ABSTRACT
Butyrate is a short-chain fatty acid produced during fermentation of fibers and other substrates in the gastrointestinal tract. A recent study has shown that elevation of butyrate availability by dietary supplementation exerts favorable effects on glucose metabolism. However, it remains unclear whether butyrate intake affects insulin-sensitive glucose transporter (GLUT-4) protein content in skeletal muscle, which has been shown to be closely related to muscle glucose transport capacity and whole-body insulin sensitivity. The purpose of this study was therefore to examine the effects of dietary intake of butyrate on muscle GLUT-4 protein content and whole-body insulin sensitivity in rats. Seven-week-old male Sprague-Dawley rats were placed on a sodium butyrate diet (SB) or standard chow diet (CON) for 2 wks. Sodium butyrate was incorporated into the standard chow diet at 5 % wt/wt. After the 2-wk dietary intervention, insulin tolerance test (ITT) was performed to evaluate whole-body insulin sensitivity. GLUT-4 protein contents in soleus and epitrochlearis muscles were determined by western blot analysis. There were no significant differences in body weight, food intake and intra-abdominal fat weight between the SB and CON groups. GLUT-4 protein contents in soleus and epitrochlearis muscle were significantly lower in the SB than CON group. The SB group had less reduction in glycemia than did the CON group during ITT. These results suggest that dietary intake of sodium butyrate may decrease muscle GLUT-4 protein content and impair whole-body insulin sensitivity in rats.
ABSTRACT
The purpose of this study was to examine the effect of fructose ingestion on maximal exercise performance capacity following prolonged steady-state exercise compared with glucose or placebo ingestion, in 7 male college students (age 23.3±0.7 yr, height 171.3±1.9 cm, weight 68.4±1.4 kg, Vo2max 3.5±0.2 L/min, mean ± SEM) . The subjects cycled constantly on an ergometer at 59± 2 % Vo2max for 100 min divided in the middle by a 5-min rest, and then performed 10 min of all-out self-paced cycling. They ingested either 8 % fructose solution (F), 8 % glucose solution (G) or artifi-cially sweetened placebo (P) before and during exercise (at 20, 40, 65, 85 mm) . Before exercise and at 50 and 100 min of exercise and 5 min after the performance ride, blood samples were collected for determination of the concentrations of blood lactate, serum glucose and serum FFA. In the G trial, the serum FFA level was significantly lower than in the P and F trials at any of the time points dur-ing and after exercise (vs. P ; p<0.01, vs. F ; p<0.05) . However, glucose ingestion maintained serum glucose at a significantly higher level during and after exercise than placebo ingestion (p< 0.01) and improved the total work output in the 10-min performance ride (G vs. P ; 135± 8 KJ vs. 128± 8 KJ, p<0.05) . Although in the F trial, the serum FFA level was elevated during exercise compared to that in the G trial and the serum glucose level was significantly higher than in the P trial (vs. P ; p<0.01), the blood lactate level after exercise was lower than in the G trial and total work output was similar to that in the P trial (123± 8 KJ, vs. G ; p<0.01) . These results indicate that fructose ingestion before and during exercise cannot improve the ability to perform high-intensity exercise late in prolonged exercise despite maintaining the serum glucose level.