Metabolic Implications of Diet and Energy Intake during Physical Inactivity

Abstract

Purpose: Physical inactivity is associated with disruptions in glucose metabolism and energy balance, whereas energy restriction may blunt these adverse manifestations. During hypocaloric feeding, higher-protein intake maintains lean mass which is an important component of metabolic health. This study determined whether mild energy restriction preserves glycemic control during physical inactivity and whether this preservation is more effectively achieved with a higher-protein diet.

Methods: Ten adults (24 ± 1 yr) consumed a control (64% carbohydrate, 20% fat, 16% protein) and higher-protein diet (50% carbohydrate, 20% fat, 30% protein) during two 10-d inactivity periods (>10,000 → ~5000 steps per day) in a randomized crossover design. Energy intake was decreased by ~400 kcal·d to account for reduced energy expenditure associated with inactivity. A subset of subjects (n = 5) completed 10 d of inactivity while consuming 35% excess of their basal energy requirements, which served as a positive control condition (overfeeding+inactivity).

Results: Daily steps were decreased from 12,154 ± 308 to 4275 ± 269 steps per day (P < 0.05) which was accompanied by reduced V˙O2max (-1.8 ± 0.7 mL·kg·min, P < 0.05), independent of diet conditions. No disruptions in fasting or postprandial glucose, insulin, and nonesterified fatty acids in response to 75 g of oral glucose were observed after inactivity for both diet conditions (P > 0.05). Overfeeding+inactivity increased body weight, body fat, homeostasis model assessment of insulin resistance, and 2-h postprandial glucose and insulin concentrations (P < 0.05), despite no changes in lipid concentrations.

Conclusions: We show that independent of diet (normal vs higher-protein), mild energy restriction preserves metabolic function during short-term inactivity in healthy subjects. That is, metabolic deterioration with inactivity only manifests in the setting of energy surplus.

Trial registration: ClinicalTrials.gov NCT03013764.

Figures

Figure 1.. Experimental design and physical activity/energy expenditure.

Healthy physically active adults (n=10) defined as exceeding 10,000 steps per day, completed A) two periods of physical inactivity while consuming either a Control diet or Higher-protein diet in a randomized cross-over design. Average B) daily steps and C) energy expenditure (total and physical activity). Data are means ± SEM. Two-way ANOVA with activity and diet as factors was used for statistical comparisons. Post hoc comparisons with Tukey correction were run when a significant main effect was observed. *P<0.05 vs Active. Horizontal arrows represent the number of days for a given data assessment, whereas vertical arrows indicate testing on a single day in the laboratory. Days 1–10 were ‘free-living’. White bars reflect the ‘active’ phase and gray bars represent the ‘inactive’ period. OGTT, oral glucose tolerance test; FMD, flow-mediated dilation; CGMS, continuous glucose monitoring system; BP, blood pressure; DEXA, dual x-ray absorptiometry; EE, energy expenditure. n=10/condition.

Figure 2.. Effect of physical inactivity on glucose tolerance and indices of insulin sensitivity/resistance in response to a Control diet and Higher-protein diet.

Physically active and physically inactive A) glucose, B) insulin, and C) NEFA curves with corresponding 3-h AUC (inset) following a 75-g oral glucose challenge during the Control diet and Higher-protein diet conditions. D) Two-hour glucose and E) two-hour insulin during the OGTT. F) HOMA-IR. Data are means ± SEM. *P<0.05 vs Active. Two-way ANOVA with activity and diet as factors was used for statistical comparisons. Post hoc comparisons with Tukey correction were run when a significant main effect was observed. AUC, area under the curve; NEFA, nonesterified fatty acids; HOMA-IR, homeostasis model assessment of insulin resistance. n=10/condition.

Figure 3.. Effect of physical inactivity on glucose tolerance and indices of insulin sensitivity/resistance in response to overfeeding.

Physically active and physically inactive A) glucose, B) insulin, and C) NEFA curves with corresponding 3-h AUC (inset) following a 75-g oral glucose challenge during hypercaloric feeding. D) Two-hour glucose and E) two-hour insulin during the OGTT. F) HOMA-IR. Data are means ± SEM or presented as induvial responses. *P<0.05 vs Active; #P=0.055 vs Active. Paired-samples t tests were run to compare Active and Inactive. White circles are ‘active’ phase and gray circles are ‘inactive’ period. AUC, area under the curve; NEFA, nonesterified fatty acids; HOMA-IR, homeostasis model assessment of insulin resistance. n=5/condition.