In 1938 he joined the Dunn Nutrition Laboratory where he undertook research into vitamin A and riboflavin, and where his interest in the effect of socioeconomic factors on nutrition took form. During World War II he served as a physiologist in West Africa. In 1945 he was appointed Professor of Physiology at the University of London. After 8 years he succeeded in establishing the first university department in the UK that taught nutrition at undergraduate level. In the 1950's he went against the hypothesis that coronary heart disease is caused by intake of fat. In one of his popular books he recommended cutting out less nutritious elements – carbohydrates – and in 1957 he convincingly claimed that heart disease is partly rooted in the combination of little physical exercise and over eating. In the 60's he emphasized the virtues of eating meat and dairy products and the disadvantages of the massive sugar consumption in Western diet. This brought him funds from the dairy industry on the one hand, but also brought attacks from the powerful sugar lobby.
Prof. Yudkin advised the government of the young state of Israel on nutrition matters at a time when food was scarce. For many years he was an energetic governor of The Hebrew University of Jerusalem, which awarded him an honorary fellowship in 1993. Prof. John Yudkin died on July 12 1995.