The Diet DelusionBMJ 2009; 339 doi: https://doi.org/10.1136/bmj.b5604 (Published 23 December 2009) Cite this as: BMJ 2009;339:b5604
- David Colquhoun, professor of pharmacology, University College London
Few topics are more widely discussed than what we should eat to stay healthy. And there are few topics where the evidence is so lacking in quality. It is also a topic that is besieged by gurus, cranks, and supplement hucksters. Gary Taubes is a journalist—but he is quite an exceptional journalist. His book The Diet Delusion is more complete and more scholarly than most professional scientists could manage.
Obesity sounds simple. If you are fat it is because you eat too much or exercise too little, right? Well, no, it’s not as simple as that. For a start, it has been shown time and time again that low fat diets and exercise have small and temporary effects on weight. The problem with diet and health revolves round causality. The law of conservation of energy is an inevitable truth but says nothing about causality. It could imply that you get fat because you eat too much; or equally the causal arrow could point the other way and “we eat more, move less, and have less energy to expend because we are metabolically or hormonally driven to get fat.” The assumption that positive caloric balance is the cause of weight gain has predominated since the 1970s, and “this simple misconception has led to a century of misguided obesity research,” says Taubes.
At the heart of the problem is the paucity of randomised trials, which are the only way to establish causality. Those that there are have usually shown that diet does not matter as much as we are told. Taubes concludes: “It does little good to continue basing public health recommendations and dietary advice on association studies (the Framingham Heart Study and the Nurses Health Study are prominent examples) that are incapable of reliably establishing cause and effect.”
For Taubes a major villain was the US nutritionist Ancel Keys (1904-2004). His forceful advocacy of the low fat hypothesis in the early 1970s was, says Taubes, based on ignoring the many studies that did not agree with the idea.
It is quite possible that there was rather more to be said for the Atkins diet than was apparent at the time. Atkins was dismissed by the medical establishment as a quack. Taubes points out that conflict of interest cuts both ways. Atkins’s sternest critics at Harvard were funded by General Foods, Coca-Cola, and the sugar industry. It adds up to a sorry story of a conflict of vested interests and scientific vanity. Taubes’s view is that it could well be that the increase in obesity is, in part, a consequence of the recommendation of a low fat and hence high sugar diet.
It took Taubes five years to write this book, and he has nothing to sell apart from his ideas. No wonder it is so much better than a scientist can produce.
Cite this as: BMJ 2009;339:b5604
The Diet Delusion
By Gary Taubes
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