The effects of a high carbohydrate diet on postprandial energy expenditure during exercise in rats

Effects of dietary composition and exercise timing on substrate utilization and sympathoadrenal function in healthy young women

The effects of dietary composition (high-fat [FAT] or high-carbohydrate [CHO]) and exercise timing (preprandial exercise [Ex-] or postprandial exercise [-Ex]) on postprandial substrate utilization and sympathoadrenal function were studied in seven women aged 20 to 21 years. The experimental protocol included four different sessions (Ex-FAT, FAT-Ex, Ex-CHO, and CHO-Ex). The FAT and CHO diets provided 48% and 5% fat, respectively. On the experimental days, subjects ate a meal containing the same caloric energy at lunchtime, and they exercised for 30 minutes on a bicycle ergometer at an intensity of 60% maximal oxygen consumption (VO2max) before and after the meal, followed by rest for 3 hours. The resting respiratory quotient (RQ) was significantly lower (P < .05) with the FAT diet or postprandial exercise. The mean RQ during the experimental period was 0.78, 0.75, 0.81, and 0.77 in Ex-FAT, FAT-Ex, Ex-CHO, and CHO-Ex groups, respectively. The total area under the curve of serum norepinephrine (NE) as an index of NE secretion was significantly higher (P < .05) with the FAT diet or postprandial exercise (130.2, 175.8, 33.0, and 136.9 ng x mL(-1) x min, respectively). A negative correlation was observed between the RQ and the total area of NE (r = .49, P < .05). The serum thyroid hormone level was not influenced by dietary composition and exercise timing. These results suggest that postprandial exercise, especially after intake of a FAT diet, increases fat utilization via a slightly larger decrease in the RQ. This might be related to the sympathoadrenal system at rest and during exercise.

Effects of short-term dietary change from high fat to high carbohydrate diets on the storage and utilization of glycogen and triacylglycerol in untrained rats

The effects of short-term diet change from high fat (F) to high carbohydrate (C) (or vice versa) on the storage and utilization of glycogen and triacylglycerol (TG) in muscle and liver were studied in untrained rats. Rats were fed on an F or C diet for 28 days. For an additional 3 days, half of the rats in both F and C groups were fed the same diets as before (F-F and C-C) and the other half of the rats were switched to the counterpart diets (F-C and C-F). On the final day of the experiment, half of the rats in each diet group were exercised by swimming for 1.5 h and the other half were rested. Short-term diet change from F to C diets increased, but the change from C to F diets decreased, glycogen stores of soleus and plantaris muscles and liver, resulting in no difference in glycogen stores between F-C and C-C, and between F-F and C-F. The dietary change also had an affect on TG stores of red gastrocnemius muscle and liver-however, muscle TG stores were still higher in F-C than in C-C and C-F, and there were no differences in liver TG stores between F-C and C-F. Exercise decreased muscle glycogen contents markedly in F-C and C-C, whereas, it decreased muscle TG concentrations in F-F and C-F. Liver glycogen depletion was lower in F-C than in other groups. Lipolytic activities of epididymal adipose tissue at rest and postexercise were no differences between F-F and F-C, and were higher in F-C than in C-C and C-F. beta-adrenergic receptor binding was determined with [125I] iodocyanopindolol, and maximal numbers of beta-adrenergic receptor of plasma membrane from perirenal adipose tissue were approximately 170%-200% higher in F-C than in other groups at rest and postexercise. These results suggested that short-term C diet fed rats adapted to F diet enhanced not only glycogen stores of muscle and liver but also did not decrease lipolytic activity of adipose tissue with increased beta-adrenergic receptor density, resulting in the preservation of energy reserves (glycogen and TG) of muscle at rest, and liver glycogen sparing during exercise.

Sympathetic activity is lower in rats fed a beef tallow diet than in rats fed a safflower oil diet

Effects of dietary fats consisting of different fatty acids on sympathetic activity and body fat accumulation were studied in rats. Rats were meal-fed an isoenergetic diet based on either beef tallow or safflower oil for 8 weeks. Carcass fat content was greater (P < .05) in rats fed the beef tallow diet than in rats fed the safflower oil diet. Norepinephrine (NE) turnover rate was significantly lower (P < .05) in interscapular brown adipose tissue (IBAT) and pancreas in rats fed the beef tallow diet than in rats fed the safflower oil diet, resulting in a decreased (P < .05) diet-induced thermogenesis (DIT) and an increased (P < .05) serum insulin concentration in the former. To confirm the effects of dietary fats on sympathetic activity in relation to body fat accumulation, rats were chemically sympathectomized. Sympathectomy abolished the differences in body fat accumulation, DIT, and serum insulin concentration between the two dietary groups. These results suggest that the beef tallow diet promotes body fat accumulation by reducing sympathetic activity as compared with intake of the safflower oil diet.