Physical Activity and Sedentary Time: Association with Metabolic Health and Liver Fat

Abstract

Introduction/purpose: To investigate whether (a) lower levels of daily physical activity (PA) and greater sedentary time accounted for contrasting metabolic phenotypes (higher liver fat/presence of metabolic syndrome [METS+] vs lower liver fat/absence of metabolic syndrome [METS-]) in individuals of similar body mass index and (b) the association of sedentary time on metabolic health and liver fat.

Methods: Ninety-eight habitually active participants (53 female, 45 male; age, 39 ± 13 yr; body mass index 26.9 ± 5.1 kg·m), underwent assessments of PA (SenseWear armband; wear time ~98%), cardiorespiratory fitness (V˙O2 peak), body composition (magnetic resonance imaging and magnetic resonance spectroscopy) and multiorgan insulin sensitivity (oral glucose tolerance test). We undertook a) cross-sectional analysis comparing four groups: nonobese or obese, with and without metabolic syndrome (METS+ vs METS-) and b) univariate and multivariate regression for sedentary time and other levels of PA in relation to liver fat.

Results: Light, moderate, and vigorous PA did not account for differences in metabolic health between individuals, whether nonobese or obese, although METS+ individuals were more sedentary, with a higher number, and prolonged bouts (~1-2 h). Overall, sedentary time, average daily METS and V˙O2 peak were each independently associated with liver fat percentage. Each additional hour of daily sedentary time was associated with a 1.15% (95% confidence interval, 1.14%-1.50%) higher liver fat content.

Conclusions: Greater sedentary time, independent of other levels of PA, is associated with being metabolically unhealthy; even in habitually active people, lesser sedentary time, and higher cardiorespiratory fitness and average daily METS is associated with lower liver fat.

FIGURE 1

Cardiometabolic phenotyping, individual participant plots for: V˙O₂ peak relative to FFM (A), whole-body insulin sensitivity (B), hepatic insulin resistance index (C) and liver intrahepatocellular lipid (IHCL) (D). Data are presented as mean ± SD. Gray circles, METS−; white circles, METS+; nonobese are grouped left and obese are grouped right. *P < 0.05 group difference between BMI category, further group differences being given in the text.

FIGURE 2

Habitual PA and sedentary time, individual participant plots for: average daily steps (A), nonsleep sedentary time (<1.5 METS) (B), light activity (1.5–3 METS) (C), moderate to vigorous activity (>3 METS) (D), daily metabolic equivalents (METS) (E) and PA duration (F). Data are presented as mean ± SD. Gray circles, METS−; white circles, METS+; nonobese are grouped left and obese are grouped right. *P < 0.05 group difference between BMI category, further group differences being given in the text.

FIGURE 3

Nonsleep sedentary behavior, individual participant plots for: duration of sedentary bouts (A) and number of sedentary bouts in given bout category (B) between 1 and 2 h. Data are presented as mean ± SD. Gray circles, METS−; white circles, METS+; nonobese are grouped left and obese are grouped right. *P < 0.05 group difference between BMI category, further group differences being given in the text.