Displacement Of Objectively Measured Sedentary Time With Light Physical Activity Was Associated With A Less Harmful Ectopic Fat Distribution In African Ancestry Men

Introduction: Ectopic fat is an established risk factor for cardiometabolic disorders. Few studies have examined the associations between objectively measured physical activity and ectopic fat depots, with mixed results. Here, we sought to use Isotemporal Substitution Framework to cross-sectionally model the displacement of sedentary time with physical activity and determine its association with simultaneously measured ectopic fat depots among Black Caribbean men from the Tobago Health Study. Hypothesis: Replacing sedentary time with physical activity will be cross-sectionally associated with less abdominal subcutaneous adipose tissue and ectopic adipose tissue around abdominal organs (visceral adipose tissue), and within abdominal muscle (intermuscular adipose tissue), the pericardium, and the liver (measured by liver density, where greater density indicates less fat). Methods: At the 2014-2016 visit, physical activity was assessed using the SenseWear Pro armband (worn for ≥4 days) and categorized as sedentary (<1.5 metabolic equivalents; METs), light activity (≥1.5 to <3.0 METs), or moderate-to-vigorous activity (≥3.0 METs). Computed tomography scans of the chest, abdomen, and liver were used to assess several ectopic fat depots. We used Isotemporal Substitution Framework, a technique to model the time-substitution effects of one physical activity over another, paired with linear regression to examine associations between physical activity and fat depots, separately, while adjusting for age, height, total awake time, and multiple comparisons using a Bonferroni correction. Results: On average, participants (n=271) were 63 years old (standard deviation, SD: 8) with a body mass index of 29 kg/m 2 (SD: 5), took 5,440 steps daily (SD: 2,959), and had 11.2 hours of sedentary behavior (SD: 3 hours), 4.5 hours of light physical activity (SD: 2 hours), and 54 minutes of moderate-to-vigorous physical activity per day (SD: 52 mins). Replacing 1 hour of sedentary time with light physical activity was cross-sectionally associated with 0.25 SD lower abdominal subcutaneous fat, 0.22 SD lower abdominal visceral fat, 0.10 SD lower abdominal intermuscular fat, 0.17 SD lower pericardial fat, and 0.14 SD higher liver density (i.e., less liver fat; all p-values≤0.001). Whereas, replacing sedentary time or light physical activity with moderate-to-vigorous physical activity were not significantly associated with adipose tissue in any depots. Conclusion: The displacement of sedentary time with light physical activity was significantly associated with a less harmful distribution of ectopic fat among this cohort of Black Caribbean men ages 50-89. Interventions focused on increasing light physical activity, rather than higher intensity activities, throughout the day may be more successful at reducing harmful ectopic adiposity since they may be easier to adhere to and maintain.