Belly fat raises heart failure risk even in people with normal BMI, study warns

A new study has found that abdominal fat is a stronger predictor of heart failure than body mass index, and that the risk applies even to people whose BMI falls within the normal range. The finding directly challenges a widespread assumption in clinical practice: that a normal weight on the scale means a person's cardiovascular risk is correspondingly low. It does not, at least not when that person is carrying a disproportionate amount of fat around their midsection.

This matters at a population level because BMI remains the default screening tool used in primary care to flag weight-related health risk. Millions of patients get a clean bill of health on that metric every year while carrying the specific fat distribution that this study links to elevated heart failure risk. They leave the doctor's office without any recommendation to address their abdominal fat because the standard measurement did not identify a problem.

What the study measured and how it was designed

The study used data from the UK Biobank, a large prospective cohort that has followed over 500,000 participants across the United Kingdom since recruitment began in 2006. Researchers analyzed body composition data including BMI, waist circumference, waist-to-hip ratio, and waist-to-height ratio alongside heart failure outcomes tracked over a median follow-up period of approximately twelve years. The analysis adjusted for age, sex, smoking status, physical activity, diabetes, and hypertension to isolate the independent contribution of abdominal fat to heart failure risk.

The researchers found that waist-to-height ratio was the strongest predictor of heart failure among all the body composition measures tested. Participants in the highest quartile of waist-to-height ratio had approximately twice the heart failure incidence of those in the lowest quartile, independent of their BMI classification. When the analysis was restricted to participants with a normal BMI between 18.5 and 24.9, elevated waist-to-height ratio still predicted significantly higher heart failure rates compared to normal-BMI participants with lower abdominal fat.

Why abdominal fat is metabolically different from fat elsewhere in the body

Not all fat tissue behaves the same way. Subcutaneous fat, which sits just beneath the skin, is relatively metabolically inactive. Visceral fat, which accumulates around internal abdominal organs including the liver, pancreas, and intestines, is metabolically active in ways that drive systemic disease. Visceral fat releases inflammatory cytokines including interleukin-6 and tumor necrosis factor-alpha, promotes insulin resistance, and contributes to elevated triglycerides and reduced HDL cholesterol. Each of those downstream effects independently increases cardiovascular risk.

For heart failure specifically, visceral fat accumulation is associated with two distinct pathways. The first is structural. Fat deposits around the heart muscle, called pericardial and epicardial fat, are directly associated with left ventricular dysfunction and diastolic impairment, which is the type of heart failure where the heart muscle stiffens rather than weakens. The second pathway runs through metabolic disturbance: insulin resistance and chronic low-grade inflammation from visceral fat promote fibrosis and oxidative stress in cardiac tissue over time.

The problem with relying on BMI as a cardiovascular screening tool

BMI was originally developed in the 1830s by Belgian mathematician Adolphe Quetelet as a population-level statistical tool, not a clinical diagnostic instrument for individual patients. It measures weight relative to height but captures nothing about where body fat is stored or what proportion of body mass is fat versus muscle. A person with substantial muscle mass and low body fat can have the same BMI as a person with low muscle mass and high abdominal fat. They face radically different cardiovascular risk profiles, but BMI treats them identically.

The phenomenon the study documents has a clinical name: metabolically obese normal weight, or MONW. People with MONW have BMIs in the normal range but carry enough visceral fat to produce the metabolic profile typically associated with obesity. A 2019 study published in the European Heart Journal estimated that approximately 20 to 30 million Americans fall into this category. They are disproportionately older adults and postmenopausal women, in whom fat tends to redistribute toward the abdomen even as total body weight remains stable.

What clinicians are being asked to change

The study's authors, along with cardiologists commenting on the findings in the European Heart Journal where the study was published, called for waist circumference and waist-to-height ratio measurements to become routine components of cardiovascular risk assessments in primary care. The current threshold for elevated risk in adults is a waist circumference above 88 cm (35 inches) in women and above 102 cm (40 inches) in men, according to American Heart Association guidelines. A waist-to-height ratio above 0.5 is the commonly cited threshold across multiple population studies, and it can be calculated with a tape measure and no specialist equipment.

Adding these measurements to routine visits does not require new technology or significant additional clinical time. A waist circumference measurement takes under thirty seconds. The barrier is not logistical. It is the inertia of clinical practice built around BMI as the primary body composition indicator, and the absence of formal guideline updates incorporating abdominal fat metrics into standard cardiovascular risk scores. The American Heart Association's PREVENT equation, updated in 2023 to include kidney function and metabolic variables, does not currently include waist circumference as a direct input. A formal guideline update incorporating abdominal fat measures is under discussion for the next revision cycle.