Why We Get Fat

A book review

Posted by Peter Cresswell on May 10, 2017

The answer to the question “Why we get fat?” can be answered in the superficial and wrong way - “Because you eat too much” - or it can be answered in the literal, medical sense - “Because your fat cells are getting fat”. Whereas the first approach has jumped to the conclusion, the latter begs for follow up inquiry. Following that line of investigation leads to some really important discussions.

The book Why We Get Fat walks through the question of “Why We Get Fat” with a clear head of assumptions and, in asking the obvious but rarely asked questions, it challenges all popular assumptions and conclusions.

Why We Get Fat

You get fat because you eat too much

This is the classic answer that’s absolutely dead wrong. What’s worse, it’s extremely well entrenched in popular wisdom. This makes it the most obvious place to start busting myths.

In the early 1990s, the National Institutes of Health set out to investigate a few critical issues of women’s health. The result was the Women’s Health Initiative (WHI), a collection of studies that would cost in the neighborhood of a billion dollars. Among the questions that the researchers hoped to answer was whether low-fat diets actually prevent heart disease or cancer, at least in women. So they enrolled nearly fifty thousand women in a trial, chose twenty thousand at random, and instructed them to eat a low-fat diet, rich in fruits, vegetables, and fiber. These women were given regular counseling to motivate them to stay on the diet.

One of the effects of this counseling, or maybe of the diet itself, is that the women also decided, consciously or unconsciously, to eat less. According to the WHI researchers, the women, on average, consumed 360 calories a day less on their diets than they did when they first agreed to participate. If we believe that obesity is caused by overeating, we might say that these women were “undereating” by 360 calories a day. They were eating almost 20 percent fewer calories than what public-health agencies tell us such women should be eating.

The result? After eight years of such undereating, these women lost an average of two pounds each. And their average waist circumference—a measure of abdominal fat—increased. This suggests that whatever weight these women lost, if they did, was not fat but lean tissue—muscle.* How is such a thing possible? If our weight is really determined by the difference between the calories we consume and the calories we expend, these women should have slimmed down significantly. A pound of fat contains roughly thirty-five hundred calories’ worth of energy. If these women were really undereating by 360 calories every day, they should have lost more than two pounds of fat (seven thousand calories’ worth) in the first three weeks, and more than thirty-six pounds in the first year. And these women had plenty of fat to lose. Almost half began the study obese; the great majority were at the very least overweight.”

Why We Get Fat

You get fat because you don’t exercise enough

This is the sister lie to the above. It’s also very well established in the collective conscious. It’s also devastatingly wrong again.

One remarkable study of the effect of physical activity on weight loss was published in 1989 by a team of Danish researchers. The Danes actually did train sedentary subjects to run marathons (26.2 miles). After eighteen months of training, and after actually running a marathon, the eighteen men in the study had lost an average of five pounds of body fat. As for the nine women subjects, the Danes reported, “no change in body composition was observed.”

Why We Get Fat

You get fat because you eat too much fat

Another great lie that’s starting to lose traction.

After six years on the diet, these women had cut both their total fat consumption and their saturated-fat consumption by a quarter, lowering their total cholesterol and their LDL cholesterol below (albeit only very slightly below) that of the other twenty-nine thousand women, who were eating whatever they wanted and yet their low-fat diet, as the final reports stated, had no beneficial effect on heart disease, stroke, breast cancer, colon cancer, or, for that matter, fat accumulation. Eating less total fat and saturated fat, and replacing the fatty foods with fruits and vegetables and whole grains, had no observable beneficial effect at all.

Why We Get Fat

Or put another way:

It may be easier to believe that we remain lean because we’re virtuous and we get fat because we’re not, but the evidence simply says otherwise. Virtue has little more to do with our weight than with our height. When we grow taller, it’s hormones and enzymes that are promoting our growth, and we consume more calories than we expend as a result. Growth is the cause—increased appetite and decreased energy expenditure (gluttony and sloth) are the effects. When we grow fatter, the same is true as well.

We don’t get fat because we overeat; we overeat because we’re getting fat.

Why We Get Fat

It’s all about the Insulin

So if calories don’t matter and fat doesn’t matter, what does matter?

In a word: insulin.

In the presence of insulin, your body will convert glucose into fat. Think of this as the iron law of fat.

Here’s an illustrative example.

Excellent examples of how carefully animals (and so presumably humans, too) regulate their fat accumulation are hibernating rodents—ground squirrels, for example, which double their weight and body fat in just a few weeks of late summer. Dissecting these squirrels at their peak weight, as one researcher described it to me, is like “opening a can of Crisco oil—enormous gobs of fat, all over the place.

But these squirrels will accumulate this fat regardless of how much they eat, just like Wade’s ovary-less rats. They can be housed in a laboratory and kept to a strict diet from springtime, when they awake from hibernation, through late summer, and they’ll get just as fat as squirrels allowed to eat to their hearts’ content. They’ll burn the fat through the winter and lose it at the same rate, whether they remain awake in a warm laboratory with food available or go into full hibernation, eating not a bite, and surviving solely off their fat supplies.

The fact is, there’s very little that researchers can do to keep these animals from gaining and losing fat on schedule. Manipulating the food available, short of virtually starving them to death, is not effective.

Why We Get Fat

Wait. You’re telling me that fat accumulation is regulated not by the food available to an animal? That doesn’t make any sense. Well, actually it does make sense when you understand that the amount of food you eat does not control if you get fat or not and further understand that your hormones - in particular, insulin - control your fat.

In other words, the science itself makes clear that hormones, enzymes, and growth factors regulate our fat tissue, just as they do everything else in the human body, and that we do not get fat because we overeat; we get fat because the carbohydrates in our diet make us fat. The science tells us that obesity is ultimately the result of a hormonal imbalance, not a caloric one—specifically, the stimulation of insulin secretion caused by eating easily digestible, carbohydrate-rich foods: refined carbohydrates, including flour and cereal grains, starchy vegetables such as potatoes, and sugars, like sucrose (table sugar) and high-fructose corn syrup. These carbohydrates literally make us fat, and by driving us to accumulate fat, they make us hungrier and they make us sedentary.

Why We Get Fat

The book goes through a lot more of the research and is well worth a read, but if you’re looking for the short TL;DR version, then this is it. Keep your insulin levels down to prevent fat from accumulating. And keeping your insulin levels down is largely a question of avoiding eating sugars and carbohydrates.

It’s not about how much you eat. Nor is it about how much you exercise. It’s about what you eat.