What proportion of individuals with a normal Body Mass Index (BMI) are considered obese based on their body fat percentage?

From the Guidelines

Approximately 20-30% of individuals with a normal Body Mass Index (BMI) are considered obese based on their body fat percentage, a condition known as normal weight obesity. This occurs when a person has a BMI within the normal range (18.5-24.9) but has an excessive amount of body fat that meets obesity criteria (generally >25% for men and >35% for women) 1. Normal weight obesity is important to recognize because these individuals face similar metabolic risks as those with traditional obesity, including increased risk of cardiovascular disease, metabolic syndrome, and insulin resistance, despite appearing to have a healthy weight by BMI standards.

Key Points to Consider

• BMI only measures the relationship between height and weight without distinguishing between fat mass and lean mass, which can lead to misclassification of individuals with normal weight obesity 1.
• Someone with low muscle mass but high body fat can have a normal BMI while still carrying unhealthy levels of adipose tissue.
• More accurate assessments of body composition, such as DEXA scans, bioelectrical impedance analysis, or skinfold measurements, are needed to identify these individuals who might otherwise be overlooked in routine medical screenings that rely solely on BMI.
• The limitations of BMI, including poor sensitivity in diagnosing excess body fatness, especially in some populations, must be considered when it is used alone as an index of adiposity in clinical practice 1.

Implications for Clinical Practice

• Healthcare providers should be aware of the potential for normal weight obesity and consider using additional measures of body composition to assess adiposity-related risk in individuals with normal BMI.
• Early identification and intervention can help mitigate the metabolic risks associated with normal weight obesity, improving overall health outcomes and quality of life.

From the Research

Proportion of Individuals with Normal BMI who are Obese by Body Fat Percentage

• According to a study published in 2008 2, approximately 43.9% of men and 52.3% of women with a normal Body Mass Index (BMI) were considered obese based on their body fat percentage.
• The study found that a BMI cutoff of ≥30 kg/m² had good specificity but missed more than half of people with excess fat, highlighting the limitations of using BMI as a measure of obesity.
• Another study published in 2012 3 found that BMI overestimated adiposity in men and underestimated adiposity in the elderly, suggesting that gender- and age-specific thresholds should be considered when using BMI to indicate adiposity.

Body Fat Percentage Thresholds for Obesity

• A study published in 2024 4 determined that the percentage body fat (%BF) thresholds for obesity were 30% for men and 42% for women, which corresponded to the existing BMI thresholds for obesity.
• The study found that using %BF thresholds instead of BMI could provide a more accurate measure of obesity and related health risks.
• The same study also found that individuals with a normal BMI (18.5-24.9 kg/m²) could still have a high percentage of body fat, highlighting the importance of using direct measures of adiposity to manage obesity-related disease.

Limitations of Using BMI to Measure Obesity

• A study published in 1995 5 found that waist circumference was a better indicator of health risk than BMI, as it could identify individuals with central fat distribution and high body mass index.
• Another study published in 2019 6 found that physical activity, sedentary activity, and food intake affected waist circumference and obesity prevalence among adults, but the relationship was unclear.
• The study suggested that further research was needed to understand the differences between the sexes in how physical and sedentary activity and food consumption were associated with obesity.