The laws of thermodynamics do not imply causation There is no direction of causation in the principle of energy conservation. This brilliant idea dates back to Hugo Rony’s Obesity and Leanness (1940) and it has been resurrected by Gary Taubes in The Diet Delusion (2007). Taubes uses the example that a teenage boy gains weight not because he is overeating and sedentary. He eats and sleeps all the time because he is growing and the growth hormone is driving his energy intake and expenditure and weight gain is but a result of this. The implications of this concept for the treatment of obesity are significant. To solve something, you need to know what has caused it. It is universally assumed, in the world of dieting, that overweight people have eaten too much and/or not done enough activity. Hence the prescribed solution is to eat less/do more. Notwithstanding the fact that weight gain is about fat stored, and not just energy in and out, if there is a separate factor, which has caused the person to eat in a way such that fat can be stored, this separate factor is a cause and needs to be addressed. Over 25 years ago, we had already questioned even an association between overweight people, food consumption and exercise. The 1983 Royal College of Physicians report on Obesity states: “The traditional view that the majority of overweight subjects are eating more or exercising less than those of a normal weight is now recognised as not being uniformly true.” We missed an opportunity to build on this observation and look at what was going on within the body, rather than spending another quarter of a century obsessing with calories in and calories out. Even if we did observe an association between, let’s say, being overweight and doing less, we must be open to the idea that (quite logically) people are not, for example, overweight because they are sedentary, but they are sedentary because they are overweight (a larger frame is quite simply more difficult to move around). This then leads the researcher to look at sedentary behaviour as an effect and not a cause. (There is likely an element of both, of course, but I am making the point that we have assumed only one direction of causation. Rare and useful are the studies that assert “Fatness leads to inactivity, but inactivity does not lead to fatness.”)
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