Abstract MP026: Effects of Substituting Sedentary Behavior With Light and Moderate-to-vigorous Physical Activity on Obesity Indices in Adults

Abstract

Sedentary behavior (SB) has emerged as an independent risk factor for the occurrence of cardiovascular problems and all-cause mortality. However, the deleterious effect of SB may be a consequence of replacing time spent in light and moderate-to-vigorous (MVPA) physical activities. Few studies have explored this topic, especially in prospective follow-up studies with adults. We hypothesized that substituting SB with light and MVPA may be associated with 1-year change in body weight, body mass index (BMI) and fat body mass (FBM) in asymptomatic adults. We aimed to use isotemporal substitution modeling to investigate cross-sectional and longitudinal effects of reallocating SB with light and MVPA on obesity indices in asymptomatic adults. Also, we examined the correlations between 1-year changes in physical activity intensity categories (i.e., sedentary, light, moderate, vigorous, very vigorous, and MVPA) and changes in FBM. We included 780 participants over the age of 20-yr. Body weight, BMI, and FBM (bioelectrical impedance), as well as its 1-year changes, were the outcomes. We objectively measured physical activity using triaxial accelerometers (ActiGraph GT3X) worn above the dominant hip during waking hours for at least four consecutive days (4-7 days). After 1-year follow-up, 242 completed all the assessments. We reallocated time spent in SB by light or MVPA and assessed the cross-sectional and prospective associations with the outcomes. The cross-sectional isotemporal substitution analysis showed that substituting 10-min blocks of SB with MVPA was significantly related to decreases of 1.23 kg in body weight, 0.30 kg/m2 in BMI and 0.38% in FBM. Substituting 10-min blocks of SB with light physical activity produced significant lower values of body weight (1 kg) and BMI (0.1 kg/m2). We found no effects of substituting SB with light physical activity on FBM. As for the longitudinal analysis, we observed that reallocating SB with MVPA was only associated with a significant decline in FBM (-0.31%). We found no other significant effects of substituting SB with light or MVPA. We observed significant correlations between change in FBM and changes in sedentary (r = 0.147), light (r = -0.290) and vigorous (r = -0.277) physical activity. After stepwise multiple regressions adjusted for all physical activity intensities and covariates, change in vigorous physical activity was the only intensity selected as a significant predictor for 1-year absolute change in FBM (β = -0.312; ΔR 2 = 0.102). We may conclude that SB presents non-consistent influence on obesity indices in asymptomatic adults and its substitution with MVPA is associated with significant improvement in body composition over a short-term follow-up. Our results suggest that vigorous physical activities play the most important role in obesity in adults.