The BMI vs Body Fat Debate: Study Suggests One-Third of People with Normal BMI are Obese

Analysis of anthropometric data of 3000 individuals in Israel found that one-quarter of men and more than one-third of women whose body mass index (BMI) was in the “normal” range were classified with excess adiposity.¹ Further, levels of key clinical parameters of the metabolic syndrome were elevated in this cohort of normal-weight individuals with obesity (NWO), including triglycerides, LDL-C, and total cholesterol.¹

Their findings lead researchers from the faculty of medicine at the School of Public Health at Tel Aviv University (TAU) to conclude that greater adiposity, measured as percentage of body fat (BF%), is a far more reliable indicator of health and particularly of cardiometabolic risk than BMI; they recommend that the measure ultimately be turned into the gold standard for obesity assessment.¹

"Israel is a leader in childhood obesity and more than 60% of the country's adults are defined as overweight,” said lead study author Prof Yftach Gepner, in a TAU statement.² “The prevailing index in this respect is BMI, based on weight and height measures, which is considered a standard indicator of an individual's general health. However, despite the obvious intuitive connection between excess weight and obesity, the actual measure for obesity is the body's fat content, with the maximum normal values set at 25% for males and 35% for females.” He adds that the result of the disparity between the 2 indices, BMI and adiposity, is identified as “the paradox of obesity with normal weight,”¹ or more simply, the obesity paradox.

The investigators point out, further, that “the use of BMI to identify excess fat at the individual level has reasonable specificity but poor sensitivity, with approximately half the individuals with excessive body fat percentage (BF%), misclassified as non-obese.”¹ Their study was designed to identify the prevalence of metabolically obese normal weight individuals (NWO) in a sample of the Israeli population and to investigate the relationship between NWO, NW lean (NWL), and cardiometabolic risk.¹

Gepner’s team recruited study participants from an Israeli nutrition clinic between 2015 and 2021 for the cross-sectional study. Candidates were required to be age 20 years or older and no BMI value was specified. Investigators recorded values for weight, abdominal circumference (ABC), and BMI. They utilized dual X-ray absorptiometry (DEXA) to measure body composition. The researchers tapped medical records for serum markers of glycemic control, lipids, liver enzymes, and blood count. For their analyses, Gepner et al applied multivariate linear regressions to assess associations between cardiometabolic markers in NWL vs NWO participants, stratified by gender, and adjusted to age and BMI. Using nonlinear regression, they also analyzed the relationship between BMI and BF%.

Excess adiposity was defined as ≥25% for men and ≥ 35% for women.

FINDINGS

The final cohort numbered 3001 participants of which approximately half were men and half women (51.9% and 48.1%, respectively), according to the results. Body weight was in the normal range (BMI 18.5–24.9 kg/m²) for 967 (32.2%) of participants, a group comprised of 326 men (mean age 36.1 years) and 641 women (mean age 34.7 years). Body fat distribution in this group ranged from 4% to 49%.

NWO. Within this group, 26% of men and 38% of women had BF% above the specified cutoff for excess adiposity. The researchers noted a contrast between this group and those in the overweight BMI category (BMI25-29.9 kg/m²), where 69.6% of men and 88.8% of women were above the cutoff. They also point out the converse in this instance, ie, that approximately 30% of the men and 10% of women in the overweight BMI category could be classified as having normal BF%

TG, LDL-C, TC. When they compared clinical parameters that would indicate risk for cardiometabolic disease between NWL and NWO participants, they reported that men with NWO had elevated levels of:

• Triglycerides (76.5 vs 101.2 mg/dL; P= .004)
• LDL-C (103.3 vs 107 mg/dL; P=.011)
• Total cholesterol (171.5 vs 190.2 mg/dL; P=.007)

Among women with NWO, however, the only statistically significant difference observed was that triglycerides were higher among among those with NWO (BF% ≥35) than among those with normal BMI/low BF% (101.4 vs 84 mg/dL; P=.03).

Age, ABC. Gepner et al found no significant association between age groups and NWO across age strata, but they did find similar associations between age strata and cardiometabolic risk for each gender. Among NWO, the team reported higher ABC in 60% of women (≥88 cm) vs just 4% of men (≥102 cm).

Gepner says that NWO appears to be much more common in Israel than his group had thought. The finding concerns him given that those within the normal range of the “prevailing BMI index usually pass 'under the radar,'” being overlooked for treatment or counseling on lifestyle and behavior change, thus increasing their risk for cardiometabolic diseases.²

Limitations of their study cited by the authors include the cross-sectional design, which precludes any inference of causality, and the study’s single-center source of participants, which limits the ability to generalize findings beyond that cohort. Also, the researchers did not have access to additional data regarding metabolic syndrome.

References
1. Lahav Y, Kfir A, Gepner Y. The paradox of obesity with normal weight; a cross-sectional study. Front Nutr. 2023;10:1173488. doi:10.3389/fnut.2023.1173488 https://www.frontiersin.org/articles/10.3389/fnut.2023.1173488/full

2. One third of normal-weight individuals are obese. News release. Tel Aviv University. July 12, 2023. Accessed July 12, 2023. https://www.eurekalert.org/news-releases/995313