Several studies, notably those of Keys et al. (1958), have suggested that dietary fats are a major factor in the etiology of ischmmic heart disease. It is suggested that the liability to develop ischsmic heart disease increases with a rise in the total consumption of dietary fats, or that a higher consumption of saturated fatty acids increases this liability. On the other hand, there are several careful epidemiological studies from many countries, such as the statistical review by Yudkin (1957), which failed to find even a clear-cut correlation between fat consumption and mortality from ischemic heart disease. In India the consumption of fats (Indian Council for Medical Research, 1964) and also the pattern of diets and eating (Malhotra, 1964) differ from place to place, and a study of the geographical aspects of myocardial infarction with reference to dietary differences could, therefore, be worth while. The study reported in this paper stems from such an attempt.

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Perambur (Madras) and Alavakkot, both in South India, show the highest incidence rates for acute myocardial infarction as compared with the centres in the North, such as Ferozepur, Jhansi, or Delhi. The incidence is 7 times higher in Perambur (South India) than in Ferozepur (North India). These geographical trends are also reflected in the admissions for acute myocardial infarction expressed as a percentage of all admissions (Table I).

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Fats.

The fat consumption in the South is 8-19 times less than in the Punjab (Indian Council for Medical Research, 1964), the average daily amount in the case of railway sweepers, investigated by us, being 7 g. of seed oils, such as groundnut or sesame oil. The proportion of calories from fat is 3j per cent of a total of 2400 calories. In the North, on the other hand, average daily consumption of 75 g. mainly ghee and other milk fats and to some extent of vegetable seed oil, such as mustard oil or vanaspathi, provides 23 per cent of calories from fats out of a total of 2800 calories. In the higher income groups the daily fat intake in the North is even higher, being 70-190 g. against 10-30 g. in the South (Padmavati, 1962). Less obvious, but equally important, are the differences in the chemical composition of fats used by these disparate population groups. Milk, ghee, and fermented milk products, which are the main sources of fats in the Punjab and Rajasthan, contain a large proportion (43%') of short-chain lower fatty acids (Hilditch, 1949). The relative proportion of lower fatty acids in the seed oils, such as groundnut or sesame (gingelly) oil is much smaller; and in these the longchain oleic, linoleic, and palmitic acids are prominent (Nicholls, 1961). The degree of saturation of the fatty acids in the dietary fats of the South Indians versus North Indians also shows big differences. Thus, while the North Indians largely consume fats containing saturated fatty acids, the South Indians eat fat in which the poly-unsaturated fatty acids have a preponderance: the poly-unsaturated fatty acid content of the South Indian seed oils is 45 per cent against 2 per cent in the North Indian ghee and other milk fats (Indian Council for Medical Research, 1963).