Glycogen is an important source of energy production during endurance exercise, such as marathon. Due to limited storage of glycogen in muscle and liver, augmentation of fat oxidation is known to delay depletion of muscle glycogen, leading to improvement of endurance performance. N-3 polyunsaturated fatty acids (n-3 PUFA) resulting from the form of fish has shown to enhance fat oxidation at rest. However, effect of n-3 PUFA on substrate metabolism during prolonged exercise remains unclear. The present study was designed to investigate whether dietary n-3 PUFA enhances fat oxidation during exercise and endurance performance. Thirteen healthy men were divided into n-3 PUFA group [n=6, 6g/day of fish oil; 1,800mg eicosapentaenoic acid (EPA), 2,700mg docosahexiaenoic acid (DHA)] or CON group [n=7, 6g/day of olive oil]. The subjects ingested each supplement for 4-weeks. Before and after the treatment period, a 60-min pedaling exercise at 65% of maximal oxygen uptake followed by 5 km-time-trial was conducted. Resting concentrations of serum EPA and DHA, EPA/AA were significantly elevated in the n-3 PUFA group only. After supplementation period, the n-3 PUFA group increased significantly exercise-induced elevations of serum free fatty acids and glycerol concentrations, and lowered respiratory exchange ratio during a 60-min pedaling exercise. Similar changes were not observed in the CON group. However, treatment with n-3 PUFA did not affect significantly result of 5km-time-trial. Four-week supplementation of n-3 PUFA increased exercise-induced lipolysis and fat oxidation during prolonged exercise. However, the augmented fat metabolism did not affect endurance performance.

Background & Objectives: Generally, food intake of athletes decrease under hot summer and, therefore, it would affect on their physiques and the athletic power (competition). The present study investigated the effect of decreased energy intake on athletes’ physique, energy expenditure and/or thyroid hormones. Methods: Forty two males of high school baseball team in Hokuriku area, Japan, participated in this study. The nutrition survey and physical measurements were performed, and total energy expenditure (TEE) from activity records were estimated in April, July, and December. Energy balance was determined from energy intake and TEE. Furthermore, the resting energy metabolism (REE) was measured by the expired gas analysis. Thyroid hormones were assayed respectively T3, FT3, and FT4. Results: Seventy percent of baseball players showed reduction of energy intake in summer. We, accurately, recognized that one can see two groups, i,e., a group that energy intake was decreased in summer (LA) and another was not decreased in the same summer (HA). Many subjects showed decrease of energy intake but their TEE was rather increased in summer. The energy balance of LA group was largely negative, but that of HA group was slightly negative. In LA group, body weight, BMI, and MAC (midarm circumference) were significantly decreased by 2∼4% in summer than that in spring, while the decrease of physical measurements is 1∼2% in HA group. Thus, a large negative energy balance affected the physique negatively. From energy composition of diet, it seems that LA group had high carbohydrate energy diet and HA group had high fat diet. There was a significant positive correlation between the energy intake and each of the nutrient intakes. The REE was significantly decreased in summer and thus it seems to be related with energy intake. FT3 and T3 were not changed in summer but were in winter, and it looks to be slightly related with REE. Conclusion: Decrease of energy intake in summer indicated a large negative effect on physique such as body weight, MAC. The decrease of energy intake in summer seems to be related with reduction of REE.