Have you recently tried cutting carbs? Eating like a caveman? Going vegetarian or gluten-free? Each of these diets has been all the rage in recent years, but there’s one big problem: None of them stick.
Why? Because diets are designed to fail.
At least that’s according to Traci Mann, a University of Minnesota psychologist and researcher who’s spent the last few decades studying peoples’ eating habits and was recently interviewed by the Washington Post.
Dieting, Mann told the Post, unleashes a series of biological changes in your body which make it “practically impossible to keep the weight off.”
In other words, if you’ve ever found yourself losing weight at the start of a diet and then felt dismayed by the fact that the pounds simply seemed to creep back on, it isn’t because you didn’t try hard enough.
On the contrary, it’s because diets are only structured to provide short-term benefits, not to help people keep weight off in the long term.
“For practically any diet…in that first 6 to 12 months, people can lose about 10% of their starting weight. So a 200 pound person will lose about 20 pounds in the short run. But the short run isn’t the whole story. Everyone acts like the short run is the whole story, and that anything that happens later is the dieter’s fault and not really part of the diet. People act like the only part that is the diet’s fault is the beginning bit. The long-term part, people always say that’s not the diet, that’s the person. And yet, it’s clear that that’s not true. It’s over the long term that you see all these biological changes take control.”
The biological changes are the real problem, says Mann. Here are some of the specific shifts she mentions that happen when you diet:
- Your brain becomes more aware of food. “Your brain becomes overly responsive to food, and especially to tasty looking food,” says Mann, “so the thing you’re trying to resist becomes harder to resist.”
- Your hormones levels change, often making you feel hungrier no matter how much you eat. “As you lose body fat, the amount of different hormones in your body changes,” Mann explains. “And the hormones that help you feel full, or the level of those rather, decreases. The hormones that make you feel hungry, meanwhile, increases. So you become more likely to feel hungry, and less likely to feel full given the same amount of food.”
- Your metabolism slows down, and more of what you eat gets stored as fat. When you diet, you’re effectively convincing your body that it is starving, Mann says. Your body responds by running as efficiently as possible (i.e. burning the fewest calories possible). This shift “would be good thing if you’re starving to death,” says Mann, “But it isn’t a good thing if you’re trying to lose weight.” She adds, “when your body finds a way to run itself on fewer calories there tends to be more leftover, and those get stored as fat, which is exactly what you don’t want to happen.”
All of Mann’s points are grounded in scientific research. A 2013 study comparing the brain scans of people who’ve dieted with those who haven’t, for example, found that dieters tended to show more of a response in the areas of their brains linked with processing rewards and less of a response in the parts of their brains linked with a sense of control. Hormone levels, too, can shift in response to diet, as can metabolism.
Still, this advice shouldn’t be taken as a doomsday scenario for people trying to lose weight.
Instead, it points out the problems with focusing entirely on changing what you eat rather than taking into account other behavioural patterns.
These include when you eat, how much you exercise, and whether or not your friends and family members support your health goals. These factors, often called “behaviour modification,” are the focus of programs like Weight Watchers, for example, and they work for thousands of people.
“Most of us know people — friends, family members, colleagues — who have lost weight and kept it off for years by changing the way they eat and boosting their physical activity,” writes David H. Freedman, a consulting editor at Johns Hopkins Medicine International, in a post for the Columbia Journalism Review. “They can’t all be freaks of biology.”
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