Abstract
Background: Metabolic syndrome and sarcopenia are physical conditions that are addressed differently through nutrition and exercise. Proteins, particularly branched-chain amino acids (BCAAs), exert insulinotropic effects, whereas exercise reduces insulin secretion. It is thus necessary to understand the effects of protein intake and exercise alone and in combination when considering suitable dietary and exercise therapies for treating metabolic syndrome and sarcopenia.
Methods: Seven healthy young-adult male volunteers participated in a crossover trial consisting of two 6-day experiments. Days 1-3 comprised a body-weight-maintained adjustment period during which the participants consumed a control diet (energy, 2,500 kcal; protein, 61.3 g for an individual weighing 60 kg). Days 4-6 comprised the treatment period during which the participants expended 402 kcal of additional energy by riding a bicycle with an ergometer and consumed an additional 402 kcal, either as BCAA-rich fat-free milk (high-protein diet + Exercise (HP + Ex) period) in one experiment or carbohydrates and lipids only (non–high-protein diet + Exercise (non–HP + Ex) period) in another experiment. Total 24-h urine samples were collected daily throughout the study. Fasting blood samples were collected early in the morning before and after the treatment period.
Results: Plasma valine, BCAA, and serum urea nitrogen levels were significantly elevated only after the HP + Ex period. Serum insulin-like growth factor 1 (IGF-1) levels were significantly decreased after both the non–HP + Ex and HP + Ex periods, but there was no difference in the degree of change (Δ) in serum IGF-1 level (Δ serum IGF-1) (amount of decrease in IGF-1) between the two periods. Urinary C-peptide immunoreactivity excretion levels decreased significantly during the non–HP + Ex period but were unchanged during the HP + Ex period. Serum triglyceride and remnant lipoprotein-cholesterol levels were significantly lower after both the non–HP + Ex and HP + Ex periods but did not differ between the two periods. Furthermore, there were no significant differences between the two periods in Δ serum triglyceride and Δ serum remnant lipoprotein-cholesterol (amount of decrease). Urinary noradrenaline and dopamine excretion levels were significantly higher during the HP + Ex period than during the non–HP + Ex period, and the Δ urinary noradrenaline and Δ urinary dopamine (amount of increase) were also significantly greater during the HP + Ex period than during the non–HP + Ex period.
Conclusions: A high-protein diet during exercise attenuates the insulin-sparing effects but does not affect the effects on glucose and lipid metabolism, although its effects on body protein synthesis are unclear. The combination of a high-protein diet and exercise is suggested to be an effective regimen for sarcopenic obesity.