The Inanity of Overeating
Written on December 4, 2010 by GT in Obesity and weight regulation, bad science, calories-in-calories-out.My new book is coming out at the end of the month. It’s called Why We Get Fat and the subtitle is What To Do About it. The book concentrates more on the first because once you understand why we get fat, the what to do about it part is pretty obvious. And the problem is that the conventional wisdom on why we get fat is almost incomprehensibly naïve and wrong-headed.
My goals in writing the book, as I explain in an author’s letter, are to push the issue (I keep wanting to use the cliché, “throw down the gauntlet,” but as I get older I notice I keep wanting to use more and more clichés, and it’s a bad sign for a writer) on this nonsensical notion that we get fat because of overeating and sedentary behavior, and to distill down and extend some of the arguments from my previous book, Good Calories, Bad Calories, into a book that can easily be airplane reading on any flight covering more than one time zone.
In this blog, if it goes as planned, I hope to ask questions as much as provide answers. Over the past decade, as I’ve read more than a century’s worth of literature on obesity and nutrition and chronic disease, I’ve been consistently amazed at the ability of researchers, learned commentators (and the far greater ranks of unlearned commentators), physicians and public health authorities to accept some of the rote ideas about these excruciatingly important subjects without seemingly giving it any conscious thought whatsoever, or without wanting to ask the kinds of questions that a reasonably smart junior high school student should ask if given the opportunity. To this date, I don’t understand this failure of intellect, although I’ll almost assuredly be returning to it regularly in future blogs.
So what do I mean about overeating being a nonsensical explanations for why we get fat? I was just reading Jonah Lehrer’s latest column in the Wall Street Journal–“The Real Culprit in Overeating.”
Now Lehrer is one of the most talented science writers working today. I’m tempted to say one of the brightest young science writers, but that would be to do him a disservice. He’s as good as any of us at any age. But in this column he falls short, as he’s working outside his area of expertise. (A common problem with most science and health writers is that we often write about a different subject every week or month, so if we’re being fed nonsense by the local experts in any particular field we will typically pass that nonsense along to the readers because we don’t know enough not do otherwise.) The underlying assumption of Lehrer’s column is that we get obese because we overeat, and evidence of the fact that Americans eat too much is that a third of us are obese. Okay, so let’s take a look at this concept from a less than conventional perspective and see what questions we might naturally ask.
First, obese people tend to be weight stable for long periods of their life, just like lean people. So when they’re weight stable, the obese and overweight are obviously in energy balance. They’re not overeating during these periods of stable weight. They’re eating to match their expenditure, doing exactly what the lean do (and get copious credit for). So one obvious question is why the overweight and obese are only in energy balance when they’re carrying 10, 20, 30 or maybe 100 pounds of excess fat, and lean people are in energy balance without the excess? What’s the culprit for that? Because the problem isn’t that the obese overeat when they’re obese, it’s that they overeat when they’re lean and they continue to overeat until they become obese.
Second, let’s say you’re carrying around 40 pounds of excess fat and you put on that 40 pounds over the course of 20 years, as many of us do. When you’re in your late 20s, say, you’re still lean, and then, lo and behold, you celebrate your fiftieth birthday and you’re obese and your doctor is lecturing you on eating less and getting to the gym regularly (and probably writing you a prescription for Lipitor, as well). Now, if you gain 40 pounds of fat over 20 years, that’s an average of two pounds of excess fat accumulation every year. Since a pound of fat is roughly equal to 3500 calories, this means you accumulate roughly 7000 calories worth of fat every two years. Divide that 7000 by 365 and you get the number of calories of fat you stored each day and never burned – roughly 19 calories. Let’s round up to 20 calories, so we have a nice round number. (In the new book I discuss this issue in a chapter called “The Significance of Twenty Calories a Day.”)
So now the question: if all you have to do to become obese is store 20 extra calories each day on average in your fat tissue — 20 calories that you don’t mobilize and burn — what does overeating have to do with it? And why aren’t we all fat? Twenty calories, after all, is a bite or two of food, a swallow or two of soda or fruit juice or milk or beer. It is an absolutely trivial amount of overeating that the body then chooses, for reasons we’ll have to discuss at some point, not to expend, but to store as fat instead. Does anyone – even Jonah Lehrer or the neuroscientists he consults – think that the brain, perhaps in cohort with the gut, is making decisions about how much we should eat, on how long we stay hungry and when we get full, so that we don’t overshoot by 20 calories a day. That’s matching intake to expenditure with an accuracy of better than 1 percent. (We consume, on average, about 2700 calories a day, so matching energy in to energy out and not overshooting by 20 calories requires better than one percent accuracy.) And, of course, if we only overshoot by ten calories a day on average, we’re still going to put on 20 pounds of excess fat in 20 years. So really when we talk about being in energy balance – or practicing energy balance, as the experts now like to say – we actually have to be perfect in our matching of intake to expenditure or we’re going to get inexorably fatter (or leaner, if we err on the side of going hungry), or at least we have to average perfection over decades.
One way to get around this is to assume that we overeat by this trivial amount for a few years on end and then we realize we’ve put on five or ten pounds – maybe our clothes no longer fit well or we’ve had to let out the belt a notch or two – and then we decide to undereat every day for however long it takes to make up for it. So now we walk away from the table hungry until all is back to leanness. But then how do animals do it? They don’t have mirrors or clothes to tell them they’re getting fat, and the world is full of animals that have plenty of food available all year round, plenty of opportunity to overeat if they want to and do so long enough to get chubby. And yet the only animals that get chronically obese are those that get their food directly from humans – in the laboratory, in the home or the zoo, or at the dinner table, since humans happen to be animals, too.
Considering the fact that not getting fatter year in and year out means literally matching energy in to energy expended without error for years on end, do we really think that this job is done by the brain, by either conscious behavior, or some system that listens to signals from the body and then puts a halt on eating behavior when it decides enough food has come in that the amount so far expended or likely to be expended in the near future is about to be exceeded? Here’s the idea: your gut is sending signals to this monitoring system in the brain and that monitoring system is tallying up calories consumed until it finally senses that it’s near the limit of intake. Uh oh, it’s thinking, that last bite of that hamburger is not going to be expended, abort abort! Put down the fork! Walk away from the table!
If you were designing an organism that didn’t accumulate excess fat in the fat tissue (in other words, any organism that isn’t human or isn’t getting fed by humans, directly or indirectly) would you leave it up to a different organ entirely, an organ off-site so to speak (the brain), to assure that calories consumed matched calories expended, so that no excess energy managed to somehow sneak into the fat tissue, without the fat tissue having any say in the matter? Or would you give the regulation to the fat tissue itself and let it do the job?
The reason people believe we get fat because of overeating and sedentary behavior is because they believe the laws of thermodynamics somehow dictate this to be true. In particular the first law, which tells us that energy is conserved, so if a system takes in more energy than it expends, the energy contained in the system has to increase. If that system happens to be our fat tissue, than the fat tissue accumulates fat. That’s the logic. So if we eat more than we expend, we get fatter and the logic turns this around to say that we get fat because we eat more than we expend. And so, overeating and sedentary behavior are the causes. This is the logic that leads virtually every government health agency and independent health organization (the AHA, the AMA, you name it) to have some variation of this World Health Organization statement on its website or in its promotional material: “The fundamental cause of obesity and overweight is an energy imbalance between calories consumed on one hand, and calories expended on the other hand.”
But now imagine that instead of talking about why we get fat, we’re talking about a different system entirely. This kind of gedanken (thought) experiment is always a good way to examine the viability of your assumptions about any particular problem. Say instead of talking about why fat tissue accumulates too much energy, we want to know why a particular restaurant gets so crowded. Now the energy we’re talking about is contained in entire people rather than just the fat in their fat tissue. Ten people contain so much energy; eleven people contain more, etc.. So what we want to know is why this restaurant is crowded and so over-stuffed with energy (i.e., people) and maybe why some other restaurant down the block has remained relatively empty — lean.
If you asked me this question — why did this restaurant get crowded? — and I said, well, the restaurant got crowded (it got overstuffed with energy) because more people entered the restaurant than left it, you’d probably think I was being a wise guy or an idiot. (If I worked for the World Health Organization, I’d tell you that “the fundamental cause of the crowded restaurant is an energy imbalance between people entering on one hand, and people exiting on the other hand.”) Of course, more people entered than left, you’d say. That’s obvious. But why? And, in fact, saying that a restaurant gets crowded because more people are entering than leaving it is redundant –saying the same thing in two different ways – and so meaningless.
Now, borrowing the logic of the conventional wisdom of obesity, I want to clarify this point. So I say, listen, those restaurants that have more people enter them then leave them will become more crowded. There’s no getting around the laws of thermodynamics. You’d still say, yes, but so what? Or at least I hope you would, because I still haven’t given you any causal information. I’m just repeating the obvious.
This is what happens when the laws of physics (thermodynamics) are used to defend the belief that overeating makes us fat. Thermodynamics tells us that if we get fatter and heavier, more energy enters our body than leaves it. Overeating means we’re consuming more energy than we’re expending. It’s saying the same thing in a different way. (In 1954, the soon-to-be-famous — and often misguided, although not in this case — nutritionist Jean Mayer said that to explain obesity by overeating was about as meaningful as explaining alcoholism by overdrinking, and merely reaffirmed, quite unnecessarily, the fact that the person saying it believed in the laws of thermodynamics.) Neither happens to answer the question why. Why do we take in more energy than we expend? Why do we get fatter?
Answering the “why” question speaks to actual causes. In the restaurant analogy, okay, maybe this restaurant has particularly great food, or it’s happy hour; the drinks are cheap. Maybe it’s pouring outside so a lot of people ran into the restaurant to stay dry. Maybe every other restaurant in the neighborhood, including our lean restaurant down the block, was recently closed by the local health bureau and this is the only one that didn’t have cockroaches in the kitchen and so remained open. Maybe it’s in the theater district and the shows just got out and now every restaurant in the neighborhood is packed with the post-theater crowd. Maybe the word has spread that Brad Pitt and Angelina Jolie frequent this restaurant regularly, or Oprah, and this attracted a crowd hoping for a glimpse of celebrity.
All these would be valid answers to the question we asked. Some speak to the conditions inside the restaurant (the quality of the food, the price of the drinks, celebrity customers); some speak to conditions immediately outside (a rain storm, no competition, the theater schedule). They all provide the causal information we’re seeking. They answer the “why” question. That more people are entering than leaving doesn’t. It’s what logicians call “vacuously” true. It’s true, but meaningless. It tells us nothing. And the same is true of overeating as an explanation for why we get fat. If we got fat, we had to overeat. That’s always true; it’s obvious, and it tells us nothing about why we got fat, or why one person got fat and another didn’t.
Some obesity experts are intuitively aware of this problem, which is why they’ll say, as the National Institutes of Health does on its website, that “Obesity occurs when a person consumes more calories from food than he or she burns.” By using the word occurs, they’re not actually saying that overeating is the cause, only a necessary condition. (It’s like saying “a crowded restaurant occurs when more people enter than leave.”) They’re just saying that when one thing happened – obesity –the other thing also happened – consuming more calories from food than we expend. And now it’s up to us to say, okay, so what? Aren’t you going to tell us why obesity occurs? Rather than tell us what else happens when it does occur.
As for the great majority of experts who say (and apparently believe) that we get fat because we overeat or we get fat as a result of overeating, they’re the ones making the junior-high-school-science-class mistake: they’re taking a law of nature that says absolutely nothing about why we get fat and assuming it says all that needs to be said. This was a common error in the first half of the 20th century. It’s become ubiquitous since.
If the experts had ever been open to a little skeptical thinking from others or had they been appropriately skeptical themselves, this might never have happened. What’s been needed (and still is) was for someone (a reasonably smart 14-year-old would suffice) to ask the obvious questions and then insist on intelligent answers. Here’s how such a dialog might go:
The experts: Obesity is caused by over-eating, by consuming more calories than are expended. There’s no getting around the first law of thermodynamics.
Us: But all that law says is that if somebody gets fat, they have to consume more calories then they expend. So why do they do that?
The experts: Because they do.
Us: That’s not a good enough answer.
The experts: Well, maybe they can’t help themselves.
Us: Why can’t they help themselves?
The experts: Because they can’t.
Us: That’s not a good enough answer either.
The experts: Because the food industry makes them do it. There’s so much good food around and it’s so tasty, they can’t help but eat it.
Us: But obviously some of us can, because we don’t all get fat. Why is it only some people can’t help themselves?
The experts: Because they can’t.
Us: Try again.
The experts: Well, it’s complicated.
Us: What do you mean complicated? We thought it was easy. Just this eating-too-much, exercising-too-little, calories-in-calories-out, thermodynamics thing.
The experts: Okay, how about this? [Now quoting from an NIH report published in 2000.] “Obesity is a complex, multifactorial chronic disease that develops from an interaction of genotype and the environment. Our understanding of how and why obesity develops is incomplete, but involves the integration of social, behavioral, cultural, physiological, metabolic and genetic factors.”
Us: So what do all those have to do with eating too much and the laws of thermodynamics?
Experts: They contribute to making fat people overeat.
Us: How do they do that?
The experts: We don’t know. It’s complicated.
Us: Then maybe there’s another way to look at it. Maybe when we get fat it’s because those physiological, metabolic and genetic factors you mentioned are dysregulating our fat tissue, driving it to accumulate too much fat, and that’s why we eat so much and appear — to you anyway — to be kind of lazy. We’re compensating for the loss of calories into our fat.
The experts: Yeah, well, maybe. Your guess is as good as ours.