Even with a Normal BMI, Belly Fat May Sharply Raise Heart Disease Risk, Global Study Warns

A new international analysis reveals that millions of people considered to have a “healthy weight” are still at significant risk for heart disease, diabetes, and other metabolic illnesses due to hidden abdominal fat. The findings, published October 17, 2025, in JAMA Network Open, challenge long-standing reliance on Body Mass Index (BMI) as the primary tool for assessing obesity risk, and reinforce calls to incorporate waist circumference as a vital sign in routine clinical practice.​

Hidden Risk Behind “Normal” BMI

The global cross-sectional study led by Dr. Kedir Y. Ahmed, MPH, PhD, of the Rural Health Research Institute (Orange, New South Wales, Australia), analyzed data from 471,228 adults across 91 countries participating in the World Health Organization’s STEPwise surveys (2000–2020). Surprisingly, more than one in five adults with a normal BMI — defined as 18.5–24.9 — were found to have abdominal obesity, meaning excess visceral fat concentrated around the abdomen.​

These individuals showed significantly higher rates of hypertension, diabetes, elevated cholesterol, and triglycerides compared with peers of similar weight but without central fat accumulation. “People with normal BMI but abdominal obesity are often overlooked for appropriate interventions,” Dr. Ahmed told Medscape Medical News. “BMI and waist circumference should be used together, not in isolation, to provide a more complete cardiometabolic risk assessment”.​

Abdominal Fat: The Metabolic Threat Within

Visceral adiposity — the fat surrounding internal organs — is now recognized as a major independent driver of metabolic disease. According to Medscape Reference, excess abdominal fat increases cardiovascular mortality up to four-fold and is strongly linked with insulin resistance and inflammatory processes leading to heart disease.​

Traditional BMI screening often fails to capture these dangers because BMI reflects total body mass, not fat distribution. Someone with “normal” weight can still harbor visceral fat that disrupts metabolic function, putting them at risk for type 2 diabetes, fatty liver disease, and cardiovascular events.

Dr. Ahmed’s study echoes prior recommendations from professional bodies such as the 2020 International Consensus on Waist Circumference Measurement, which urged clinicians to treat waist size as a vital sign akin to blood pressure. Thresholds associated with sharply increased cardiovascular risk are over 94 cm for men and 80 cm for women, figures that vary slightly across ethnicities.​

Second Study Suggests New Ways to Define Obesity

A companion study, also published in JAMA Network Open on October 15, 2025, examined data from more than 250,000 participants in the U.S.-based All of Us (AoU) research program. It found that more than one-quarter of Americans lacked obesity under traditional BMI measures but met alternative criteria based on elevated waist-to-hip or waist-to-height ratios — a profile termed “anthropometric-only obesity”.​

Lead author Dr. Steven K. Grinspoon, Professor of Medicine at Harvard Medical School and Chief of the Metabolism Unit at Massachusetts General Hospital, noted that these findings redefine obesity as a functional, not purely weight-based, condition. “There’s a clear metabolic cost to having excess visceral fat even if the scale looks normal,” Grinspoon told Medscape. “We need to think beyond the BMI box.”

Interestingly, the researchers observed a more than 70% higher risk of developing type 2 diabetes among those with this “hidden obesity,” along with elevated risk for cardiovascular events and all-cause mortality.​

Expert Reactions and Clinical Perspective

Dr. Francesco Rubino, Professor of Metabolic and Bariatric Surgery at King’s College London and chair of the Lancet Commission on Obesity, cautioned against discarding BMI entirely. “BMI should still be used as a screening tool,” he said. “However, confirmation of obesity requires clear evidence of excess adiposity — particularly when BMI is between 30 and 40. We are not recommending labeling normal-BMI individuals as having obesity”.​

Independent cardiologist Dr. Meera Patel from AIIMS-Delhi, who was not involved with the study, describes the results as “a public health wake-up call.” She added, “In India and other South Asian populations, people tend to accumulate visceral fat at lower BMIs. Waist measurements and metabolic testing should become routine, especially for patients whose weight seems deceptively normal.”

Implications for Public Health and Policy

The findings have profound implications for global heart disease prevention, particularly in regions where non-communicable diseases (NCDs) such as diabetes and hypertension are already soaring. Current obesity rates, based solely on BMI, likely underestimate the true at-risk population.

Public health strategies focusing only on weight reduction may miss millions who would benefit from lifestyle or pharmacologic interventions targeting visceral fat.

Emerging drugs such as tesamorelin, a synthetic growth hormone analog approved for HIV-related lipodystrophy, are being studied for their ability to reduce visceral fat without major weight changes. Dr. Grinspoon suggested that “future therapies could target fat distribution rather than overall weight,” particularly in this under-recognized subgroup.​

Study Limitations and Next Steps

Both studies are observational, meaning they cannot establish causation. Differences in waist measurement methods and regional body composition norms may also affect precision. However, the uniformity of outcomes across multiple populations lends strong epidemiological weight to the findings.

Future longitudinal research, experts say, should explore how combining BMI, waist metrics, and imaging-based measures such as CT and DEXA scans can improve cardiometabolic risk prediction.

What Readers Should Take Away

For individuals, the message is simple but crucial: even if your BMI is normal, your waist size matters. Waist circumference is easy to measure — halfway between the lower rib and the iliac crest — and provides powerful insight into your metabolic health.

Doctors suggest combining a balanced diet, regular aerobic and resistance exercise, adequate sleep, and stress management to reduce central fat accumulation.

As Dr. Ahmed emphasized, “We need to move beyond weight stigma and anthropometric simplicity toward a more personalized view of metabolic health.”

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