Patterns of lifetime reported physical activity and their association with BMI and body composition in USA adults.

Background: Physical activity (PA) has a direct influence on body composition, particularly in terms of lean body mass (LBM) and fat mass (FM). This study assesses how lifelong changes in PA impact body mass index (BMI) and body composition using data from NHANES (1999-2006) for adults aged 29 to 59 years.

Methods: Data were extracted from the National Health and Nutrition Examination Survey (1999-2006), including male and female participants aged 29-59. The cross-sectional analysis focused on the relationship between BMI and the fat mass index (FMI)/Lean Body Mass Index (LBMI) ratio, adjusted for height (ht). Multivariate linear regression models were adjusted for covariates and stratified by sex. All analyses were adjusted considering the sample weights.

Results: The analysis comprised 5115 participants, with 51.7% male and an average age of 42.8±0.13 years. The FMI/ht-LBMI ratio is approximately 0.4 for men and 0.7 for women. The results indicated that women had a mean BMI increase (β=1.9, 95% CI: 1.4-2.4) for every 0.1 increase in the FMI/ht-LBMI ratio, while men had a mean BMI increase (β=1.0, 95% CI: 0.7-1.4) (P<0.05), compared to those maintaining the same PA pattern over ten years. Additionally, factors such as socioeconomic status, race/ethnicity, and nutritional status at age 25 were found to significantly impact body composition outcomes.

Conclusions: In summary, long-term PA emerges as a modifier in population-level body composition. Individuals with a history of lower PA over the last decade showed a higher proportion of adipose tissue. In this way, the importance of maintaining substantial levels of PA throughout life is emphasized, contributing positively to body composition.