J Leonard Dixon

Ancel Keys’ studies certainly raised concerns about the intake of a high fat and cholesterol diet on blood cholesterol concentrations and its effects on Coronary Heart Disease (CHD). As I indicated earlier, at the time of his studies the rates of CHD were much higher in the US than in Europe (except for those in East Finland), and Ancel Keys specifically acknowledged in his book that he could not explain this observation. In part 2, I discussed the introduction of margarine into the US market in the 1950s as being a possible reason for this observation. There is one other possible factor that Dr. Keys mentioned in his book published in 1980. This was that additives were included in American cigarettes that made them burn more rapidly and efficiently, allowing them to deliver higher concentrations of nicotine and other deadly chemicals to the American smoker. This was in contrast to cigarettes consumed in Europe, especially in southern Europe, that were often hand made by the smoker, and thus they burned less efficiently. Since most of the participants in the Seven Countries study were men who were smokers or ex-smokers, the difference in cigarette manufacture may have been an important factor, outside of diet or other factors such as activity, in the difference in the basic rate of CHD between the the US and European countries.

There was one other interesting factor that influenced blood cholesterol concentrations at the time of the Seven Countries study. People made coffee by using a coffee percolator, which essentially uses steam from boiling water/coffee to extract the coffee grounds. This process was extremely efficient at extracting flavors and other compounds from coffee, including a substance that was later found to increase blood LDL concentrations. I remember vividly my father making his morning coffee using a coffee percolator. Later on, drip coffee makers became more common and this process did not extract the LDL raising substance out of the coffee. This may have been another reason why blood cholesterol levels were higher in the 1950s and 60s. Therefore, the concentrations of cholesterol in blood of Americans probably fell slower in response to a lower fat and cholesterol diet than would have been predicted, because other factors, such as the consumption of margarine and drinking percolated coffee, were responsible for keeping blood cholesterol concentrations artificially high.

Dietary Guidelines and the War on Fat and Cholesterol

The studies of Ancel Keys and other researchers such as Mark Hegsted did not go unnoticed by health administrators and advocates. In 1976, the Select Committee on Nutrition and Human Needs, chaired by Senator George McGovern, held hearings on the role of diet in the development of the chronic diseases that were raging at that time. In 1977, this Congressional Select Committee issued the “Dietary Goals for the United States.” The recommendations of this report were:

Increase carbohydrate intake to 55 to 60 percent of calories

Decrease dietary fat intake to no more than 30 percent of calories, with a reduction in intake of saturated fat, and recommended approximately equivalent distributions among saturated, polyunsaturated, and monounsaturated fats to meet the 30 percent target

Decrease cholesterol intake to 300 mg per day

Decrease sugar intake to 15 percent of calories

Decrease salt intake to 3 grams per day

The problem with the 1977 Select Committee report was that they took general recommendations made by a number of health researchers and then included precise percentages for some of them, such as the ones for macronutrient intake, in the final recommendations. Increasing carbohydrate intake to 55 to 60 % of total kcal is probably too high of an intake of carbohydrates, especially if 15 -20 % of total Kcal come from simple sugars. Likewise, decreasing total fat intake to 30 % percent of total kcal intake is probably too low. We now know that the type of fat consumed is more important than the total amount of fat in the diet. But really, the recommendation of 55-60% of kcal from carbohydrates was probably unwise, and at the time, unsupported by the current knowledge.

Also, the Select committee report was from a committee in Congress and was largely written by congressional staff members. Efforts to produce recommendations from a scientific committee or agency were then engaged. In 1980, Health and Human Services and USDA released, in a combined report, “Nutrition and Your Health: Dietary Guidelines for Americans,” first edition. The recommendations in this document were more general than those in the previous “Dietary Goals” from 1977. The 1980 “Dietary Guidelines” recommended:

Eat a variety of foods

Maintain desirable weight

Avoid too much fat, saturated fat and cholesterol

Eat foods with adequate starch and fiber

Avoid too much sugar

Avoid too much salt

If you drink alcohol, do so in moderation

There were no numeric recommendations for % kcal from fat and carbohydrate.

The 1985 release of the “Dietary Guidelines for Americans,” second edition, contained almost the exact recommendations that were in the first edition from 1980. In 1989, the USDA and HHS convened a second expert committee to review the 1985 edition of the “Dietary Guidelines.” In 1990 this panel released the third edition of the “Dietary Guidelines,” and this version contained numerical recommendations for the % intake of total fat and saturated fat. Again, the recommendation was that total fat should make up 30% or less of total kcal, and that saturated fat should make up less then 10% of total kcal intake. If fat contributes only 30 % of kcal, and protein contributes about 15-20% of kcal, this recommendation implied that carbohydrates should contribute about 50-55% of kcal to the diet. The basic question here is, was it correct to recommend that the American public should consume 50 % of their kcal, or more, in the form of carbohydrate?

The recommendations on macronutrient percentages and what types of fat to eat were still somewhat immature at this time (1970s to 1980s). Health experts were still basing their recommendations on the outcome of Ancel Keys’ Seven Countries study and other short term dietary intake studies. As discussed previously, deaths due to CVD in the 1950s and 1960s were due to a number of causes, including the consumption of trans fats in addition to the consumption of saturated fat, the smoking of efficient, toxic cigarettes, and possibly, the drinking of coffee made with a percolator.   Additionally, Americans were becoming increasing inactive.

To answer this question, let’s consider an evolutionary argument concerning what percent of total kcal intake should come from fat and carbohydrates in humans.

Studies of various and diverse cultures have shown that humans, throughout evolution, consumed a wide range of diets with different macronutrient make-ups. This last point was wonderfully illustrated in a recent article by Leonard (   ).

Below is a table extracted from this article.

The upper values for percent macronutrient content of the diet are values taken from selected studies of hunter-gatherers and studies of pastoral and small, basic agricultural societies. The lower data are values for the intakes of Americans (an industrial society) from the 1950s to current time. The percent kcal from protein is, for the most part, higher in subsistence-level and simple agricultural humans than in the American diet. The values for percent kcal from carbohydrates and fat are quite varied. This shows that humans can adapt and utilize diets with differing levels of these macronutrients. As eloquently stated by Dr. Leonard, “This ability to utilize a diverse array of plant and animal resources for food is one of the features that allowed Humans to spread and colonize ecosystems all over the world.”

The lower values for Americans show an interesting trend. In the 1950s the intake of fat was relatively high (approximately 45%), and then it decreased during the last decades of the 20th century in response to recommendations by various health authorities and the published “Dietary Guidelines.” Finally the percent of kcal from fat is currently increasing due to relaxation of the impact from fat phobia and due to the beliefs of many that a high carbohydrate is not healthy either.

However, the take home points from Dr. Leonard’s article are that the actual percentages of the different macronutrients are not as important as the composition of each of these components. Human populations can live over a wide range of macronutrient intakes, but as we will discuss later, the content of the individual components in each category are extremely important.

Going back to the original McGovern “Dietary Goals” (1977), it was recommended that Americans “Decrease sugar intake to 15 percent of calories.” Additionally, the first edition of the “Dietary Guidelines,” (1980) recommended, “Avoid too much sugar.” Therefore, these very general recommendations were correct for some of their recommendations concerning carbohydrate intake. However, the food companies increased the amount of sugar in their products, and of course, Americans consumed these foods in ever increasing amounts.

Conclusion

In conclusion, although the different Dietary recommendations made starting in 1977 could have been more prudent, in no way can they be blamed for starting the Obesity epidemic.