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)?
I am an obesity researcher and I think that in some sense the idea that we are programmed to eat and to store fat for lean days is correct, and that our current environment of abundance combines with this innate tendency to increase the prevalence of obesity. But this general statement hides many unknowns. For example, why are some people more prone to weight gain than others (in the same environment)? Why is obesity heritable (20-80% heritable depending on how you calculate it and the population you use)? Taubes is absolutely correct in stating that the "low-fat diet" mantra was promoted without any evidence to back it up and the evidence we do have seems to favor low-carb diets, at least in the short run. Fructose (and its not just high fructose corn syrup...sucrose is 50% fructose, HFCS is 55% fructose) does indeed seem to be deleterious above and beyond just adding calories, but its not the whole story either. Toxins and endocrine disruptors may play a role, but we really dont know too much about that yet. Bottom line: the notion that we know NOTHING about nutrition is false. But the notion that we know all we need to know about diets and obesity is also false. The notion that higher carb intake is responsible for most of our increased weight gain is plausible (supported by data about total carb intake in the population..its the only macronutrient that has actually increased in per capita consumption. Fat intake has declined in the last 30 years, yet weight gain has accelerated) but not the whole story either. Its also worth keeping in mind that there is no one-to-one correlation between obesity and particular disease outcomes (diabetes, heart disease). On a public health level, there is an increased risk, but there are a very large number of "healthy obese" people; there is good evidence that modestly obese adults trying to lose weight have higher mortality than those whose weight remains static or slightly increases; there is very good evidence that most diets and other prescriptions dont work and lead to yo-yo weight change that may itself be unhealthier than the baseline moderate obesity; there is good evidence that lack of fitness is a far more significant risk factor for morbidity and mortality than BMI (in adults), and so on....the "moral panic" about obesity is not always grounded in sound science. "Prevention of obesity" by focusing on weight gain in children may bypass some of these concerns, but we have to be careful to see if we are responding to a fashionable moral panic or focusing on truly evidence-based fears AND interventions (even if the fears are real, all responses are not automatically justified; some responses to the disease may be worse than the original disease, others may be ineffective and hence a waste of time and money)?
I've heard this claim often, and I appreciate your pointing out that sucrose is hardly better than HCFS.
What evidence is there for human health being improved by avoiding fructose (on the margin, not absolutely)? Isn't it pretty weak? There are plenty of high-dose rat studies, but I don't typically adjust my lifestyle every time a rat study shows something.