A analysis of 121 weight loss studies, with over 21,000 participants, found that most diets failed after 12 months.

The study examined 14 different diets, from paleo to the Atkin's diet, and found that the lowered risk of heart disease and benefits of weight loss did not last a year.

"It doesn't really matter what diet you choose, the weight loss that you will get is not very different," study author Gordan Guyatt told Insider. "Diets, for most people, generally do not work. "

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A new analysis of 121 diet studies, examining the diets of over 21,000 people, found evidence to support something many experts have been saying for years: that strict diets don't work in the long-term.

In the paper, published in the British Medical Journal, the authors concluded that many of the 14 diets they examined resulted in improved blood pressure and an average weight loss of 10 pounds at six months.

But after a year of starting the diet, most of those weight loss benefits were gone and their lowered heart disease risk was back to where it had been — except for those adhering to the Mediterranean diet.

"The message is fairly clear," study author Gordan Guyatt, a professor at McMaster University, told Insider. "It doesn't really matter what diet you choose, the weight loss you will get is not very different. Diets, for most people, generally do not work. "

Some 69% of the 21,942 participants were women, with an average age of 49, with diets that lasted about six and a half months. Many of their diets were branded, like Weight Watchers to South Beach, while others were trend-based, like low fat or paleo diets.

"Lowering your blood pressure or your bad cholesterol, for a period of time, say six months, is not going to make any long term difference if it goes back up again," said Guyatt. "You have to have blood pressure and lipid lowering for years before it's really going to lower your risk of bad events like strokes and heart attacks."

This study is more evidence that diets don't work in the long term

Obesity levels worldwide have tripled since 1975. In tandem, America's diet industry has ballooned into a $72 billion behemoth, promising silver-bullet solutions to weight gain or persistent excess weight, without communicating the complexity of the matter.

"The study is reaffirming what we already knew," said Caroline Apovian, director of the Nutrition and Weight Management Center at Boston Medical Center. "It just adds to the evidence. It gives us reassurance with almost 22,000 patients that, yes, what we thought is actually the case."

Apovian pointed out that the study didn't tease out differences between the different diets as much as it could have, and that, given the study was an analysis of other studies, the authors had no way of examining if the participants actually ate what they said they ate.

She added that the Mediterranean diet emerged with a moderate victory in the study, as participants who did that omega-3-heavy diet seemed to retain a lowered risk of heart disease at the 12-month mark, unlike all the other diets.

Guyatt told Insider he couldn't offer any advice to people concerned about maintaining their weight.

"There is some evidence that is consistent with our results that we have genetic presets for a particular weight, at least in environments where we can get as much to eat as we want," he said. "There's nothing that we can confidently recommend people when it comes to diets. People must look to their own psychology and friends and family, knowing that it's going to be difficult."

For people who have difficulty sticking to their diets — and, according to the existing research, that's most people — Guyatt says they should take comfort in the notion that they are not alone.

"If it helps you feel less defeated when you can't keep the weight off to know that other people have exactly the same experience, then that is a good thing," said Guyatt. "I don't think we know what a healthy diet is. So picking something that feels healthy and satisfying is probably the best you can do at this point."

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