Redefining diet success: Experts say weight not the only measure of better health

A significant portion of people who adopt and stick to a healthy diet may not lose weight. However, they may still experience meaningful health benefits indicative of holistic wellness, including cardiometabolic benefits, according to a new study.

The study analyzed data from 761 adults with abdominal obesity who participated in a series of high-profile, workplace-based nutrition trials in Israel. Despite following healthy diets such as low-fat, low-carbohydrate, and Mediterranean variations for up to two years, nearly 30% of participants did not lose weight — yet saw improvements in key markers of metabolic and cardiovascular health.

“We have been conditioned to equate weight loss with health, and weight loss-resistant individuals are often labeled as failures,” says lead author Anat Yaskolka Meir, postdoctoral research fellow in the Department of Epidemiology at the Harvard T.H. Chan School of Public Health and Ben Gurion University in Israel. “Our findings reframe how we define clinical success.”

“People who do not lose weight can improve their metabolism and reduce their long-term risk for disease. That’s a message of hope, not failure.”

More than a number on the scale

Published in the European Journal of Preventive Cardiology, the results show that 36% of participants achieved clinically significant weight loss — more than 5% of their body weight — and another 36% lost some weight, 28% were classified as weight-loss resistant. These individuals, often older and more likely to be women, either maintained their weight or gained slightly.

Yet, the researchers point out that even these non-responders experienced health improvements. They had increased high-density lipoprotein (HDL), or “good” cholesterol, lower levels of the hunger hormone leptin, and significant reductions in visceral fat — the deep belly fat linked to a higher risk for heart disease and type 2 diabetes.

For participants who did lose weight, the study quantified notable benefits. Each kilogram lost was associated with a 1.44% increase in HDL cholesterol, a 1.37% drop in triglycerides, and reductions in insulin, leptin, liver fat, blood pressure, and liver enzymes.

However, the metabolic gains in weight-stable individuals challenge the prevailing notion that diet success must be defined by weight loss alone.

“These are deep metabolic shifts with real cardiometabolic consequences,” Meir underscores. “Our study showed that a healthy diet works, even when weight doesn’t shift.”

Genetics and diet response

The team also used advanced omics tools to analyze genetic factors influencing weight response. The team says they identified 12 DNA methylation sites that strongly predict long-term weight loss, potentially opening doors for future personalized nutrition strategies.

Still, the researchers acknowledge the study’s limitations — such as having a majority-male participant pool — and call for additional research, especially focused on women and other underrepresented populations.

Moreover, the research team says the findings highlight the importance of redefining success in dietary interventions, particularly as interest in personalized nutrition and metabolic health continues to rise.

“This novel finding shows that some people may be biologically wired to respond differently to the same diet,” concludes corresponding author Iris Shai, the principal investigator of the nutrition trials and adjunct professor of nutrition at the Harvard Chan School. “This isn’t just about willpower or discipline — it’s about biology, and now we’re getting close to understanding it.”