WHY WE GET FAT
Book review by Anthony Campbell. The review is licensed under a Creative Commons License.
This is effectively a digest of Taubes's exhaustive study of the causes of obesity, The Diet Delusion (published as Good Calories, Bad Calories in the USA). That book was long (345 pages) and included a lot of detailed physiology; this one is intended to be a practical resource for people who are thinking of putting the ideas into practice for themselves. Taubes is sure that they will benefit from doing this but he encourages his readers to think about the ideas he discusses to see if they seem sensible. He also warns them that anyone who adopts his ideas will be going counter to the received wisdom about what constitutes a healthy diet. Taubes hopes that patients will give it to their doctors with the aim of altering their opinion; I'm not sure how likely that is to happen.
The book is in two parts. Part 1 presents a summary of the evidence against the prevailing view of obesity. That view is, essentially, that we get fat because we take in more energy (more calories) than we expend, and the way to become slim is to reverse this balance, by eating less and exercising more. Taubes maintains that this idea is wrong: obesity results from a disorder of metabolism, in which the role of carbohydrates is central. Part 2 looks at the mechanisms that Taubes believes to underlie fat metabolism and accumulation; here he draws on the work of European, especially German, researchers in the first half of the twentieth century. These scientists were right, Taubes believes, but their ideas were ignored in the aftermath of the second world war.
Taubes begins by pointing out that low-calorie diets that bring about weight loss rely on producing a state of semi-starvation. This is all but impossible to maintain indefinitely, so almost everyone who loses weight in this way puts it back within a few months or years. Moreover, if you restrict the amount of food you eat, your body compensates by reducing activity
Exercise doesn't help either, he says. If you increase the amount of energy you expend you will feel more hungry and will replace the calories you lost by eating more. This doesn't mean that exercise isn't good for you; it is, but it won't make you slim. I tend to agree with this from my own experience, although there have been a few well-conducted studies that show that exercise alone can produce modest weight losses.
There is a puzzling fact, which most of us take for granted, that our weight remains much the same over long periods—years in some cases. Yet, if the current orthodox theory is right, our bodies must regulate their energy intake with extraordinary precision, since a slight increase or decrease in that intake should affect our weight. In fact, the amount of calories we eat does vary from day to day, yet the net result over time is usually neutral as regards weight gain or loss. This paradox has been remarked on by physiologists, but no generally agreed explanation exists. It does not depend on conscious choice because animals, too, maintain a constant weight.
Another surprising feature of fat deposition is that it is not the same in different parts of the body. Men and women have different distributions of fat, and there are disorders in which fat is lost completely from some parts of the body, such as the upper half, while it accumulates in large amounts elsewhere. This is obviously impossible to account for on a simple energy balance theory.
Taubes concludes Part 1 by criticising the 'psychologisation' of obesity. People who are too fat are constantly told that the reason is lack of self-control. So obesity is supposed to be a behavioural problem. Fatness is the penalty for self-indulgence, which makes it a moral issue. But what if that is wrong?
In Part 2 we get Taubes's view of the physiology of obesity. Here the reader with little background knowledge of science is going to have to work rather harder than in Part 2. The first chapter looks at eight years' research in animals (the ubiquitous laboratory rat) and concludes that it turns the conventional understanding on its head: 'obesity does not come about because gluttony and sloth make it so; only a change in the regulation of the fat tissue makes a lean animal obese.'
The main clue to understanding fat metabolism, as readers to Taubes's earlier book will know, is insulin. This hormone is released by the intake of carbohydrates, especially refined carbohydrates like sugar, and it enables the storage of fat. All this is explained clearly, with adequate but not excessive detail.
One might expect that fructose, the main type of sugar found in fruit, would be better for us than glucose, because it does not cause insulin release. It is widely used by food manufacturers because it is particularly sweet. But fructose is metabolised to fat by the liver, and the accompanying glucose in the diet ensures that the fat is stored in the fat tissues. Over some years, a high intake of fructose probably contributes to insulin resistance and to diabetes. Taubes makes the interesting point that the fruits we have had available to us for the last few hundred years are different from those we would have encountered for most of our evolutionary history; they have been selectively cultivated to be both bigger and sweeter.
We are constantly being told that dietary fat—especially saturated fat - is bad for us. Taubes shows, pretty convincingly, that this is a very considerable over-simplification of a complex question. We pay a lot of attention these days to 'good cholesterol' and 'bad cholesterol' in the blood, but this, too, is a popularised simplification. Although the widespread use of drugs (statins) to lower serum cholesterol levels has reduced the incidence of heart attacks, it does not follow that reducing cholesterol with diet, even if it can be done, will have the same effect. Statins may reduce heart attacks in a different way that has nothing to do with their cholesterol-lowering effect.
In fact, Taubes quotes some important large-scale studies of dietary modification that have failed to show any improvement in the incidence of heart disease, stroke, breast cancer, or colon cancer as a result of reducing total fat and saturated fat intake, even though the participants' serum levels of total cholesterol and 'bad' (LDL) cholesterol fell slightly.
Taubes says he is not writing a diet book, but in his final chapter he provides some suggestions for what be thinks a diet to lose weight by restricting carbohydrate should contain. He is careful to avoid promising miracles here. If you have been taking in too many carbohydrates for much of your life, you cannot expect to reverse the process immediately, and some people may not be able to do so at all. And if you are a man or woman in middle age it is unlikely that you will get back to the weight you were in your early twenties. But there is a good chance that you will lose a worthwhile amount of body fat, and, because you will not feel hungry all the time, you stand a better chance of not putting it back.
This is an important book because it has practical implications for readers. If Taubes is right, most of us should be reducing our carbohydrate intake very considerably. But is he right? His ideas certainly go counter to most (not all) contemporary advice. Most of us don't have the resources or skill to follow up his references and assess their reliability; we have to take much of this on trust. But at least he is no crank. He wants his ideas to be tested scientifically, and he is surely right in that. But it will take many years, if it ever happens, and meanwhile readers must make up their own minds on the basis of the evidence presented here. There are no easy answers in cases of this kind. But I have no doubt that Taubes has succeeded in showing that the present orthodox view of diet has serious flaws and has been arrived at by ignoring a great number of important scientific studies carried out in earlier years.
Scientifically minded readers will certainly want to read the earlier book, The Diet Delusion, but even those with a background in the relevant science would probably benefit from reading this one first, since familiarity with the ideas discussed here would make the detailed arguments in the larger study easier to follow.
Bad marks for the publisher: for some extraordinary reason, the physical pages are of uneven width, which makes the outer edge of the book rough; it is impossible to flutter through it with one's thumb. Most annoying.
31 January 2011
%T Why We Get Fat
%A Gary Taubes
%I Alfred A. Knopf
%C New York
%G ISBN 978-0-307-27270-6
%K medicine, science
%O source lists, index
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