Everyone knows that eating fatty foods is bad for you, that high cholesterol causes heart disease and that we should all do some more exercise so that we can lose weight. How do I know that everyone knows this? Well, for one thing, this government website tells me so:
We all know too much fat is bad for us. But we don't always know where it's lurking. It seems to be in so many of the things we like, so it's sometimes difficult to know how to cut down.
...kids need to do at least 60 minutes of physical activity that gets their heart beating faster than usual. And they need to do it every day to burn off calories and prevent them storing up excess fat in the body which can lead to cancer, type 2 diabetes and heart disease.
See, it's right there in black and white. We all know too much fat is bad for us. Except... there are a lot of people who don't agree. Gary Taubes is one of them, His book, Good Calories Bad Calories (The Diet Delusion in the UK and Australia), sets out the case against what he calls the Dietary Fat Hypothesis for obesity and heart disease, and proposes instead the Carbohydrate Hypothesis: that both obesity and heart disease are caused by excessive consumption of refined carbohydrates, rather than dietary fat.
Taubes is very convincing. He explains how people have consistently recommended low-carb diets for weight-loss for the past 150 years. He explains how scientists roundly ignored studies that contradicted the link between high cholesterol and coronary disease. There are details of the mechanism by which eating refined carbohydrate affects insulin production, leading to obesity. He gives a plausible narrative for how the Dietary Fat Hypothesis came to be accepted scientific wisdom despite not actually being true (or supported by the majority of the evidence). He explains how studies of low-fat diets simply ignored overall mortality rates, reporting only deaths from heart disease, and how one study wasn't published because 'we weren't happy with the way it turned out'. All in all, the book is very convincing.
I expect a relatively large percentage of people on LW are already aware of this. Searching the LW archives for 'Taubes' gives several, mostly positive, references to his work (Eliezer seems to be convinced "Dietary scientists ignoring their own experimental evidence have killed millions and condemned hundreds of millions more to obesity with high-fructose corn syrup."). However, I do expect it to be news to some people, and I think it raises an important question. Given that everyone needs to eat something, we all need to decide whether we believe Taubes or whether we believe Change 4 Life.
Good Calories, Bad Calories is 601 pages of relatively small type, and contains 111 pages of references. Most of you probably don't want to read a book that long, and you definitely don't want to check all of it's references. Even if you did, Taubes openly admits that his book is attempting to argue for the Carbohydrate Hypothesis - he is trying to convince you, why should you be surprised if you find yourself convinced? (He claims not to be cherry-picking but then, he would, wouldn't he?) So how can you decide whether to trust the government or whether to trust some journalist with no training in biology? Even if you do decide to assess the evidence for yourself, how exactly should you go about it?
This is the key question of rationality. How can we believe what is true? And I think this makes a great case study - it's an area in which we all have to have a belief (or at least, act as though we have a belief) and one in which there is (or at least appears to be) genuine controversy as to what is true and what is not.
If you've already thought about this, do you believe Taubes' thesis, and how did you come to this conclusion? If this is the first time you've ever heard of Taubes, how far have you shifted your probability for the Dietary Fat Hypothesis based on reading this post? What more research do you intend to do to decide whether or not to continue believing it? How much weight do you place on the fact that I believe Taubes? On the fact that Eliezer believes Taubes (Eliezer, if your position is more nuanced than this, feel free to correct me)? How much did you update your beliefs based on what other commentors have said (assuming there have been any)?
One problem with all these debates about nutrition and exercise is that they mostly don't take into account individual differences. How exactly your body will react to a certain regime of diet and exercise, and which regimes are compatible with reaching and maintaining your optimal weight while feeling good and healthy -- the correct answers to these questions depend very strongly on your genotype, and possibly also on a number of entirely non-obvious and unknown environmental and lifestyle factors. (And to make things especially un-PC, the relevant genetic factors seem to correlate strongly with ethnic origin, since they've evolved significantly during the last few thousand years. This has been proven conclusively only for a few things like lactose tolerance, but it seems quite plausible that analogous group differences exist for other nutrients too.)
Therefore, except for a few simple observations like e.g. that you need some vitamin C to avoid scurvy, promoting certain diet guidelines as universally valid for all humans can't be other than nonsense. It's similar to those silly government propaganda campaigns about "safe" drinking limits that supposedly hold for everyone, whereas in reality, some people can drink a bottle of whiskey a day and nevertheless live long and productive lives (and never even appear visibly drunk), while others would be killed sooner or later by a fraction of that -- and yet others suffer from complete alcohol intolerance and get sick even from a single drink. Similarly, I have no doubt that some people exist for whom carbohydrates are as bad as Taubes says, but I also have no doubt that for many others, his claims are exaggerated to the point of nonsense, and I strongly suspect that the latter group includes a great majority of individuals in at least some ethnic groups.
As the bottom line, until scientists gain a much better understanding of the genetic and other factors involved, there really is no good way to go except self-experimentation. The only time I got into such a bad shape that I had to lose weight, I managed to devise a regime that enabled me to lose a pound a week with only a small expense of willpower, which was however completely unlike anything I've ever read from any side in the diet/exercise controversies -- and I doubt it would work for very many other people.
Exactly. The "Typical body fallacy".
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