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The science is clear: fad diets don't work

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There are all sorts of popular diets out there. Atkins. Weight Watchers. Zone. South Beach. Paleo. Bulletproof. Americans spend some $60 billion a year in pursuit of the magic formula that will finally help them shed extra pounds for good.

There's just one problem. Scientists can't find evidence that any of these highly restrictive diets work very well over the long term.

Recently a team of Harvard-affiliated researchers tried to sift through all the best available evidence and see whether low-fat diets — in which 30 percent or fewer calories came from fat — work better than those that are higher in fat (including low-carb). What they found was that all diets seemed to be equally ineffective.

In the study, published today in the journal Lancet, the typical weight loss was about 7 pounds — an amount that researchers consider insignificant because most study participants were overweight or obese to begin with, and intended to lose many pounds. What's more, the dieters were only followed for a year, and the researchers noted that most people regained the weight after that. All this despite "concerted efforts among motivated clinical trial participants and staff," the authors wrote.

The results are so abysmal, in fact, that doctors are now at a loss about what specific advice they should give people who want to lose weight. "Practically, the study tells us what we shouldn't be doing," says lead author Deirdre Tobias, a doctor at Brigham and Women’s Hospital and Harvard Medical School. "But," she added, "we don't conclude with what we should be doing."

That squares with the findings of other high-quality studies that compare different diets and find people lose only a few pounds long term no matter what they try.

"All diets lead to unimpressive weight loss after one year," Kevin Hall, a researcher at the National Institutes of Health, told Vox. "People tend to be fine for the first three to six months, then plateau their body weight, and then regain the weight for the next few months."

Never diet

Dr. Tobias said her research suggests that people need to look beyond restricting certain macronutrients (like fat or protein or carbohydrates) and instead try to incorporate healthy foods into their diets. That's the direction some countries are going in with their dietary guidelines, and it squares with the advice I've gotten from just about every diet expert I've ever spoken to.

But eating that way won't necessarily lead to miraculous weight loss, either. Hall pointed out that there's little high-quality evidence that "whole food diets" work for weight loss, and, more important, people have a lot of difficulty sticking to new eating patterns of any kind over the longer term. "What seems to be clear is that long-term diet adherence is abysmal, irrespective of whether low-fat or other diets, such as low-carbohydrate diets, are prescribed," he wrote in a Lancet commentary related to the study.

There is, however, lots of evidence that what you eat matters for health, and poor diets impact everything from your risk of cancer and heart disease to your overall risk of death.

So there are probably two logical ways to proceed. First, ignore the propaganda about fad diets. The science is clear: They don't work. Second: Do as Tobias and other obesity researchers suggest, and incorporate healthy foods into your diet in a way you like and can maintain. You may not dramatically alter your figure, but at least you'll do your body a favor, and you'll never need to eat a low-fat muffin or kale salad again.

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