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Why diets don't work


New diets come out every year, each claiming to be the end-all solution to lose weight, but as one expert argues, all are short-term solutions that have long-term negative effects on one’s body and mind.

Traci Mann, a professor of health and social psychology at the University of Minnesota, joined “Take Care” to talk about diets -- what they are and why they fail.

Mann, who is also the principal investigator of the Mann Lab, a health and eating laboratory at the University of Minnesota, said dieting has been around since at least the 1950s. Fad diets have brought us everything from the grapefruit diet to the cabbage soup diet, but Mann said no matter the type of diet, they’re all harmful.

For one, the diets just don’t work, Mann said, as most people that do lose weight on any diet gain all the weight back over time.

“That’s why I say diets don’t work,” she said. “It’s not really worth it to put yourself through the trouble of dieting if the weight’s just going to come back on anyway.”

Mann said the reason diets fail is because of both psychology and biology. Mann, through her research, has learned about how flimsy a person’s self-control becomes when they’re on a diet.

“There is no better place to study self-control failures than in the eating of dieters,” Mann said. “We’ve learned that pretty much anything you do to a dieter messes them up, and over all this time, … I never found anything that made a dieter better at resisting some tempting food that’s right in front of them.”

On the biological side of things, a person’s body will change with their diet. If the body starts to detect that not as many calories are coming in, the body starts to undergo many biological changes that make it harder to maintain the diet.

“Calorie deprivation leads to hormone changes that make you feel hungry given the same amount of food that didn’t used to make you still feel hungry,” she said. “So, if you’re going to feel hungry after eating what normally would make you feel full, it’s going to be harder to keep dieting.”

In addition, metabolism changes mean a person would have to eat less and less to see the same rate of weight loss as time goes on.

"Most people notice that you can lose weight on a diet. ... What people don't realize is that that tends to come back."

“You have to consume fewer calories than you were consuming at the beginning of your diet to lose weight, so if you keep eating what you were eating at the beginning of your diet, … after a while, your metabolism will change, and you’ll stop losing weight given that same amount of calories,” Mann said.

Dieting also contributes to stress, which Mann said is prohibitive to maintaining a healthier lifestyle.

“Restricting eating leads to this stress response, and stress … leads to all kinds of negative health effects throughout your body,” she said. “So, if dieting leads to stress, that’s a really big problem.”

On top of that, stress can make it more likely for people to gain weight.

“Dieting is almost undermining itself by leading to stress,” she said.

And just following a diet can be stressful, especially when socializing at restaurants or parties.

“Most people, when they’re on diets, find it very unpleasant,” she said. “They feel like they’re missing out on foods other people are eating. … In my view, you’re better off not dieting than dieting and instead just doing some generally healthy behaviors.”

Because of dieting’s restrictive nature, there is the concern that it could lead to an eating disorder. Mann said that causal question is hard to answer.

“Clearly, anorexia needs to start with weight loss,” Mann said. “There’s clearly going to be dieting in the beginning of it, but that doesn’t mean dieting is a cause of anorexia. … There is evidence that repeated dieting can lead overtime to binge eating, so that is a connection I’m more comfortable [making].”

Despite all the negative effects of dieting, diets remain a popular mainstay in popular culture. Mann said this pervasiveness is because of many reasons, the first being that people are too focused on the short-term weight loss to worry about long-term weight gain.

“Most people notice that you can lose weight on a diet,” she said. “What people don’t realize is that that tends to come back.”

And when that weight comes back, people put the blame in the wrong place -- themselves instead of the diet.

“Since most people blame the weight regain on themselves and give the credit of weight loss to the diet, that makes people more likely to keep dieting again,” Mann said. “They think, ‘Oh, this time, I’ll do it better.’”

Another reason diets stay popular is because there is a small percentage for whom dieting does work, and people think they’ll be in that minority.

“That’s great that people are optimistic and hopeful and motivated, but most people are not going to be in that small minority for whom it works,” she said.

In Mann’s book, “Secrets from the Eating Lab,” she mentions that, rather than losing weight to look better, people should try to reach their “leanest livable weight.” She said this is the lowest weight a person can be without doing any kind of diet.

“Basically, people’s weight wants to be in a certain range, … and to live below that range is really difficult,” Mann said. “You have to heavily restrict your eating and watch it all the time, and I don’t think that is a worthwhile thing for people to try to do, which is why, instead, I encourage them to live within that set range but at the low end of it.”

While Mann’s model is effective, she said many people aren’t satisfied with the leanest livable weight and instead want to be thinner. Mann said if a person is looking to reach that leanest livable weight, though, there are strategies to get there.

One big one Mann outlined was “veggies first,” where a person eats a vegetable before putting any other food out on the table or on their plate. When a person typically tries to consume vegetables, it’s as a side next to their main dish, and that makes a person far more likely to skip eating them altogether in favor of eating the better option.

“Vegetables aren’t as tempting and they’re not considered as delicious as certain unhealthier foods,” she said. “This strategy came about as a way to put vegetable eating in a competition that it could win, and the competition that a vegetable could win is vegetable versus nothing.”

Mann said that the advantage of leanest livable weight is that it’s still within a range the body wants to be in, so it’s far easier to maintain that weight without experiencing any of the negative psychological or biological effects of dieting. And the best way to get there is to change your habits and the circumstances that trigger you to consume unhealthy foods.

“If we can change that circumstance, it helps us without us needing to really think it through very much,” she said.