Assistant Professor Texas Woman's University Houston, Texas, United States
Disclosure(s):
Kimberly Townsend, MS, RD, LD: No relevant financial relationship(s) with ineligible companies to disclose.
Objectives: The objective of this study was to compare secular trends in BMI, body fat percent (BF%), BMI-defined obesity and BF%-defined obesity using data from the National Health and Nutrition Examination Survey (NHANES).
Methods: The cross-sectional analysis of the NHANES 1999 to 2006 and 2011 to 2018 consisted of 22,100 nationally representative sample of non-institutionalized adults between ages 20 and 59 years. Exclusions included pregnant women, amputations, missing height, missing weight, or missing dual energy x-ray absorptiometry (DXA) scans. Demographics (age, race/ethnicity, and gender) were self-reported. Height and weight were measured using stadiometer and digital scale. Body fat percentage was measured using DXA whole body scans. BMI-defined obesity was considered as having a BMI ≥ 30 kg/m2 and BF%-defined obesity as having a percent body fat ≥ 25% and ≥ 35% for men and women, respectively. All analyses accounted for the sampling design and used the appropriate sample weights and age-adjusted estimates. Multiple-imputation was used for the 1999-2006 DXA datasets per NHANES analytic guidelines. A p-value < 0.05 was considered statistically significant.
Results: BMI in men increased by about 1.4 kg/m2 (p trend = .002) from 1999 to 2018 yet body fat percent remained relatively stable from (27.1% to 27.3%, respectively; p trend =.711); however, BMI in women increased by about 0.7 kg/m2 (p trend = .003) yet body fat percent decreased from 1999 – 2018 (39.3% to 38.5%, respectively; p trend = .152). BMI- defined obesity in men increased by about 14 percentage points (pp) (p= .002) yet body fat percent-defined obesity remained relatively stable (1 pp increase) from 1999 – 2018 (p trend =.702). BMI- defined obesity in women increased by about 4.7pp (p trend =.011) yet body fat percent-defined obesity decreased (1.22 pp change) from 1999 – 2018 (p trend =.476). However, body weight has not increased significantly (0.05 kg) among men (p trend = .360), but has increased by approximately 0.16 kg per year among women (p trend = .006) from 1999-2018.
Conclusions: Body fat percent remained stable among men and decreased among women despite increasing BMI among both genders. Body fat percent may not be useful for estimating changes in body weight status among adults at the population level.
