Previously: Mainstream Nutrition Science on Obesity, Atkins Redux, Did the US Government Give Us Absurd Advice About Sugar?

In this post, I'm going to deal with an issue that's central to Gary Taubes' critique of mainstream nutrition science: what causes obesity?

This is a post a post I found exceptionally difficult to write. You see, while his 2002 New York Times article portrays mainstream nutrition science as promoting a simplistic mirror-image of the Atkins diet, his books do manage to talk about the mainstream view that if you consume more calories than you burn you'll gain weight... sort of. As I looked closely at the relevant chapters of those books, it became less and less clear what view he's attributing to mainstream experts, or what his alternative is supposed to be.

Because this discussion may get confusing, I want to start by repeating what I said in my first post: the mainstream view is that people gain weight when they consume more calories than they burn, but both calorie intake and calorie expenditure are regulated by complicated mechanisms we don't fully understand yet.

Yet Taubes goes on at great length about how obesity has other causes beyond simple calorie math as if this were somehow a refutation of mainstream nutrition science. So I'm going to provide a series of quotes from relevant sources to show that the experts are perfectly aware of that fact. All of the following sources are ones Taubes cites as examples of how absurd the views of mainstream nutrition experts supposedly are:

The etiology of obesity is multifactorial and includes genetic, neurohormonal, endocrine, metabolic and life-style-associated factors. Generally, obesity is a result of excess energy resulting from disturbances in the energy intake/expenditure equilibrium.

Report From FDA's Sugars Task Force. 1986. p. S14.

The causes of obesity are incompletely understood, so that effective treatment is difficult. Obesity is the net result of an excess of energy consumption over expenditure. Factors that must be considered as contributing to causation are: (1) heredity, (2) primary overeating, (3) altered metabolism of adipose tissue, (4) defective or decreased thermogenesis (the process by which calories are converted into heat), (5) decreased physical activity without an appropriate reduction in food intake, and (6) certain prescribed medications. These potential causes can interact with one another. Of the six factors, individuals may have some control of overeating and underactivity.

The Surgeon General's Report on Nutrition and Health. 1988. p. 290.

Positive energy balance can result from increased energy intake, reduced energy expenditure, or both, and over the long term, can lead to obesity and its associated complications... Obesity is enhanced not only by this energy imbalance but also by a genetic predisposition to obesity and altered metabolic efficiency... The specific causes of obesity are not well known, although some obese people clearly consume more energy compared to people of normal weight, whereas others are very sedentary or may have increased metabolic efficiency.

1989 National Academy of Sciences Diet and Health report. 1989. p. 10.

Maintenance of a normal body weight requires a match of food intake to energy expenditure... Both nutrient intake and energy expenditure are regulated by a complex interaction between the periphery and the central nervous system. Although not all aspects of central-peripheral interactions involved in energy balance are understood, key factors have been identified. For example, leptin from the adipocyte, ghrelin from the stomach, peptide YY from the gut, and insulin from the pancreas are all involved in the central regulation of energy balance. In the brain, more than a dozen peptides have been implicated in appetite and satiety.

Article on obesity on Joslin's Diabetes Mellitus. p. 536.

There's also the Handbook of Obesity (whose first edition sadly does not appear to be easily accessible online), which I attempt won't quote from because it devotes dozens of chapters to the etiology of obesity, including chapters titled "The Genetics of Human Obesity," "Behavioral Neuroscience of Obesity," and "Endocrine Determinates of Obesity."

Now what exactly is Taubes' objection to the above statements? It's easy to find answers to this question in his books. It's less easy to reconcile all the different answers with each other. At times, he seems to suggest the above statements are self-contradictory, such as when he gives the following example of an "apparent contradiction" (in Good Calories, Bad Calories on p. 271):

It may be true that, “for the vast majority of individuals, overweight and obesity result from excess calorie consumption and/or inadequate physical activity,” as the Surgeon General’s Office says, but it also seems that the accumulation of fat on humans and animals is determined to a large extent by factors that have little to do with how much we eat or exercise, that it has a biologic component.

At times like this, Taubes reminds me of the biologists who Ernst Mayr chided in his paper "Cause and Effect in Biology" for failing to realize that biological phenomenon can be cause on multiple levels. Mayr quotes an example:

The earlier writers explained the growth of the legs in the tadpole of the frog or toad as a case of adaptation to life on land. We know through Gundernatsch that the growth of the legs can be produced at any time even in the youngest tadpole, which is unable to live on land, by feeding the animal with the thyroid gland.

Just as there's no contradiction between thinking leg growth in tadpoles is controlled by hormones, and thinking this mechanism is an evolutionary adaptation, there's no contradiction between thinking weight gain is the result of consuming more calories than you burn, and also thinking that there are a lot of different factors that influence calorie intake and expenditure.

But maybe Taubes doesn't mean to suggest there's a contradiction there. He goes to great lengths to assure his readers he isn't rejecting the laws of thermodynamics. Furthermore, he doesn't seem interested in claiming any loopholes in the basic calories-in, calories-out math along the lines of Atkins' ketones-in-the-urine hypothesis. Instead, the idea often seems to be that the calories-in, calories-out idea is true but trivial. Why We Get Fat (p. 74) offers this analogy:

Imagine that, instead of talking about why we get fat, we're talking about why a room gets crowded...

If you asked me this question and I said, Well, because more people entered the room than left it, you'd probably think I was being a wise guy or an idiot. Of course more people entered than left, you'd say. That's obvious. But why?

This is a poor analogy, because the fact the importance of calories in weight gain is far less obvious than the importance of people in a room's getting crowded. Imagine: what if it had turned out that it's the total mass of your food that matters? Or just the total grams of fat? Or just the total grams of carbs? Or the phlogiston content?

A poorly-chosen analogy, though, is a minor problem compared to the false implication that mainstream that obesity researchers have ignored the factors that influence calorie intake and expenditure. This is a claim that Taubes makes explicit in other cases, for example:

Good Calories, Bad Calories (p. 295):

What may be the single most incomprehensible aspect of the last half-century of obesity research is the failure of those involved to grasp the fact that both hunger and sedentary behavior can be driven by a metabolic-hormonal disposition to grow fat, just as a lack of hunger and the impulse to engage in physical activity can be driven by a metabolic-hormonal disposition to burn calories rather than store them.

Why We Get Fat (pp. 80-81):

Of all the dangerous ideas that health officials could have embraced while trying to understand why we get fat, they would have been hard-pressed to find one ultimately more damaging that calories-in/calories-out... it's misleading and misconceived on so many levels that it's hard to imagine how it survived unscathed and virtually unchallenged for the last fifty years...

There has to be a reason, of course, why anyone would eat more calories than he or she expends, particularly since the penalty for doing so is to suffer the physical and emotional cruelties of obesity. There must be a defect involved somewhere; the question is where.

The logic of calories-in/calories-out allows only one acceptable answer to this question. The defect cannot lie in the body-perhaps, as the endocrinologist Edwin Astwood suggested half a century ago, in the "dozens of enzymes" and the "variety of hormones" that control how our bodies "turn what is eaten into fat"—because this would imply that something other than overeating was fundamentally responsible for making us fat. And that's not allowed. So the problem must lie in the brain. And, more precisely, in behavior, which makes it an issue of character.

To which I reply: no, those involved in obesity research did not fail to grasp the factors that drive hunger and sedentary behavior, and there was no unchallenged dogma the causes of obesity can't lie in our bodies. Read your own damn sources, Taubes.

I wish I could end this post there, but there's a complication: what about those statements I talked about in part 2, that it's "not a medical fact" that losing weight requires cutting down on excess calories, and that dietary fat has no effect on fat accumulation in the body? Well, there is an explanation for those statements. It's something Taubes goes on at great length about in Good Calories, Bad Calories, but is perhaps most succinctly expressed in Why We Get Fat (p. 99): "We don't get fat because we overeat; we overeat because we're getting fat."

The part of me that's still trying to figure out how to be charitable to Taubes urges that surely that sentence wasn't meant to be taken too literally. To use Taubes' own analogy of the room getting crowded: it's one thing to say "the room is getting crowded because more people are entering than leaving" is too obvious to mention. It's another thing to say that that claim is false, and on the contrary it's the room getting crowded that's causing people to enter. (There's a sense in which that could be true given the phenomenon of social proof, but then we're talking about a feedback loop, not one-way causation.)

So it's natural to assume Taubes is playing with meaning here a bit, using "getting fat" to refer not to the weight gain itself but a metabolic tendency to get fat, or something like that. Surely he still recognizes that how much we eat still has an effect on our weight, right? On the one hand it seems that he does: he talks about how calorie intake affects calorie expenditure, but he doesn't claim they march so closely in lockstep that it's literally impossible to lose weight by cutting calorie intake. His discussion of low-calorie diets plays up how unpleasant they are, but he does acknowledge people lose weight on them. 

On the other hand... Taubes seems really serious about this claim, portraying it as one of the fundamental mistakes of mainstream nutrition experts. From Good Calories, Bad Calories (p. 293):

The first law of thermodynamics dictates that weight gain—the increase in energy stored as fat and lean-tissue mass—wil be accompanied by or associated with positive energy balance, but it does not say that it is caused by a positive energy balance—by “a plethora of calories,” as Russel Cecil and Robert Loeb’s 1951 Textbook of Medicine put it. There is no arrow of causality in the equation. It is equally possible, without violating this fundamental truth, for a change in energy stores, the left side of the above equation, to be the driving force in cause and effect; some regulatory phenomenon could drive us to gain weight, which would in turn cause a positive energy balance—and thus overeating and/or sedentary behavior. Either way, the calories in wil equal the calories out, as they must, but what is cause in one case is effect in the other.

All those who have insisted (and still do) that overeating and/or sedentary behavior must be the cause of obesity have done so on the basis of this same fundamental error: they will observe correctly that positive caloric balance must be associated with weight gain, but then they will assume without justification that positive caloric balance is the cause of weight gain. This simple misconception has led to a century of misguided obesity research.

He even goes so far as to say (in Why We Get Fat, p. 76):

The experts who say that we get fat because we overeat or we get fat as a result of overeating—the vast majority—are making the kind of mistake that would (or at least should) earn a failing grade in a high-school science class.

So what's going on here? I think the answer lies Taubes' eagerness to portray mainstream nutrition experts as big meanies who blame fat people for being fat. I've already quoted him as saying that on the mainstream view, being overweight or obese must result from a defect of character. Just to drive the point home, in the same book he later says (p. 84):

Much of the last half-century of professional discourse on obesity can be perceived as attempts to circumvent what we could call the "head case" implications of calories-in/calories-out: how to blame obesity on eating too much without actually blaming the fat person for the human weaknesses of self-indulgence and/or ignorance.

So if you hear an advocate of the mainstream view claiming not to be a big meanie, don't believe them!

But this puts Taubes in a bind: now if he says how much we eat has an effect on our weight, he's a big meanie too. It doesn't work for him to say fat people can't help overeating because of something wrong with their metabolism, and this in turn causes them to gain weight, because he's committed himself to the principle that blaming behavior equals blaming a character defect. So instead, we get wild rhetoric about how stupid the experts are with no coherent view underneath it.

A more sensible approach would've been to emphasize that akrasia is an extremely common problem for humans, and that people who don't suffer from akrasia in regards to diet probably suffer from akrasia about something else. But that wouldn't have made for as an exciting of a book. Robin Hanson once commented that "few folks actually care much about the future except as a place to tell morality tales about who today is naughty vs. nice." I suspect this point generalizes. If you want to sell a book, flatter your audience and give them some villains to hate.

I have no plans of discussing Taubes claims about carbohydrates having a unique ability to mess up the systems that regulate weight. For one thing, I don't have anything to add to what others have already said. For another, one thing Taubes is definitely not claiming is, "while obesity researchers have spent a great deal of time studying the mechanisms that regulate weight, they've completely failed to realize how badly carbs screw up these mechanisms."

Instead, he accuses them of ignoring the relevant mechanisms entirely. This claim is so wildly untrue as to be grounds to doubt anything you think you learned from Taubes—indeed, to doubt any ideas you originally got from him even if you thought you later got confirmation for them elsewhere.

Closing thought: it's quite possible for a majority of the experts to be wrong. And I can even imagine finding a case somewhere where a non-expert rationally arrived at the correct answer when 95% of the experts are wrong—though I've been unable to actually find such a case. But when you see someone claiming that the vast majority of the experts have an obviously stupid view that should have earned them a failing grade in high school science, that is a very strong signal that you are dealing with a crackpot.