lighter, and had lower
haemoglobin levels and a weaker grip, than those from a wealthier area. Moreover, children from three industrial towns in Scotland were, on average, inferior in the same four measurements to the average Cambridge child, and the children from the poorer families in the Scottish towns were inferior in these measurements to those from the wealthier families. These findings probably helped to persuade Yudkin that nutrition was not only a biological science but also had important social and economic components and implications. In 1942 he wrote an article in
The Times (published anonymously, as was customary in those days) pointing out that there were a large number of organisations in the UK concerned in some way with nutrition – the Ministry of Food, the Ministry of Health, the Medical Research Council, the Cabinet Advisory Board on Food Policy, etc. – but no single body responsible for formulating a uniform plan for nutrition. What was needed was a UK Nutrition Council with oversight of food policy. During the Second World War, Yudkin served in the
Royal Army Medical Corps and was posted to
Sierra Leone. While there he studied a skin disease that was prevalent among local African soldiers and discovered that it was due not to an infection, as had been believed, but to
riboflavin deficiency. He found that the Army had devised a uniform diet for its soldiers in the four British West African colonies (Gambia, Sierra Leone, Gold Coast and Nigeria). This diet was, on paper, adequate in all nutrients – including riboflavin, which was supplied predominantly from millet. But it turned out that millet, although a staple in the Gold Coast and Nigeria, was loathed by soldiers from Sierra Leone, who would not eat it even if they were hungry. In 1945, shortly after the end of the war, he was elected to the Chair of Physiology at
Queen Elizabeth College in London (then the King's College of Household and Social Science). Over the next several years, under his leadership, the college and the
University of London established a BSc degree in nutrition nutrition and
public health,
diseases of affluence, food choice both in human beings and in experimental animals, and historical aspects of the human diet. But his concern became increasingly focused on two topics: the treatment of overweight and the harmful effects of excessive sugar (
sucrose) consumption. The end of food rationing early in the 1950s brought with it an increase in the number of people who were suffering from
obesity, and by 1958 slimming diets had proliferated, many of them with no scientific basis. Yudkin showed that in most patients weight could be well controlled by restricting dietary
carbohydrate.
This Slimming Business (1958), which expressed this idea in user-friendly language, proved popular: it was republished in paperback in 1962, reached its fourth edition in 1974, reappeared as
Lose Weight, Feel Great in the US, was translated into Dutch and Hungarian, and spawned ''The Slimmer's Cook Book
in 1961 and The Complete Slimmer'' in 1964. Yudkin's interest in sugar arose indirectly from his studies of the alarming increase in many countries during the first half of the twentieth century in the incidence of
coronary thrombosis. This increase was of great concern to health professionals, and it was widely attributed to an increase in the amount of fat, or of a particular type of fat, in the diet. In a paper published in 1957 Yudkin analysed diets and coronary mortality in different countries for the year 1952, and also analysed trends in diet, and trends in coronary mortality, in the UK between 1928 and 1954. The first of these analyses produced no evidence for the view that total fat, or
animal fat, or
hydrogenated fat, was the direct cause of coronary thrombosis; in fact the closest relationship between coronary deaths and any single dietary factor was with sugar. The second analysis, that of historical trends in the UK, found no good relationship with any single dietary factor. Instead, it suggested that some change or changes in lifestyle during the past several decades was contributing to the increased incidence of coronary deaths. One obvious change was reduced exercise, and another was alterations in diet. Given the dramatic increase in sugar consumption during the first half of the century, Yudkin started to suspect that excessive sugar in the diet might contribute not only to obesity but also to
coronary heart disease. Studying historical data from many different countries, he found that increasing prosperity leads to an increase in sugar consumption, particularly in manufactured foods, and also that the ready availability of sugar-containing manufactured foods even in the poorer countries may lead to their being bought in preference to more nutritious food. In 1964 he wrote 'In the wealthier countries, there is evidence that sugar and sugar-containing foods contribute to several diseases, including
obesity,
dental caries,
diabetes mellitus and
myocardial infarction [heart attack]'. An obstacle to the acceptance of these ideas was the belief at the time that sugar and starch were metabolised in the same way, so that one would expect no difference in their effects. Yudkin and his associates, however, fed both experimental animals and human volunteers with differing quantities of sugar and starch, and found major differences between the two carbohydrates in their metabolic effects. Unlike his colleague
Thomas L. Cleave, Yudkin believed sugar was more harmful than refined grains and refused to use the term "refined carbohydrates" because it gave "the impression that white flour has the same ill effects as sugar". As early as 1967 Yudkin suggested that the excessive consumption of sugar might result in a disturbance in the secretion of insulin, and that this in turn might contribute to atherosclerosis and diabetes. ==
Pure, White and Deadly ==