A new study led by researchers from Harvard T.H. Chan School of Public Health and Israel’s Ben-Gurion University reveals that nearly one-third of individuals who adopt and maintain a healthy diet do not lose weight but still experience significant health benefits. Beyond weight loss, participants showed notable improvements in cardiometabolic markers, including increased levels of high-density lipoprotein cholesterol (HDL, the “good” cholesterol), reduced leptin levels (a hormone signaling hunger), and decreased visceral fat (deep abdominal fat often surrounding organs).
“We have long equated health success with weight loss, often stigmatizing those who struggle to lose weight as failures,” said lead author Anat Yaskolka Meir, a postdoctoral researcher in epidemiology at Harvard T.H. Chan School of Public Health. “Our findings redefine clinical success: even those who do not lose weight can improve their metabolism and reduce long-term disease risk. This delivers hope, not failure.”
The study was published on June 5 in the European Journal of Preventive Cardiology.
Researchers analyzed weight and health changes in 761 abdominally obese Israeli participants who took part in three well-controlled workplace nutrition clinical trials — DIRECT, CENTRAL, and DIRECT-PLUS — with high adherence and comprehensive metabolic assessments. Participants were randomly assigned to follow various healthy diets, including low-fat, low-carbohydrate, Mediterranean, and green Mediterranean diets for 18 to 24 months.
Across all trials and diets, 36% of participants achieved clinically significant weight loss (defined as over 5% reduction of initial weight); 36% achieved moderate weight loss (under 5% reduction); and 28% struggled to lose weight or gained weight. Weight loss correlated with multiple health improvements: for each kilogram lost, HDL cholesterol increased by 1.44%, triglycerides decreased by 1.37%, insulin dropped by 2.46%, leptin decreased by 2.79%, liver fat reduced by 0.49 units, and blood pressure and liver enzymes also declined.
However, the study also found that participants who did not lose weight — typically older adults and/or women — experienced many of the same metabolic benefits. Their HDL cholesterol levels improved, leptin levels decreased, reducing hunger, and harmful visceral fat was reduced.
“These are profound metabolic changes with real impact on cardiometabolic health,” Yaskolka Meir said. “Our research shows that a healthy diet is effective even without weight loss.”
Using advanced omics tools, researchers identified 12 DNA methylation sites that strongly predict long-term weight loss.
“This new discovery suggests that some individuals may have inherent biological differences in their response to the same diet,” said corresponding author and chief investigator of the nutrition trials, Iris Shai, adjunct professor of nutrition at Harvard T.H. Chan School of Public Health. “It’s not simply a matter of willpower or discipline — it’s biology. And we are beginning to understand it.”
The study acknowledged limitations, noting that most participants were male. Researchers emphasized that future studies should focus more on female populations.
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