Research Article: Temporal trends in obesity defined by the relative fat mass (RFM) index among adults in the United States from 1999 to 2020: a population-based study
Abstract:
Objectives The body mass index (BMI) largely underestimates excess body fat, suggesting that the prevalence of obesity could be underestimated. Biologically, women are known to have higher body fat than men. This study aimed to compare the temporal trends in general obesity by sex, ethnicity and age among adults in the USA using the relative fat mass (RFM), a validated surrogate for whole-body fat percentage and BMI. Design Population-based study. Setting US National Health and Nutrition Examination Survey, from 1999–2000 to 2017–March 2020. Participants A representative sample of adults 20–79 years in the USA. Main outcome measures Age-adjusted prevalence of general obesity. RFM-defined obesity was diagnosed using validated cut-offs to predict all-cause mortality: RFM?40% for women and ?30% for men. BMI-defined obesity was diagnosed using a cut-off of 30?kg/m 2 . Results Analysis included data from 47?667 adults. Among women, RFM-defined obesity prevalence was 64.7% (95% CI 62.1% to 67.3%) in 2017–2020, a linear increase of 13.9?percentage points (95% CI 9.0% to 18.9%; p<0.001) relative to 1999–2000. In contrast, the prevalence of BMI-defined obesity was 42.2% (95% CI 39.4% to 45.0%) in 2017–2020. Among men, the corresponding RFM-defined obesity prevalence was 45.8% (95% CI 42.0% to 49.7%), a linear increase of 12.0?percentage points (95% CI 6.6% to 17.3%; p<0.001). In contrast, the prevalence of BMI-defined obesity was 42.0 (95% CI 37.8% to 46.3%). The highest prevalence of RFM-defined obesity across years was observed in older adults (60–79 years) and Mexican Americans, in women and men. Conversely, the highest prevalence of BMI-defined obesity across years was observed in middle-age (40–59 years) and older adults, and in African American women. Conclusions The use of a surrogate for whole-body fat percentage revealed a much higher prevalence of general obesity in the USA from 1999 to 2020, particularly among women, than that estimated using BMI, and detected a disproportionate higher prevalence of general obesity in older adults and Mexican Americans.
Introduction:
The prevalence of obesity (excess body fat) in the USA has doubled from 15.0% in 1976–1980 to 30.9% in 1999–2000, 1 and it continues to increase. 2 3 The age-adjusted prevalence of obesity among adults in the USA has been estimated at 41.9% in 2017–March 2020. 4 Obesity diagnosis is based on the body mass index (BMI), an indirect measure of body fat. 5 6 BMI is calculated as the ratio of body weight in kilograms to the square of the height in metres. 7 BMI does not distinguish between fat mass and fat-free mass…
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