Effect of frequent interruptions of sedentary time on nutrient metabolism in sedentary overweight male and female adults

Abstract

This study compared 24-h nutrient oxidation responses between a sedentary condition (SED) and a condition in which short 5-min bouts of moderate-intensity physical activity were performed hourly for nine consecutive hours over 4 days (MICRO). To determine whether any shifts in fuel use were due solely to increases in energy expenditure, we also studied a condition consisting of a single isoenergetic 45-min bout of moderate-intensity exercise (ONE). Twenty sedentary overweight or obese adults (10 men/10 women; 32.4 ± 6.3 yr; BMI, 30.6 ± 2.9 kg/m2) completed all three conditions (MICRO, SED, and ONE) in a randomized order. Each condition consisted of a 3-day free-living run-in followed by a 24-h stay in a whole-room calorimeter to measure total energy expenditure (TEE) and substrate utilization. Dietary fat oxidation was also assessed during the chamber stay by administering a [1-13C] oleic acid tracer at breakfast. Energy intake was matched across conditions. Both MICRO and ONE increased TEE relative to SED, resulting in a negative energy balance. HOMA-IR improved in both activity conditions. MICRO increased 24-h carbohydrate oxidation compared with both ONE and SED ( P < 0.01 for both). ONE was associated with higher 24-h total fat oxidation compared with SED, and higher 24-h dietary fat oxidation compared with both SED and MICRO. Differences in substrate oxidation remained significant after adjusting for energy balance. In overweight and obese men and women, breaking up sitting time increased reliance upon carbohydrate as fuel over 24 h, while a single energy-matched continuous bout of exercise preferentially relies upon fat over 24 h. NEW & NOTEWORTHY Insulin sensitivity, as assessed by HOMA-IR, was improved after 4 days of physical activity, independent of frequency and duration of activity bouts. Temporal patterns of activity across the day differentially affect substrate oxidation. Frequent interruptions of sedentary time with short bouts of walking primarily increase 24-h carbohydrate oxidation, whereas an energy-matched single continuous bout of moderate intensity walking primarily increased 24-h fat oxidation.

Trial registration: ClinicalTrials.gov NCT02258438.

Keywords: carbohydrate oxidation; dietary fatty acid oxidation; microbouts of activity; physical inactivity; whole-room calorimetry.

Figures

Fig. 1.

Trial Consolidated Standards of Reporting Trials diagram.

Fig. 2.

Protocol of the study day in the whole-room calorimeter. SED, sedentary condition in which participants remained sedentary (no exercise); ONE, one bout condition in which participants remained sedentary for the day except for completing one bout of moderate-intensity treadmill walking for 45 min; MICRO (microbouts) condition in which participants remained sedentary for the day except for completing nine bouts of 5-min moderate-intensity treadmill walking once an hour for nine consecutive hours. CTRC, Center of University of Colorado Hospital; FFM, fat-free mass. ■ indicates 45-min bout of walking; ▌ indicates 5-min walking bout; ↑indicates blood collection; and solid arrowhead indicates meals.

Fig. 3.

Absolute and relative 24 h nutrient oxidation, balance, and dietary fat oxidation. A: energy intake (MJ/day), energy expenditure (MJ/day), and energy balance (MJ/day) during the study day in the whole room calorimeter. B: relative contribution (%) of carbohydrate (CHO), fat (FAT), and protein (PRO) oxidation to total 24-h energy expenditure. C: absolute nutrient oxidation (g/day) for CHO, FAT, and PRO. D: 24-h nonprotein respiratory quotient for each study condition: sedentary (SED), one bout (ONE), and microbouts (MICRO). E: 24-h dietary fat oxidation (percent dose recovery from 1-13C oleic acid stable isotope tracer) for each study condition: SED, ONE, and MICRO. Data are presented as means ± SE. *P < 0.05, **P < 0.01, ***P < 0.001.

Fig. 4.

Waking and sleeping substrate oxidation. Absolute and relative substrate oxidation during waking (0800–2230) and sleeping (2230–0630) time. A: relative contribution (%) of carbohydrate (CHO), fat (FAT), and protein (PRO) oxidations to waking energy expenditure (EE). B: waking absolute nutrient oxidation (grams) of CHO, FAT, and PRO oxidations for waking energy expenditure. C: waking energy expenditure. D: relative contribution (%) of CHO, FAT, and PRO oxidations to sleeping energy expenditure. E: sleeping absolute nutrient oxidation (grams) of CHO, FAT, and PRO oxidations for sleeping energy expenditure. F: sleeping energy expenditure. %EE, percent contribution to energy expenditure. Data are presented as means ± SE. *P < 0.05, **P < 0.01, ***P < 0.001.

Fig. 5.

Twenty-four hour- and active-period incremental area under the curves (iAUCs) for plasma metabolites. iAUCs for plasma glucose, triglycerides (TG), insulin, and free fatty acids (FFAs) measured during the inpatient study day. A: 24-h and active-period plasma glucose iAUCs. B: 24-h and active-period plasma TG iAUCs. C: 24-h and active-period plasma insulin iAUCs. D: 24-h and active-period FFA iAUCs. Active period iAUC measured from the first to the last microbout of activity (1000–1800). SED, sedentary exposure; ONE, one bout (45 min of moderate intensity at 1000) walking exposure; MICRO, microbout exposure (5-min walking per hour for nine consecutive hours at moderate intensity from 1000 to 1800). Data are presented as means ± SE. ***P < 0.001.