What matters more when losing your belly fat?

BEER-SHEVA, Israel, March 5, 2025 – Not all fat is created equal when it comes to weight loss and health. While subcutaneous fat—the fat stored just under the skin—can be neutral or even beneficial, visceral fat is a different story. This deep belly fat, which surrounds vital organs like the liver, pancreas, and intestines, is a major driver of heart disease, diabetes, and chronic inflammation. Visceral fat and subcutaneous fat differ not only in location but also in metabolic activity. Visceral fat, stored deep within the abdominal cavity around major organs, is highly metabolically active and contributes to insulin resistance, inflammation, and increased cardiovascular risk. In contrast, subcutaneous fat, located just beneath the skin, serves as an energy reserve, and may even have protective properties in some cases. Studies show that visceral fat releases higher amounts of free fatty acids and pro-inflammatory cytokines, directly affecting liver metabolism and systemic inflammation, whereas subcutaneous fat contributes less to these metabolic disturbances.

But here’s where it gets interesting: even people with the same weight or BMI can have vastly different amounts and distributions of visceral fat. Some may carry a high absolute volume of visceral fat, while others may have a higher proportion of visceral fat compared to total abdominal fat. This raises a crucial question: When losing weight, is it more important to reduce the absolute amount of visceral fat, or does lowering its proportion matter more?

According to Prof. Iris Shai, the study’s principal investigator from Ben-Gurion University of the Negev, an adjunct professor at Harvard T.H. Chan School of Public Health, and an honorary professor at Leipzig University, Germany, these findings challenge the traditional focus on weight loss as a simple numbers game: “For clinicians, dietitians, and researchers, these findings offer a new framework for evaluating weight-loss success—one that considers not just how much fat is lost, but what kind of fat is lost and how it affects metabolic health. As precision nutrition and personalized medicine evolve, these results could pave the way for more effective interventions that help people achieve better long-term health outcomes.”

Hadar Klein, RD MSc, a doctoral student and lead author, explains the clinical significance: “Two people with the same BMI can have entirely different metabolic risks based on how their visceral fat is distributed. Our research shows that these differences matter when assessing cardiometabolic health risks.”

Dr. Hila Zelicha, RD PhD, co-lead author of the study, underscores the importance of tailoring weight-loss interventions to individual fat distribution patterns: “Understanding visceral fat dynamics could lead to more effective strategies. People with a high visceral fat proportion may benefit from different dietary and exercise approaches compared to those with a large absolute visceral fat area.”

BMI and total weight loss have been the go-to metrics for assessing health improvements for decades. But this study clarifies that it’s time to go beyond the scale. These findings underscore the importance of a personalized approach to weight loss and metabolic health. Precision medicine, which tailors interventions based on an individual's genetic, metabolic, and lifestyle characteristics, could enhance the effectiveness of dietary and exercise strategies. Understanding distinct adiposity phenotypes—individuals with high visceral fat proportion despite a lower BMI—may allow for more targeted prevention strategies against diabetes, cardiovascular disease, and metabolic syndrome. Future research should focus on refining clinical tools to identify and manage these high-risk individuals, ultimately moving beyond traditional weight-centric approaches to a more nuanced understanding of metabolic health.

In the groundbreaking new study, published in BMC Medicine researchers pooled data from two 18-month randomized controlled trials (DIRECT-PLUS and CENTRAL), analyzing 572 participants before and after weight loss dietary interventions. This study is one of the largest MRI-based weight-loss studies ever conducted. By using state-of-the-art MRI technology, researchers were able to precisely measure changes in both absolute visceral fat and its proportion relative to total abdominal fat, providing insights into how visceral fat dynamics impact cardiometabolic health.

Before Weight Loss: What Matters at Baseline? Even before shedding pounds, researchers discovered that the proportion of visceral fat (compared to total abdominal fat) was a stronger predictor of high triglyceride levels, a significant marker of metabolic dysfunction. Meanwhile, the absolute amount of visceral fat was more closely tied to chronic inflammation (CRP) and blood sugar regulation (HbA1c), both of which are key indicators of diabetes risk. It means that an individual with a lower waist circumference but a higher proportion of visceral fat is likely to have higher triglyceride levels than someone with a larger waist but a lower proportion of visceral fat. Additionally, an increased absolute mass of visceral fat is associated with greater inflammation and a higher risk of diabetes.

During Weight Loss: How Do Different Types of Fat Loss Affect Health? Over 18 months, study participants lost an average of 22.5% of their absolute visceral fat area. However, not all visceral fat loss had the same impact on health: Both absolute and proportional reductions in visceral fat led to significant improvements in triglyceride levels, blood sugar control, and liver function. Losing absolute visceral fat was more strongly associated with reducing leptin levels and insulin resistance, which is critical for preventing metabolic diseases like diabetes.

To determine whether absolute or proportional visceral fat loss had a more substantial impact on health, researchers conducted multiple statistical analyses, including regression models adjusted for age, sex, and baseline weight.

The trials were conducted at Ben-Gurion University of the Negev, Israel, together with researchers from Harvard, Leipzig, and Tulane and in collaboration with the Dimona Nuclear Research Center and Soroka University Medical Center.

This work was supported by grants from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), the Israel Ministry of Health, the Israel Ministry of Science and Technology, and the California Walnuts Commission. None of the funding providers participated in any stage of the study's design, conduct, or analysis, and they had no access to the study results before publication.