Why Diets Make Us Fat summary

If a woman of average height who weighs 110 pounds lost 30 pounds, most people would agree she was too skinny and possibly malnourished. Yet if a woman who weighs 230 pounds lost 30 pounds, many people would congratulate her for shedding the excess weight.

To society, there’s a big difference in experience between these two women on a diet. Yet to the human brain, these scenarios are interpreted as dangerous: in both cases, the body thinks it’s starving.

Your body has evolved to keep your weight within a defended range; that is, your average weight plus or minus 10 or 15 pounds.

It’s relatively easy to achieve weight changes within your defended range through modifications in diet and exercise. The range itself can also shift, but it’s important to keep in mind that it’s far easier to raise the range than it is to lower it.

So while you can lose weight, once you drop below your defended range, your body will work hard to get you back to that level.

Why is this the case? Your brain maintains a highly effective energy-balance system, which automatically keeps your weight in its defended range by keeping the calories you burn close or equal to the calories you consume.

This energy-balance system, however, can easily be upset by the body’s reward system. When you do something that helps you survive – for example, eat a calorie-rich hamburger – your body sends your brain a shot of the feel-good neurotransmitter dopamine.

Such a system was beneficial for our hunter-gatherer ancestors. When they found a stash of honeycomb or made a big kill, for instance, the body’s reward system compelled them to overeat, which made sense for survival, as the next meal might not come for a while.

Today, however, this system doesn’t work in our favor. With constant access to high-fat, sugary foods, we can too easily overeat, which pushes our bodies’ reward system into a feel-good loop.

As a reaction to our overeating, we often put ourselves on diets. Yet, research suggests that if we diet repeatedly, it can cause changes in the brain, making the reward response even stronger, and resulting in even more indulgence.