(P20-054-25) Unhealthy Lean Phenotypes Prevalence in Normal Weight Adults in the United States

Objectives: This study examines the prevalence of unhealthy lean phenotypes, including normal weight obesity (NWO), normal weight central obesity (NWCO), and metabolically unhealthy normal weight (MUNW) among normal-weight adults in the United States.

Methods: Data from the National Health and Nutrition Examination Survey (NHANES) 2011–2018 were analyzed in adults aged 20–84 years with a normal body mass index (BMI) of 18.5–24.9 kg/m². NHANES is a continuous, nationally representative cross-sectional survey of noninstitutionalized U.S. population, where each participant represents ~50,000 individuals through assigned sample weights. Normal weight lean (NWL) had normal body fat percentage (BF%) which was defined as < 25% for men and < 35% for women, and normal waist circumference (WC) which was defined as < 102 cm for men and WC < 88 cm for women; NWO was defined as high BF% ≥25% in men and ≥35% in women; NWCO was defined as having high WC ≥102 cm in men and ≥ 88 cm in women; and MUNW was defined as meeting of ≥2 criteria (other than WC) in the National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP-III) for metabolic syndrome. Overlapping phenotypes were studied including NWO+NWCO, NWO+MUNW, NWCO+MUNW and NWO+NWCO+MUNW. Appropriate weights were used and prevalence was reported as weighted percentages with 95% confidence intervals. All analyses were conducted using Stata version 17.0.

Results: For the 1,555 participants with a normal BMI, the mean age was 37.96±10.21 years and the mean BMI was 22.37±1.39 kg/m². Among those, 802 (53.62%) were classified as healthy lean, representing approximately 9.69 million US adults, 34.63% were NWO (~6.26 million), 8.05% were NWCO (~1.45 million), and 19.58% were MUNW (~3.54 million). Both NWO and NWCO were present in 3.29% of participants (~595,000), while 8.28% had both NWO and MUNW (~1.49 million), and only 0.5% had NWCO and MUNW (~90,000). Only 1.91% of participants (~345,000) had all three phenotypes: NWO, NWCO, and MUNW. 

Conclusions: Unhealthy lean phenotypes are commonly observed in individuals with a normal BMI. These results suggested that BMI is not a complete measure of health and that health risks should be assessed using other methods aside from weight.

Funding Sources: This study is supported by the Startup Funds from the University of Mississippi.