A new international study led by researchers from the Harvard T.H. Chan School of Public Health and Ben Gurion University in Israel has found that nearly one-third of people who followed a healthy diet did not lose weight—but still experienced major health benefits.
The findings challenge the common belief that weight loss is the only sign of health improvement and offer a more hopeful message for people who struggle to lose weight.
The study was published in the European Journal of Preventive Cardiology. It followed 761 adults in Israel who had abdominal obesity—a condition marked by excess belly fat. These participants were part of three well-known nutrition studies called DIRECT, CENTRAL, and DIRECT-PLUS.
All participants were randomly assigned to follow one of several healthy diets, including low-fat, low-carb, Mediterranean, or green-Mediterranean diets, for 18 to 24 months. The goal was not only to observe changes in body weight, but also to see what happened inside their bodies on a deeper metabolic level.
Surprisingly, while 36% of participants lost a significant amount of weight (more than 5% of their starting weight), and another 36% lost a smaller amount (up to 5%), about 28% lost no weight at all or even gained some. But despite not losing weight, many of those individuals still experienced important improvements in their health.
The research showed that people who didn’t lose weight still had better cholesterol levels—especially a rise in HDL, which is known as “good” cholesterol.
They also had lower levels of leptin, a hormone linked to hunger and fat storage, and they lost visceral fat—the kind of belly fat that wraps around organs and raises the risk of heart disease and diabetes. These changes mean their bodies became healthier, even if the number on the scale didn’t go down.
Lead author Dr. Anat Yaskolka Meir pointed out that our culture often links weight loss with success, but that’s not always the full picture. “We’ve been conditioned to equate weight loss with health, and weight-loss-resistant individuals are often labeled as failures,” she said.
“Our findings reframe how we define clinical success. People who do not lose weight can still improve their metabolism and reduce their long-term risk for disease. That’s a message of hope, not failure.”
The study also measured how each kilogram (2.2 pounds) of weight loss was connected to better health markers. For each kilogram lost, participants saw increases in good cholesterol, and drops in triglycerides, insulin, leptin, liver fat, and blood pressure. But even those who lost no weight still saw some of these changes, especially in hunger hormones and deep belly fat.
Interestingly, those who were “resistant” to weight loss were more likely to be older and women. The researchers noted that future studies should focus more on women to better understand their unique responses to diet.
In a particularly exciting discovery, the research team used advanced genetic tools to identify 12 DNA methylation sites that may predict whether someone will respond well to a diet in terms of weight loss. This means that people may be biologically wired to respond differently to the same diet—not because of lack of willpower, but because of differences in their genes and biology.
“This isn’t just about discipline—it’s about biology,” said Professor Iris Shai, a senior researcher in the study. “And now we’re getting close to understanding it.”
In short, this study changes how we think about dieting and health. Weight loss is not the only measure of success. Even when people don’t shed pounds, a healthy diet can still make a big difference in improving heart health, metabolism, and long-term disease prevention.
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The research findings can be found in the European Journal of Preventive Cardiology.
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