This is not to say that in these parts [the south] there are not people of good physique nor that in the north of India there are not many whose physique is poor. But speaking of the generality of the people, it is true that the physique of northern races of India is strikingly superior to that of southern, eastern and western races. This difference depends almost entirely on the diminishing value of the food . . . with respect to the amount and quality of proteins, the quality of the cereal grains forming the staple article of the diet, the quality and quantity of the fats, the minerals and vitamin contents, and the balance of the food as a whole.

What were the diets?
In northern India at that time grains such as wheat were eaten, usually as whole grains. Whole wheat has a high protein content,

McCarrison observed, especially when eaten freshly ground, with the grain retaining much of its high levels of minerals and vitamins. Also, in the north, the diet included milk products such as clarified butter (ghee), buttermilk and curds, as well as pulses (lentils mainly, eaten as dhal) and fresh vegetables and fruit. Meat was eaten sparingly if at all, although some groups such as the Pathans ate it in abundance.

By comparison the southern diet was based on white rice (mainly milled, polished or parboiled [often all threel, following which it was washed in many changes of water and finally boiled, reducing its nutritional value to virtually nil). Little milk protein was consumed in the south and meat was largely proscribed for religious reasons, and there was only a poor intake of vegetables and fruit.

McCarrison's experiments
Just as and longevity research is based on animals because human experiments are impossible, having made his observations amongst humans, set out to prove his thesis by applying to laboratory rats - all of which started from the same level of well-being - the various patterns of diet he had seen. Rats mature about 30 times faster than humans, making an experiment lasting 140 days equivalent to roughly 12 years in human terms.

In his first major experiment in this series he took seven different groups of the same strain of rat, with each group containing 20 rats, each having an even number of males and females, matched for body weight. They were kept in large cages under precisely the same conditions, each group being fed on a different pattern of diet, containing exactly the normal ingredients of either the Sikhs, the Pathans, Ghurkas, Mahrattas, Kanarese, Bengalis or the Madrasis. After 80 days and 140 days the animals were weighed and photographed, and their health was monitored throughout. The results proved precisely what McCarrison had anticipated, that the best diet of all was the Sikh (abundant in all nutrients) and the poorest the Madrasi (high in poor quality carbohydrate and deficient in protein and other nutrients).

This initial experiment so impressed McCarrison that he decided in future to keep his stock of rats (used for other experiments) on the Sikh diet. He had roughly 1,000 such animals to which he subsequently fed whole grain chappatis, fresh butter, sprouted pulses, raw fresh vegetables (cabbage, carrots) plus milk and water. Dry crusts were provided to keep their teeth healthy. Once a week a small amount of meat and bone was given. The rats were kept in these conditions for an average of two years - about 50 to 60 years in human terms, with young rats being taken periodically for experimental purposes and the older 1,000 being kept on the diet for breeding purposes.