Boston, MA — A new international study has found that nearly one-third of people who followed a healthy diet saw no change in weight—but still experienced major health improvements. The research, led by scientists from the Harvard T.H. Chan School of Public Health and Ben-Gurion University in Israel, suggests that weight loss is not the only sign of better health.
Even without shedding pounds, participants in the study showed key improvements in their metabolic health. These included higher levels of HDL (the “good” cholesterol), reduced leptin (a hormone that controls hunger), and a drop in visceral fat—the deep belly fat that surrounds organs.
“We’ve been taught to link health with weight loss, and those who don’t lose weight are often seen as failing,” said lead author Dr. Anat Yaskolka Meir, a postdoctoral fellow at Harvard Chan School. “But our research shows that people can improve their metabolism and reduce long-term health risks even without losing weight. That’s a hopeful message.”
The findings were published June 5 in the European Journal of Preventive Cardiology.
The research analyzed data from 761 people in Israel with abdominal obesity who took part in three workplace-based nutrition trials: DIRECT, CENTRAL, and DIRECT-PLUS. These trials, which lasted 18 to 24 months, asked participants to follow one of several healthy diets—including low-fat, low-carb, Mediterranean, or green-Mediterranean options.
Of the participants, 36% lost more than 5% of their starting weight, another 36% lost up to 5%, and 28% lost no weight or gained some. While weight loss was linked to several health benefits—including lower insulin, triglycerides, and liver fat—the study also found that those who didn’t lose weight still saw many of the same improvements.
These “weight loss-resistant” individuals, who were often older or women, still gained more HDL, produced less leptin, and reduced visceral fat.
“These are deep metabolic changes with real health effects,” Yaskolka Meir said. “A healthy diet can improve your body’s function—even if the scale doesn’t move.”
The team also used advanced genetic analysis tools and found 12 DNA methylation markers that could predict how likely a person is to lose weight long-term.
“This discovery points to a biological basis for why some people respond better to diets than others,” said Dr. Iris Shai, the study’s senior author and principal investigator of the trials. “It’s not just about motivation—it’s also about genetics and biology.”
The researchers acknowledged one limitation: most of the participants were men. They noted that future research should include more women to better understand gender differences.
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