Re: Saturated fat is not the major issue
Saturated fat may not be the major issue in coronary heart disease (CHD), but it is not off the hook. In my commentary, I review some of the history of the debate and policy changes regarding diet and CHD.
In the 1960s and 1970s, there was a spirited debated in the journal literature regarding the roles of sugar and fat in the etiology of CHD. John Yudkin, a physician specializing in diabetes mellitus in London, presented the case that sugar was the most important risk factor [1-5]. Ancel Keys claimed it was dietary fat in his Seven Countries Study . His study looked at the diet of men aged 55-59 years at time of enrollment. Yudkin pointed out that Keys had carefully selected a set of countries to show that dietary fat was an important risk factor for CHD and that if the set of all countries for which dietary and CHD data were available were used in an ecological study, sweeteners would have a stronger correlation than fat [1,5]. Keys disagreed with Yudkin on the role of sugar as a risk factor for CHD . As Keys was able to argue in a more convincing manner than Yudkin, Keys largely prevailed. In 1975, another ecological study using data dietary supply data from 1963-1965 for 30 countries found sugar supply to have the highest correlation with ischemic heart disease mortality rates in 1968 or 1969 for both males and females . The Select Committee on Nutrition and Human Needs of the United States Senate largely accepted Key’s findings and recommended that overall fat consumption be reduced from 40 to 30% of the diet . However, the committee also recommended that sugar consumption be reduced from 25 to 15% of the diet. Food processors reduced the fat content of processed food and replaced it with sugar in order to maintain good flavor. This change was the beginning of the rapid rise in obesity in the United States.
My involvement with the topic came with a multi-country ecological study of CHD mortality rates for men and women of various age groups. I found that animal fat supply was significantly correlated with CHD for men, but sweeteners were for women . In a follow-on study, I found that for ischemic heart disease, milk carbohydrates had the highest statistical association for males aged 35+ and females aged 65+, while for females aged 35-64, sugar (added sweeteners) had the highest association. For CHD, had the highest association for males aged 45+ and females aged 75+, while for females 65-74, milk carbohydrates and sugar had the highest associations, and for females aged 45-64, sugar had the highest association . My finding for milk was largely consistent with that from previous ecological studies . However, I later admitted that this finding was in error . My hypothesis for a different finding for men and women was that men tend to eat more animal products while women tend to eat more sugar . My finding on sex differences for fat was supported in a later study .
When I held a press conference in 1998 to announce that sugar was a major risk factor for CHD, not only the American Sugar Association but also the American Heart Association (AHA) issued press statements dismissing my findings. I subsequently learned that the AHA was selling their seal of approval for low-fat foods. Bowing to overwhelming evidence now that sugar is an important risk factor for CHD, the AHA now recognizes sugar as a risk factor for CHD .
Despite the growing evidence and awareness of the role of sugar as an important risk factor for CHD, saturated fat cannot be ignored. For example, CHD rates in Finland were reduced by 80% since 1972 by reducing animal fat consumption . Significant reductions in CHD mortality rates in Poland were correlated with a switch from animal fats (down 23%) to vegetable fats (up 48%) between 1986-90 and 1994 .
While ecological studies can result in erroneous findings due to confounding, they are still very useful in developing hypotheses as well as providing information about the effects of diets over the entire lifetime. An ecological study of diet and disease found that animal product supply was highly correlated with incidence and mortality rates for types of cancer common in Western developed countries . A reasonable amount of the risk is likely to come from early life as observational studies of diet and cancer risk late in life generally did not confirm the findings. More recently an ecological study evaluated the contribution of sweetener supply in national diets to risk of diabetes .
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Competing interests: No competing interests