The diet-heart idea: wishful thinking, impossible to refute.
Mann, Skeaff and Truswell,1 and Hu, Sacks and Willett2 list a number
of shortcomings in the trials, reviewed by Hooper et al.,3 that explain
why the dietary treatments were ineffective. No doubt, inferior studies
with negative results are prevalent, but where is the positive evidence
that justifies the dietary recommendations?
Mann, Skeaff and Truswell point to the improved outcome in the subgroup
analysis of the five prolonged trials. But in that analysis Hooper et al.
excluded the Sydney diet-heart study, where total mortality was
significantly increased, and included the Veterans Administration Trial,
that was biased by a significant higher number of heavy smokers in the
Mann, Skeaff and Truswell also claim that there is “an enormous body of
descriptive epidemiology, which supports the link between dietary fat,
cholesterol, and coronary heart disease”. There is nothing of the kind;
the accumulated epidemiology strongly contradicts such a link. Let me give
a few examples from a systematic review.4
In a study of Japanese migrants in the US the cultural upbringing was the
strongest predictor of coronary heart disease. Indeed, those who were
brought up in a non-Japanese fashion but preferred the lean Japanese food
had almost twice as often a heart attack compared with those who were
brought up in the Japanese way but preferred the fat American food.4
Masai people probably have the highest intake of animal fat in the world.
However, electrocardiographic abnormalities were far less frequent than in
Americans and raised atherosclerotic lesions were rare.4
Coronary mortality in southern India was seven times higher than in the
north and the age at death 44 against 52, although people in the north ate
19 times more fat, mostly animal fat, and also smoked much more.4
In 30 of 103 time periods in 33 countries fat intake increased along with
coronary mortality, but in 33 periods where the intake also increased,
coronary mortality was unchanged in ten and decreased in 23.4
In six case-control studies the diet of the coronary patients did not
differ significantly from that of the control individuals.4
In 21 cohort studies including more than 150,000 individuals with and
without coronary heart disease no study found an eating pattern in
accordance with the current view on the influence of dietary fat.4 Hu,
Sacks and Willett have published several studies with similar findings.
But just as is the case with Hooper et al.s analysis, these findings and
many other contradictions are always explained away with more or less
valid arguments. As Karl Popper would have said: the diet-heart idea is
unfalsifiable and should therefore be classified as non-science.
1. Mann J, Skeaff M, Truswell S. Dietary fats and prevention of
cardiovascular disease. Conclusions may have been underplayed. BMJ
2001;323:1000 . [Full text]
2. Hu FB, Sacks F, Willett WC. Dietary fats and prevention of
cardiovascular disease. Patient compliance should have been considered.
BMJ 2001;323:1000. . [Full text]
3. Hooper L, Summerbell CD, Higgins JPT, Thompson R, Capps NE, Davey Smith
G, et al. Dietary fat intake and prevention of cardiovascular disease:
systematic review. BMJ 2001; 322: 757-763. [Abstract/Full Text].
4. Ravnskov U. The questionable role of saturated and polyunsaturated
fatty acids in cardiovascular disease. J Clin Epidemiol 1998;51:443-60
Competing interests: No competing interests