Beyond BMI: Why Body Fat Percentage May Be a Better Measure of Obesity

BMI has been the standard metric used to define overweight and obesity for decades. It is simple, fast, and widely used in clinical settings. But new research in body composition estimation suggests that moving from BMI to more direct measures, such as body fat percentage (BF%), could improve how we assess and manage obesity (Potter et al., 2024).

This article explains the difference between BMI and BF%, why BF% may be more accurate, and what new BF% thresholds could mean for defining overweight and obesity.

Quick definition: BMI vs BF%

BMI (Body Mass Index)

A weight-to-height ratio used to classify weight status.

BF% (Body Fat Percentage)

A measure of how much of your body is made up of fat.

They are not the same thing. Two people can have the same BMI and very different body compositions.

 

Section 1: Understanding BMI

BMI is calculated by dividing a person’s weight in kilograms by the square of their height in metres (kg/m²) (National Heart, Lung, and Blood Institute, 2023).

BMI categories used in clinical practice:

Underweight: BMI < 18.5

Normal weight: BMI 18.5–24.9

Overweight: BMI 25–29.9

Obesity: BMI ≥ 30

Healthcare professionals often use BMI as a screening tool to estimate body fat and assess weight-related health risks. It is convenient, but it has important limitations (Nuttall, 2015).

Where BMI can fall short

1. It does not distinguish fat mass from muscle mass or bone mass.

2. It does not reflect where fat is stored in the body.

3. It can be less accurate for athletes, older adults, or certain ethnic groups.

That is why BMI can misclassify people. Someone with high muscle mass may be labelled overweight or obese despite having low body fat. Another person may fall into a “normal” BMI range while carrying a high level of body fat and associated health risks.

A key criticism is also historical. BMI was introduced almost two centuries ago by a Belgian mathematician and was not originally designed as a medical diagnostic tool.

How big can the gap be?

A recent study by Visaria et al. (2023) compared obesity prevalence using BMI and BF% and found a striking difference:

By BMI: 36% of adults classified as obese

By BF%: 74% of adults classified as obese

 

Section 2: The case for body fat percentage (BF%)

BF% directly measures the proportion of fat in the body. It gives a clearer picture of body composition by separating fat mass from lean mass. Practical ways to estimate BF% are becoming more accessible and more accurate, including: Bioelectrical impedance analysis (BIA)

BIA estimates fat mass by sending a low electrical current through the body and analysing how it passes through different tissues (Lyons-Reid et al., 2020).

Skinfold measurements

This method uses callipers to measure skinfold thickness at different sites to estimate subcutaneous fat (Silveira et al., 2020).

DEXA scan (dual-energy X-ray absorptiometry)

DEXA uses low-dose X-rays to distinguish bone, fat tissue, and lean mass. It provides precise measurements of BF% and bone density (Chaves et al., 2022; Laskey, 1996).

Section 3: New BF% thresholds for overweight and obesity

Recent research suggests clinically meaningful BF% cut-offs for overweight and obesity may be:

For men

Overweight: 25% body fat

Obesity: 30% body fat

For women

Overweight: 36% body fat

Obesity: 42% body fat

These thresholds reflect sex-based differences in body composition and aim to better capture unhealthy fat accumulation (Potter et al., 2024).

Section 4: Why BF% may be the better metric

More direct measurement

BF% measures fat itself, which is the tissue most closely linked to many obesity-related risks.

Closer link to health outcomes

BF% thresholds are tied to the prevalence of metabolic syndrome, a key obesity-related comorbidity that includes cardiovascular risk.

More personalised

BF% accounts for differences in muscle mass and body composition that BMI cannot.

Sex-specific thresholds

Men and women can be assessed using thresholds that reflect real biological differences.

More health-focused

BF% aligns more closely with outcomes such as cardiometabolic risk, which is directly influenced by excess body fat.

Section 5: Limitations to keep in mind

No universal global agreement

There is not yet full consensus on BF% thresholds across different populations.

Age and sex variation

BF% changes naturally with age and differs by sex, which can require separate reference ranges.

Measurement sensitivity

Some methods, especially BIA, are influenced by hydration, recent food intake, and physical activity, which can affect accuracy.

Conclusion

Recent evidence suggests that shifting from BMI to BF% could be a major step forward in how overweight and obesity are defined and managed. With proposed thresholds of 25% and 36% BF for overweight in men and women, and 30% and 42% for obesity, health professionals may be able to offer more precise, personalised strategies for obesity management.

As body composition tools continue to improve and become more accessible, BF% is increasingly positioned as a preferred measure for evaluating and managing obesity (Potter et al., 2024).

References

Chaves, L.G.C. de M., et al. (2022). Assessment of body composition by whole-body densitometry: what radiologists should know. Radiologia Brasileira, 55, 305–311. doi:10.1590/0100-3984.2021.0155-en.

Jayedi A, et al. (2020). Central fatness and risk of all cause mortality: systematic review and dose-response meta-analysis of 72 prospective cohort studies. BMJ. 2020;370.

Laskey, M.A. (1996). Dual-energy X-ray absorptiometry and body composition. Nutrition, 12(1), 45–51. doi:10.1016/0899-9007(95)00017-8.

Lyons-Reid, J., et al. (2020). Bioelectrical Impedance Analysis—An Easy Tool for Quantifying Body Composition in Infancy? Nutrients, 12(4). doi:10.3390/nu12040920.

National Heart, Lung, and Blood Institute (2023). Calculate your BMI.

Nuttall, F.Q. (2015). Body Mass Index. Nutrition Today, 50(3), 117–128. doi:10.1097/nt.0000000000000092.

Potter, A.W., et al. (2024). Defining Overweight and Obesity by Percent Body Fat instead of Body Mass Index. The Journal of Clinical Endocrinology and Metabolism, dgae341. doi:10.1210/clinem/dgae341.

Silveira, E.A., et al. (2020). Body fat percentage assessment by skinfold equation, bioimpedance and densitometry in older adults. Archives of Public Health, 78(1). doi:10.1186/s13690-020-00449-4.

Visaria, A., et al. (2023). Prevalence of Obesity Based on Body Fat Percentage vs. Body Mass Index. Presented at ENDO 2023, Endocrine Society annual meeting, Chicago, IL.