Normal BMI may hide excess body fat in 26% of men

A recent study indicates that having a normal Body Mass Index (BMI) does not necessarily equate to low body fat levels. Researchers found that approximately one-quarter of men in their sample who fell within the normal BMI range possessed fat percentages exceeding the threshold defined for excess adiposity. This finding suggests that the scale can obscure significant health risks related to body composition.

Study details on hidden fat

The research involved 3,001 adults aged between 20 and 95 years, all of whom underwent body composition assessments alongside tests for cardiovascular and metabolic health markers. Among these participants, 967 individuals were classified within the normal BMI range, defined as values between 18.5 and 24.9.

Within this specific cohort, 26 percent of men and 38 percent of women exhibited high body fat percentages according to the study's criteria. These thresholds were set at 25 percent or more for men and 35 percent or more for women. The data showed that elevated body fat correlated with increased blood markers, including triglycerides in both genders, as well as total and harmful cholesterol levels in men.

It is important to note that this was a cross-sectional study, capturing measurements at a single point in time. Consequently, it does not establish causality between excess fat and these blood changes, nor does it predict future mortality risks. Furthermore, the results do not imply that every person with a normal weight globally faces life-threatening dangers, nor that a slim appearance always masks a health issue.

Distinguishing obesity types

The concept of "normal weight obesity" describes the coexistence of a normal BMI with high body fat percentage. This differs from central obesity, which specifically refers to fat distribution around the abdomen. While these conditions can overlap, they are not synonymous. Additionally, a high body fat percentage alone does not confirm muscle weakness.

Therefore, relying solely on weight or body shape is insufficient for determining overall health status. A separate analysis involving 15,184 adults, followed for an average of nearly 14 years, examined mortality risks associated with these conditions. This study linked central obesity, measured by waist-to-hip ratio, to higher death rates among people with normal weights.

The analysis estimated that a man with a BMI of 22 and central obesity faced a relative increase in mortality risk of 87 percent compared to a man with the same BMI but without central obesity.

Guidelines for better assessment

To address these nuances, guidelines from the National Institute for Health and Care Excellence recommend using the waist-to-height ratio alongside BMI to assess central obesity in adults with a BMI under 35. For accurate measurement, the tape should be placed midway between the bottom of the ribs and the top of the hip bones. The reading is taken after a natural exhalation, and the waist circumference is then divided by height using the same unit.

The guidance advises keeping waist circumference below half of one's height. However, this metric serves as a risk estimation tool rather than a standalone diagnosis. The ultimate goal is to achieve a more comprehensive health evaluation, avoiding reliance on weight alone or pursuing unnecessary weight loss.