Here’s why losing weight when you’re already thin is a bad thing

BOSTON — Losing weight is generally viewed as a healthy endeavor. Countless people set out each new year to shed extra pounds and tone up. However, researchers from the T.H. Chan Harvard School of Public Health report that intentionally trying to lose weight is something only obese people and those who medically need to slim down should do. This latest study finds weight loss attempts among lean individuals are associated with longer-term weight gain and a higher risk of type 2 diabetes.

On the other hand, after analyzing nearly 200,000 people, researchers report losing weight often results in long-term health benefits among obese individuals. People who lost more than 10 pounds had both a lower risk of type 2 diabetes and gained less weight back.

Studies show that obesity can lead to a higher risk of various health issues like diabetes. Controlling one’s weight is an effective way to prevent obesity and associated diseases, but long-term weight changes and diabetes risk fluctuations haven’t been well studied up until now.

So, researcher Qi Sun and colleagues examined collections of healthy participants from three prospective studies conducted between 1988 and 2017. Each person was between the ages of 24 and 78, and mostly female.

Strategies that successfully led to weight loss of more than 9.9 pounds were divided into seven categories: fasting, low-calorie diet, exercise, low-calorie diet plus exercise, commercial weight loss program, diet pills, and a combination of fasting, commercial, and diet pills (FCP).

Among those strategies, exercise was the most effective in terms of long-term weight control and prevention among people with obesity. It was also associated with the lowest levels of weight gain after a period of four years — 4.2 percent less overall average weight than at the start among individuals with obesity, 2.5 percent weight loss among overweight individuals, and 0.4 percent in lean people. However, this trend was reversed for the FCP strategy as individuals with obesity sustained 0.3 percent weight loss, overweight people experienced two percent more weight gain, and lean individuals gained 3.7 percent more weight.

Weight loss among lean people increases diabetes risk

Fast forward 24 years later, and diabetes risk among individuals with obesity was still lower, regardless of the person’s specific weight loss strategy. This trend ranged from a 21-percent risk drop among the exercise group to a 13-percent reduction for people using diet pills.

Regarding overweight individuals, the team found a range of nine percent reduction in type 2 diabetes risk for exercisers to a 42-percent increased risk among those who took pills. Among lean participants, astoundingly, all weight loss was associated with an increased risk of type 2 diabetes — ranging from a nine-percent increase among exercisers to a 54-percent increase for the pills or FCP groups.

In conclusion, study authors theorize that while weight loss is clearly a positive for those who are overweight or obese, weight loss strategies don’t result in the same benefits for lean individuals. They suggest that weight loss approaches should only be adopted by those who medically need them.

“We were a bit surprised when we first saw the positive associations of weight loss attempts with faster weight gain and higher type 2 diabetes risk among lean individuals,” Sun concludes in a media release. “However, we now know that such observations are supported by biology that unfortunately entails adverse health outcomes when lean individuals try to lose weight intentionally. Good news is that individuals with obesity will clearly benefit from losing a few pounds and the health benefits last even when the weight loss is temporary.”

The study is published in PLoS Medicine.

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