Epidemiology in modern history
Epidemiologic observations have drawn the attention of scientists for a long time, to the link between dietary change and CVD. Examples of populations with low CVD prevalence or populations where CVD are the first cause of mortality have led epidemiologists to do research on food.

This is what we called ‘Diet Heart Hypothesis’. But it is so incredibly complex that even today, we fail to come up with a definitive answer. Simple hypotheses (i.e. single-factor cause) and invalid experimental models have produced abundant literature, of which little is actually helpful.

We can however wonder about the dietary changes brought by the recent industrial transition. In the West, those changes can be qualified with three factors:

• Abundance of calories
• Abundance of carbohydrates
• Abundance of processed foods

Further to these, we should not forget about calorie expenditure. In industrialised countries, we have shifted to a sedentary lifestyle at work, in public transportation or for personal activities.


Hypothesis supported with charisma
Keys and his team then set out to study the dietary characteristics and lifestyles of different populations worldwide and compared the prevalence of coronary diseases. It was a rather large study at the time and needed significant funding.

This study addressed the issue of the heart attack epidemic that was hitting the US and other developed countries at the time. He quickly focused on diet-related risk factors, mostly because they were easier to measure, particularly through blood levels. Among macronutrients, Keys had already explored fat and the indirect measure of blood lipids via blood cholesterol.

The study would be published in a book in 1980 (Keys et al, Seven Countries. A Multivariate Analysis of Death and Coronary Heart Disease. Cambridge, MA; Harvard University Press, 1980, p381). In the meantime, Keys gets more famous, is interviewed often and in January 1961, he is on the cover of TIME Magazine.

Keys described a link in the studied cohorts between the percentage of saturated fats in the diet and the death rate by coronary events. The correlation is dependent on the number of countries studied but it is significant in the cohorts he chose.

Since there is a correlation between total blood cholesterol and the same events and since Keys highlights that saturated fats (especially palmitic acid, as it is the most common) increase blood cholesterol, a conclusion appeared.

He stated that saturated fats, including palmitic acid, are linked to coronary atheroma. Others have then bridged the gap, saying they cause coronary diseases. Obviously, all of this was not true. Inaccuracies and biases made his observations invalid.

Even Keys ended up publishing more balanced conclusions than others:

‘Our ten-year finding, and concordance with other studies, make it clear that the big three risk factors for coronary heart disease now established are age, blood pressure, and serum cholesterol. The findings about cigarette smoking as a risk factor indicate that here, too, relationships are not as simple as first supposed.’
(Seven Countries, p341)

He later became an advocate of the Mediterranean diet and kept studying it for a while. In 1975, he published How to Eat Well and Stay Well the Mediterranean Way (ed. Doubleday).


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