01 September 2012

Nutritional Science - or the lack of it

Today's post is about bad science, and why we came to believe that dietary fat is the cause of heart disease. (A brief history here.)
"Ancel Keys deserves the lion's share of credit for convincing us that cholesterol levels predict heart disease and that dietary fat is a killer."
                                                                        - Gary Taubes
In 1951, Ancel Keys was invited to a conference in Naples (Italy). He came to realize that the poor in this area were relatively free from heart disease, but not the rich. After taking a closer look at their diet, he noted that the poor ate little meat and the rich had a diet high in fat:
" The pasta was loaded with meat sauce and everyone added heaps of parmesan cheese. Roast beef was the main course. Dessert was a choice of ice cream or pastry."
This experience was enough to convince Ancel Keys that dietary fat is the main culprit of heart disease. In order to find further evidence to support this hypothesis, Keys traveled around the world to assess the fat content of different diets and people's health.

In 1956, he launched the Seven Countries Study. The results were published in 1970. At that time, data for saturated fat content in the diet and deaths from heart disease, was available from 22 countries. However, Keys only picked the countries which supported his theory, he simply ignored the others where his theory could not explain the observations. A very good example is France: high saturated fat in the diet and relatively low incidence of heart disease. If he had chosen this country as well, there might be no such thing as the "French Paradox".

Keys also noticed that during war times, when food rationing was implemented, death from coronary heart disease virtually disappeared. He concluded that this dramatic decrease was due to the low fat content of the diet (less meat, eggs, diary products). On a side note: during war times, other food items were also rationed, like flour and sugar. But Keys remained focused on the fat content of the diet.

Many researchers would not accept this theory. In 1957, the AHA (American Heart Association) concluded that Keys' evidence was insufficient. 
"There is not enough evidence available to permit a rigid stand on what the relationship is between nutrition, particularly the fat content of the diet, and atherosclerosis and coronary heart disease."
However only a few years later, in 1960, the AHA (Keys was part of the committee) issued a report stating that Keys' theory was supported "by the best scientific evidence of the time". This theory was accepted by the government and was the start of the low fat nutritional advice still alive today.

Skepticals argued that Keys' theory failed to "explain the absence of [...] chronic diseases in cultures whose traditional diets contained predominantly fat and protein and little or no plant foods and thus little or no fiber - the Masai, the Samburu, the Native Americans of the Great Plains, the Inuit." (- Gary Taubes). But the 13th January 1961 cover story article of the TIME magazine launched the mainstream opinion still prevalent today. This article was more than 4 pages long explaining that saturated fat causes heart disease. There was only a little mention that Keys' hypothesis is "still questioned by some research with conflicting ideas of what causes coronary heart disease".

When a diet low in fat became the government diet of choice to be recommended to the population, researchers knew that in order to get funding for their research, they needed to support the government's theory. Many researchers still skeptical to Keys hypothesis were simply discredited and forgotten. A very good example is John Yudkin (I briefly mentioned him already here).

Yudkin supported the theory that it was the appearance of high amounts of sugar which was the cause of diseases of civilization, rather than the saturated fat in our diet. Yudkin retired in 1971 and a year later, published his book "Pure, White and Deadly". He was discredited for having supported a different theory. Everybody else who did the same and talked about it publicly, endangered their reputation.

Low fat products are still "fashionable" today on the market, and our diet is more and more based on carbohydrates. However, the number of chronic diseases is still in increase. There must be something wrong more with Keys' theory, rather than the evidence that refutes it.

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