Dieting when you’re not obese can actually do more harm than good, a new study suggests.
A study done by Harvard University found that people who are already thin that lost 10 pounds had a higher risk of developing type 2 diabetes a decade later — and were also more likely to gain weight later in life.
Researchers collected data for 200,000 healthy Americans — 90% of which were female — between 1988 and 2017. Participants were divided into three categories by body mass index: healthy or underweight, overweight and obese. They were then split into two groups: those who lost 9.9 pounds over four years and those who did not.
Seven more subgroups were created within those going on a diet based on how they chose to lose weight: low-calorie dieting, exercising, low-calorie diet plus exercise, fasting, commercial weight loss programs, diet pills and a combination of fasting, commercial programs and diet pills.
After observing medical records over 10 years on average, scientists found that lean people who went on an extreme diet gained between 4.4 and 17 more pounds than their peers — but obese people who participated in four of the programs (low-calorie diet, exercise, low-calorie diet plus exercise and fasting) lost between 3.5 and 1.3 more pounds than their peers.
When looking at the risk of diabetes, researchers found that thinner people who lost a significant amount of weight were 54% more likely to get type 2 diabetes later on, and the obese adults who went on a strict diet were less likely to develop diabetes.
“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,” said Dr. Qi Sun, an epidemiologist at Harvard who led the study.
“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.”
Results also showed that skinny people who lose weight by following a trendy diet or weight loss program were expected to gain a lot of weight later in life, likely because the weight loss leads to biological changes.
The scientists believe that lean people who lost a lot of weight had higher levels of hunger hormones, leading them to crave more junk food and causing the body to accumulate more fat cells in order to boost the hormone levels. They also suspect that dramatic weight loss leads to lower levels of anorexigenic hormones that suppress hunger.
Researchers are now warning that weight loss diets should be reserved only for those who “medically need them” — not for already thin people who hope to achieve a body that lives up to Instagram standards.
“The 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,” Sun said.