“A correlation does not prove that there is a causal connection”(Tim Chico, cardiologist)
Correlation, but not causality
Armitage insists that the cholesterol theory is scientifically based. She admits, however, that it is difficult to draw direct conclusions about heart disease from nutritional studies. In randomized, controlled studies that correspond to the gold standard, saturated fats in food are replaced by polyunsaturated fatty acids, such as those found in vegetable oil. This lowers the level of LDL cholesterol in the blood. Strangely enough, this did not result in lower mortality in most studies. Many other nutritional studies that address heart disease are observational. They are based on nutrition questionnaires that participants fill out from memory and therefore have their limits. “Such approaches give a general indication of which foods are linked to heart disease,” says Tim Chico, a cardiologist at the University of Sheffield in the UK. “However, such a correlation does not prove that there is a causal relationship,” he adds.
The many contradicting findings could suggest that saturated fats have been overestimated and other food components that contribute to the development of heart disease may have been overlooked. Four years before Keys was on the cover of Time Magazine, British physiologist John Yudkin suggested that the real danger to human health was sugar. Back then, his findings were largely ignored. However, in 2016 it emerged that influential research from the 1960s that downplayed sugar’s role in coronary heart disease had been funded by the sugar industry.
Shortly after this reveal, the results of the Prospective Urban Rural Epidemiology (PURE) study suggested that a high-carbohydrate diet, rather than a high-fat diet, can drastically shorten life. The authors found no connection between high fat consumption and the occurrence of heart attacks or cardiovascular diseases. On the contrary: the study found that a diet high in saturated fatty acids reduced the risk of stroke by around 20 percent. “New data show that refined sugar, not fat, is probably the main problem in our diet,” says study leader Mahshid Dehghan, nutritionist at the Population Health Research Institute in Hamilton, Canada. However, the PURE study is also based on questionnaires and is therefore subject to the same restrictions as many other observational studies.
DuBroff would not call himself an absolute cholesterol skeptic. Ascribing all the blame to bad cholesterol, however, gives an incomplete picture at best. “To concentrate only on LDL is a gross simplification of a very complex disease process,” says the cardiologist. He points to a study co-authored by Ravnskov in which subjects with the highest LDL cholesterol levels lived longer than those with the lowest levels. Research from 2019 also suggests that levels of a certain subset of LDL may be a better early indicator of heart attacks than the total amount of LDL present. Further research needs to be done to clear up the confusion about the effects of cholesterol, says DuBroff. Other biochemical mechanisms and nutritional components could also cause heart disease, such as insulin resistance and inflammation.
Although critics questioned his life’s work, it seemed to work for Keys. He died in 2004 at the age of 100 after sticking to a Mediterranean diet for most of his life. Lots of olive oil, starchy foods and vegetables, low in saturated animal fats – Chico recommends this plan to his patients. He doesn’t think it’s bad if they want to forego pasta and also want to keep their diet low in carbohydrates. “Why does it always have to be an either-or?” He asks. “I would like a more constructive discussion about how we are addressing the multiple influences on heart disease instead of holding a popularity contest.”