Why We Get Fat: And What to Do About It (11 page)

It’s hard to imagine, in this case, that eating too much and exercising too little had anything to do with the fat he acquired. And if we can’t blame his belly fat on calories-in/calories-out, maybe we shouldn’t blame ours, either.

There is no getting around the laws of thermodynamics. This certainly is a very old and immutable message. Ever since the early 1900s, when the German diabetes specialist Carl von Noorden first argued that we get fat because we take in more calories than we expend, experts and non-experts alike have insisted that the laws of thermodynamics somehow dictate this to be true.

Arguing to the contrary, that we might actually get fatter for reasons other than the twin sins of overeating and sedentary behavior, or that we might lose fat without consciously eating less and/or exercising more, has invariably been treated as quackery—“emotional and groundless,” as the Columbia University physician John Taggart insisted in the 1950s in his introduction to a symposium on obesity. “We have implicit faith in the validity of the first law of thermodynamics.” he added.

Such faith is not misplaced. But that does not mean that the laws of thermodynamics have anything more to say about getting
fat than any other law of physics. Newton’s laws of motion, Einstein’s relativity, the electrostatic laws, quantum mechanics—they all describe properties of the universe we no longer question. But they don’t tell us why we get fat. They say nothing about it, and this is true of the laws of thermodynamics as well.

It is astounding how much bad science—and so bad advice, and a growing obesity problem—has been the result of the experts’ failure to understand this one simple fact. The very notion that we get fat because we consume more calories than we expend would not exist without the misapplied belief that the laws of thermodynamics make it true. When the experts write that “obesity is a disorder of energy balance”—a declaration that can be found in one form or another in much of the technical writing on the subject—it is shorthand for saying that the laws of thermodynamics dictate this to be true. And yet they don’t.

Obesity is not a disorder of energy balance or calories-in/calories-out or overeating, and thermodynamics has nothing to do with it. If we can’t understand this, we’ll keep falling back into the conventional thinking about why we get fat, and that’s precisely the trap, the century-old quagmire, that we’re trying to avoid.

There are three laws of thermodynamics, but the one that the experts believe is determining why we get fat is the first one. This is also known as the law of energy conservation: all it says is that energy is neither created nor destroyed but can only change from one form to another. Blow up a stick of dynamite, for instance, and the potential energy contained in the chemical bonds of the nitroglycerin is transformed into heat and the kinetic energy of the explosion. Because all mass—our fat tissue, our muscles, our bones, our organs, a planet or star, Oprah Winfrey—is composed of energy, another way to say this is that we can’t make something out of nothing or nothing out of something.

Oprah, for instance, can’t become more massive—fatter and heavier—without taking in more energy than she expends,
because Oprah fatter and heavier contains more energy than Oprah leaner and lighter.
^*
She has to consume more energy than she expends to accommodate her increasing mass. And she can’t become leaner and lighter without expending more energy than she takes in. Energy is conserved. That’s what this first law of thermodynamics tells us.

This is so simple that the problem with how the experts interpret the law begins to become obvious. All the first law says is that if something gets more or less massive, then more energy or less energy has to enter it than leave it. It says nothing about why this happens. It says nothing about cause and effect. It doesn’t tell us why anything happens; it only tells us what has to happen if that thing does happen. A logician would say that it contains no causal information.

Health experts think that the first law is relevant to why we get fat because they say to themselves and then to us, as the
The New York Times
did, “Those who consume more calories than they expend in energy will gain weight.” This is true. It has to be. To get fatter and heavier, we
have
to overeat. We have to consume more calories than we expend. That’s a given. But thermodynamics tells us nothing about why this happens,
why
we consume more calories than we expend. It only says that if we do, we will get heavier, and if we get heavier, then we did.

Imagine that, instead of talking about why we get fat, we’re talking about why a room gets crowded. Now the energy we’re discussing is contained in entire people rather than just their fat tissue. Ten people contain so much energy, eleven people contain more, and so on. So what we want to know is why this room is crowded and so overstuffed with energy—that is, people.

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?
And, in fact, saying that a room 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 rooms that have more people enter them than 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 thermodynamics is used to conclude 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 says the same thing in a different way. Neither happens to answer the question why. Why do we take in more energy than we expend? Why do we overeat? Why do we get fatter?
^*

Answering the “why” question speaks to actual causes. The National Institutes of Health says on its website, “Obesity occurs when a person consumes more calories from food than he or she burns.” By using the word “occurs,” the NIH experts are not actually saying that overeating is the cause, only a necessary condition. They’re being technically correct, but 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?

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. They’re taking a law of nature that says absolutely nothing about why we get fat and a phenomenon that has to happen if we do get fat—overeating—and assuming these say all that needs to be said. This was a common error in the first half of the twentieth century. It’s become ubiquitous since. We need to look elsewhere for answers.

A good place to start might be a National Institutes of Health report published back in 1998. Back then, the NIH experts were a little more forthcoming, and so a little more scientific, about the factors that might cause obesity: “Obesity is a complex, multifactorial chronic disease that develops from an interaction of genotype and the environment,” they explained. “Our understanding of how and why obesity develops is incomplete, but involves the integration of social, behavioral, cultural, physiological, metabolic and genetic factors.”

So maybe the answers to be found are in this integration of factors—starting with the physiological, metabolic, and genetic ones and letting them lead us to the environmental triggers. Because the one thing we should know for sure is that the laws of thermodynamics, true as they always are, tell us nothing about why we get fat or why we take in more calories than we expend while it’s happening.

Before leaving thermodynamics behind, let’s clear up one more misguided extrapolation of these laws to the world of diet and weight. The very notion that expending more energy than we take in—eating less and exercising more—can cure us of our weight problem, make us permanently leaner and lighter, is based on yet another assumption about the laws of thermodynamics that happens to be incorrect.

The assumption is that the energy we consume and the energy we expend have little influence on each other, that we can consciously change one and it will have no consequence on the other, and vice versa. The thinking is that we can choose to eat less, or semi-starve ourselves (reduce calories-in), and this will have no effect on how much energy we subsequently expend (calories-out) or, for that matter, how hungry we become. We’ll feel just as full of pep if we eat twenty-five hundred calories a day as if we consume half that amount. And by the same token, if we increase our expenditure of energy, it will have no influence on how hungry we become (we won’t work up an appetite) or on how much energy we expend when we’re not exercising.

Intuitively we know this isn’t true, and the research in both animals and humans, going back a century, confirms it. People who semi-starve themselves, or who are semi-starved during wars, famines, or scientific experiments, are not only hungry all the
time (not to mention cranky and depressed) but lethargic, and they expend less energy. Their body temperatures drop; they tend to be cold all the time. And increasing physical activity
does
increase hunger; exercise does work up an appetite; lumberjacks do eat more than tailors. Physical activity also makes us tired; it wears us out. We expend less energy when the activity is over.

In short, the energy we consume and the energy we expend are dependent on each other. Mathematicians would say they are
dependent
variables, not
independent
variables, as they have typically been treated. Change one, and the other changes to compensate. To a great extent, if not entirely, the energy we expend from day to day and week to week will determine how much we consume, while the energy we consume and make available to our cells (a key point, as I will discuss later) will determine how much we expend. The two are that intimately linked. Anyone who argues differently is treating an extraordinarily complex living organism as though it were a simple mechanical device.

In 2007, Jeffrey Flier, dean of Harvard Medical School and his wife and colleague in obesity research, Terry Maratos-Flier, published an article in
Scientific American
called “What Fuels Fat.” In it, they described the intimate link between appetite and energy expenditure, making clear that they are not simply variables that an individual can consciously decide to change with the only effect being that his or her fat tissue will get smaller or larger to compensate.

What the Fliers accomplished in just two sentences is to explain why a hundred years of intuitively obvious dietary
advice—eat less—doesn’t work in animals. If we restrict the amount of food an animal can eat (we can’t just tell it to eat less, we have to give it no choice), not only does it get hungry, but it actually expends less energy. Its metabolic rate slows down. Its cells burn less energy (because they have less energy to burn). And when it gets a chance to eat as much as it wants, it gains the weight right back.

The same is true for humans. I don’t know why the Fliers said “an animal” instead of “a person,” since the same effects seen in animal studies have been demonstrated repeatedly in humans. One likely answer is that the Fliers (or the magazine’s editors) didn’t want the implication to be quite so obvious: that the diet advice that our doctors and public-health authorities are invariably giving us is misconceived; that eating less and/or exercising more is not a viable treatment for obesity or overweight and shouldn’t be considered as such. It might have short-term effects but nothing that lasts more than a few months or a year. Eventually, our bodies compensate.