The Science of Obesity

Why We Get Fat

One thing that has always baffled me is how we get fat.

Why We Get Fat by Gary Taubes unearths the biological truth around why we’re getting fat. In the process Taubes dispels many accepted ideas on weight-loss and nutrition.

While it’s easy to believe that we remain lean because we’re virtuous and we get fat because we lack self-control or discipline, the evidence clearly says otherwise. Taubes methodically tackles conventional (and governmental) wisdom and why it is wrong.

This is a biology book, not a diet book. It’s about the science of what’s happening in our body that makes us fat. Let’s explore Taubes argument.

Is this a simple calories-in calories-out problem?

Do low calorie diets work? In the short-term yes but overall, no.

“The two researchers who may have had the best track record in the world treating obesity in an academic setting are George Blackburn and Bruce Bistrian of Harvard Medical School. In the 1970s, they began treating obese patients with a six-hundred-calorie-a-day diet of only lean meat, fish, and fowl. They treated thousands of patients, said Bistrian. Half of them lost more than forty pounds.”

They concluded, “This is an extraordinarily effective and safe way to get large amounts of weight loss.” Yet, shortly after, Taubes says “Bistrian and Blackburn gave up on the therapy, because they didn’t know what to tell their patients to do after the weight was lost. The patients couldn’t be expected to live on six hundred calories a day forever, and if they returned to eating normally, they’d gain all the weight back.”

So, even if you lose weight on a low-calorie diet, you’re stuck with the what now problem.

What if i just exercise more?

What happens when we increase our energy expenditure by upping our physical activity? Taubes says “Considering the ubiquity of the message, the hold it has on our lives, and the elegant simplicity of the notion-burn calories, lose weight, prevent disease-wouldn’t it be nice if it were true?”

Alas, believing doesn’t make it so. While there are many reasons to exercise regularly, losing weight isn’t one of them.

Taubes looks at the evidence and walks us through a chain of reasoning. The evidence says obesity associates with poverty. In most modern parts of the world, the poorer people are, they fatter they are likely to be. Yet, it’s the poor and disadvantaged who sweat out a living with physical labour. This is one of the reasons to doubt the assertion that expending a large amount of energy on a regular basis makes us fat.

Another reason to doubt the calorie-out hypothesis is the obesity epidemic itself. We’ve been getting fatter for the past few decades which suggests that we’re getting more sedentary. Until the 1970′s, that is, before the obesity problem, Americans were not believers in the need to spend leisure time sweating.

In addition, it turns out there is very little hard evidence to support the belief that the number of calories we burn has any meaningful impact on how fat we become. The American Heart Association even calls the data supporting this claim “not particularly compelling.”

A study by Paul Williams and Peter Wood collected detailed information on almost 13k runners and then compared the weekly mileage with how much they weighed year-to-year. As you would expect, those who ran the most tended to weigh the least, but, perhaps unexpectedly, all these runners tended to get fatter with each passing year (even those running more than 40miles a week!)

According to Taubes, the belief in exercising more to weigh less is “based ultimately on one observation and one assumption. The observation is that people who are lean tend to be more physically active than those of us who aren’t. This is undisputed. … But this observation tells us nothing about whether runners would be fatter if they didn’t run or if the pursuit of distance running as full-time hobby will turn a fat man or woman into a lean marathoner. We base our belief in the fat-burning properties of exercise on the assumption that we can increase our energy expenditure (calories-out) without being compelled to increase our energy intake (calories-in).”

This assumption is wrong. We ended up buying into this exercise-more eat less story because it feels intuitive, correct, and reinforces our beliefs. We didn’t ask for evidence and none has been forthcoming in the intervening years.

Is it a matter of balancing calories?

No. Weight gain is a gradual process. So once you notice your jeans are getting tight, you can make some smart decisions and cut calories and increase physical activity right? “If it were true that our adiposity is determined by calories-in/calories-out, then this is one implication: you only need to overeat, on average, by twenty calories a day to gain fifty extra pounds in 20 years.” Now think of all the food decisions you make in a day and how impossible it would be, without scientific instrumentation, to balance your food.

Thermodynamics

Wait, what about thermodynamics. The law that says energy can be transformed from one form to another but not created nor destroyed. 

“The very notion that we get fat because we consume more calories that we expend would not exist without the misapplied belief that the laws of thermodynamics make it true. When 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.

All the first law of thermodynamics 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.”

Experts think the first law is relevant because it fits neatly with our existing theories about why we get fact—those who consume more calories than they burn will gain weight. Thermodynamics tells us that if we get fatter and heavier, more energy enters our body than leaves it. But the important question, at least from an obesity perspective, is why do we consume more calories than we expend?

One of the other problems with thermodynamics argument is the assumption that the energy we consume and the energy we exert have little influence on each other—that we can change one without impacting the other.

Literature says that animals whose food is suddenly restricted tend to reduce energy expenditure both by being less active and by slowing energy use in cells, thereby limiting weight loss. They also experience hunger so that once the restriction ends, they will eat more than their prior norm until the earlier weight is obtained. (This is the same problem Bistrian and Blackburn encountered earlier).

Another problem with Thermodynamics is that it doesn’t address why men and women fatten differently. This means, at least at some level, bodily functions and possibly genetics play a role.

When we believe, as we do, that people get fat because they overeat, we’re putting the ultimate blame on a weakness of character and leaving biology out of it. This implies that we can generally tell, just by looking at the waistline, which people have strong self-control.

Adiposity

In the early 1970′s George Wade studied the relationship between sex hormones, weight, and appetite by removing the ovaries from rats. The impact was dramatic: the previously skinny rats ate voraciously and became obese. “The rat eats too much, the excess calories find their way to the fat tissue, and the animal becomes obese,” offers Taubes. He continues, “this would confirm our preconception that overeating is responsible for obesity in humans as well. But Wade did a revealing second experiment, removing the ovaries from the rats and putting them on a strict postsurgical diet. Even if these rats were ravenously hungry after the surgery, even if they desperately wanted to be gluttons, they couldn’t satisfy their urge.” The rats still got just as fat, just as quickly. And that is the start of our understanding of why we actually get fat.

The animal doesn’t get fat because it overeats, it overeats because its getting fat. The animal is unable to regulate its fat tissue.

In a follow on experiment, where the rats were injected with estrogen after the surgery, resulted in normal behavior. That is, they did not become slothful or obese. Biologically, one of the things that estrogen does is to influence an enzyme called lipoprotein lipase (LPL). When cells want fat they express their interest by “expressing” LPL. If the LPL comes from a fat cell, we get fatter. If the LPL comes from a muscle cell, it gets pulled in and digested as fuel. LPL, according to Williams Textbook of Endocrinology, “is a key factor in partitioning triglycerides (i.e., fat) among different body tissues.”

One of Estrogen’s roles is to inhibit the activity of LPL “expressed” by fat cells. The rats in Wade’s experiments over-ate because they were losing calories into fat cells that were needed in other places. The fatter the rat got, the more it had to eat to feed the non-fat cells. When the body is unregulated, it creates a cycle of getting fatter and fatter.

This, as Taubes says, “reverses our perception of the cause and effect of obesity. It tells us that two behaviors—gluttony and sloth—that seem to be the reasons we get fat can in fact be the effects of getting fat.” It also tells us that influencing LPL (either positively or negatively) has a dramatic effect on how fat we get.

LPL also explains why men and women get fat in different spots and why exercise doesn’t work. In men, LPL, activity is higher in the gut and lower below the waist. In women, LPL is highest below the waist. Bad news though, after menopause, LPL in a woman’s abdomen catches up to the men. As for exercise, while we’re working out LPL activity decreases on our fat cells and increases on muscle cells—so far, so good—because this prompts the release of fat from out fat tissue so that muscles can use this as energy. When we stop exercising, however, the situation reverses. LPL activity on the muscle cells shuts down and LPL activity on fat cells picks up. The fat cells natural tendency is to get back to their previous state.

So what regulates all of this?

Insulin. The LPL on fat cells is regulated by the presence of insulin. The more insulin our body secrets, the more active the LPL becomes on the fat cells, and the more fat that, rather than being consumed as fuel by the muscle cells, gets stored in fat cells. As if designed to ensure we get fatter, insulin also reduces the LPL expressed by the muscle cells (to ensure there is lots of fat floating around for the fat cells). That is, it tells the muscle cells not to burn fat as a fuel.

Insulin also influences an enzyme called hormone-sensitive lipase, or HSL. And this, says Taubes, “may be even mroe critical to how insulin regulates the amount of fat we store. Just as LPL works to make fat cells (and us) fatter, HSL works to make at cells (and us) leaner. It does so by working inside the fat cells to break down triglycerides into their component fatty acids, so that those fatty acids can then escape into the circulation. The more active this HSL, the more fat we liberate and can burn from fuel and the less, obviously, we store. Insulin also surpresses this enzyme HSL and so it prevents triglycerides from being broken down inside the fat cells to a minimum.” This also helps explain why diabetics often get fatter when they take insulin therapy.

Carbohydrates primarily determine the insulin level in the blood. Here quantity and quality are important. Carbs ultimately determine how fat we get. But most people eat carbs so why are some fatter than others? We all naturally secrete a different level of insulin — given the same food people will secrete different levels of insulin. Another factor is how sensitive your cells are to insulin and how quickly they become insensitive. The more insulin you secrete—naturally or with carbohydrate rich foods—the more likely it is that your body becomes insulin resistant. The result is a vicious circle.

Not all foods containing carbs are equally fattening. The most fattening foods are those that have the greatest impact on our insulin and blood sugar levels. These are the easily digestible carbs. Anything made of refined flour (bread, cereals, and pasta), starches (potatoes, rice, and corn), and liquids (beer, pop, fruit juice). “These foods,” says Taubes, “flood the bloodstream quickly with glucose. Blood sugar shoots up; insulin shoots up; We get fatter.”

Here is an Taubes in a 70m video explaining more.

If you want to learn more about the science behind why we get fat, I recommend brushing up on your biology a little and reading Why We Get Fat. Taubes also wrote Good Calories Bad Calories.

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