This post considers why, given all the evidence against it, the calorie-in-calorie-out theory of weight has such a grip on people's imaginations.
I started thinking about this because a couple of weeks ago I was looking up some boring nutrition thing online and I came across the website of Dr. Jason Fung, a doctor and kidney specialist. Dr. Fung has a theory about obesity being cause not by overeating but rather by excessive insulin. I found it interesting enough to buy and read his book, The Obesity Code.
The Obesity Code draws on a range of evidence to argue against the calories-in-calories-out model -- in which weight gain and loss is governed by amounts of food and exercise -- and in favor of a different model, in which there are many factors but hormones -- and especially insulin -- are central. Insulin acts to direct the body's regulatory system: too much insulin and we gain weight. It's like a thermostat set at the wrong temperature.
I gather this is similar to what other people, like Gary Taubes, have been saying. But Dr. Fung adds an interesting point about meal timing. The main problem, Dr Fung says, is that our modern way of eating -- lots of carbohydrates, lots of "small meals" and snacking -- generates a lot of insulin. Frequent eating means that insulin is released often, and this means that our bodies develop a resistance to it -- just as they develop resistance to other things like drugs. We need more and more to get the effect insulin is supposed to provide, of helping us process sugar, and the body produces more and more insulin. And we gain weight.
The solution is to eat fewer carbohydrates, especially processed ones, but also to pay attention to meal timing. Don't snack. And if you want to lose weight, try skipping meals or fasting.
I'm not a physiologist so obviously I can't assess the scientific evidence of this book, but you don't have to be a scientist to know there is something very wrong with the idea of "calories-in-calories-out." You can easily observe that if you give the same food to different people their bodies will respond differently. In fact, if you give the same food to the same people at different times of their lives their bodies will respond differently.
Right at the start of his book Dr. Fung mentions several obvious examples of the how the calories-in-calories-out model obviously fails. Prior to puberty, boys and girls have the same body fat percentage. After puberty, women have almost 50 percent more body fat, despite eating less. Pregnancy induces weight gain, beyond the effect of eating more. Various drugs are known to cause weight gain, regardless of food intake. If you give people insulin, they gain weight; in fact there's a thing called "diabulemia" where people with Type 1 diabetes deliberately give themselves less insulin than they need, in order to lose weight.
Given all of this easily observable evidence, isn't it strange how often people, including scientists and health care professionals, constantly bring up this idea of calories-in-calories-out? The idea that to lose weight you should eat less and move more is like gospel in this country.
Proponents of calories-in-calories out would, I expect, want to say something like this: Sure, we know that there are many factors influencing the body. The idea of calories-in-calories-out doesn't mean calories are the only factor. It just means that "all things being equal," the more calories you take in and the fewer you use, the more you'll gain weight. Sometimes this is followed up with "It's thermodynamics! You can't change the laws of thermodynamics!"
I find this response unpersuasive. Obviously, I think it's true at some level that biochemical processes obey the laws of science. But so what? If there are many factors contributing to weight, then what is the point of saying calories-in-calories out? Even if it is true, it is irrelevant.
It's especially irrelevant if you're looking for understanding and explanation of cause and effect. Adapting one of Dr. Fung's analogies, imagine if you were looking to explain why a plane crash happened, and the answer was "there was not enough lift to overcome gravity." Yes, this is a law of physics. But how is it relevant? What we want to know is whether there was human error or mechanical problems or weather or what.
To say calories-in-calories-out and imply that it is relevant is to say something else: that if a person choses to eat less and move more, they will lose weight, and vice versa. This is the statement we're arguing about. It is clearly debatable, and there is increasing evidence that it is false. There's a large genetic component to weight. Foods like olive oil are processed differently from foods like sugar. Fat stores are regulated through homeostasis. The body is not a machine, but rather a delicately responsive organism that regulates itself through all kinds of delicately tuned mechanisms.
And yet, you can't get away from calories-in-calories-out. It's brought up all the time, sometimes in a sneering tone. It's the cornerstone of policies like the Obama administration's "Let's Move" campaign. Just the other day I read something on the Guardian presenting a multifactorial theory, and bam -- first comment I saw was about how, duh, you can't break the laws of thermodynamics. Why does everyone love to say and believe this? Here are a few thoughts.
1. The simplicity fetish
Modern westerners love a simple theory. I don't know what it is that makes people think a simpler theory is better than a more complicated one, especially when you're dealing with complex things like nutrition. In my book, Moral Reasoning in a Pluralistic World, I talk about how, even in ethics, people show a preference for simple theories organized around a single principle, despite the fact that most of us value various things -- such as justice, liberty, and overall well-being -- that are different and can obviously conflict.
I don't know if people just got over excited about the simplicity of modern physics, expressed in those elegant equations, or what, but this is definitely a thing. Somehow the idea that you could express the complexities of nutrition through a single equation -- I think it appeals to people on some visceral level.
2. The harmony myth
I think there's also a vague and often subconscious preference for seeing things all fit together, as if things that are good in one way are good in other ways and vice versa. High calorie foods strike some people as indulgent, and some high calorie foods, like meat, are a problem from an ethical and environmental point of view. As with the "harmony myth of human nature," we think it should all fit together. But of course it doesn't.
There's really no reason certain foods can't be bad from one point of view and good from another.
3. Politics and capitalism
One of the most interesting ideas in The Obesity Code is the idea that capitalism creates pressure for governments to endorse a calorie theory of weight. Because here's what the calories-in-calories-out theory doesn't say: it doesn't say "don't eat that." If official policy said to avoid starchy foods, the grain industry would have a freak out. By falsely treating all foods as the same, the calories-in-calories-out theory avoids demonizing any particular food, and thus satisfies certain political pressures.
In general, the capitalism angle on nutrition is pretty out of control. Nina Teicholz's book The Big Fat Surprise is full of hair-raising stories about how much of modern food science is funded by giant food corporations and industry. I think of myself as skeptical and cynical, but even I was shocked at the role olive oil companies played in organizing lush mega-conferences around the concept of the "Mediterranean diet."
Since this post is about weight gain and weight loss, I'd like to end by reminding everyone that weight is not a predictor of health, and that people can be healthy at any size. In fact, I expect the same dysfunctions creating chaos in the world of nutrition are also getting creating some of the misplaced hysteria over weight.
Someday, a social epistemologist is going to have a field day with the whole thing.