Marine Structured Lipid Supplementation for 8 Weeks Enhances Endurance Performance and Fatty Acids Oxidation of Healthy Untrained Men during Moderate-intensity Exercise

Background Marine structured lipid is a type of functional supplement rich in omega-3 polyunsaturated fatty acids (eicosapentaenoic acid and docosahexaenoic acid) and medium-chain fatty acids. This study aimed to investigate the influence of marine structured lipid supplementation on endurance performance and substrate oxidation during moderate-intensity exercise in healthy untrained men. Methods A double-blind, placebo-controlled, randomized trial was conducted, with participants assigned to either a placebo group or a marine structured lipid group. The placebo group received daily corn oil, while the marine structured lipid group received a daily supplement containing 600 mg eicosapentaenoic acid, 260 mg docosahexaenoic acid, and 1730 mg medium-chain fatty acids for 8 weeks. Before and after supplementation, all participants were assessed for erythrocyte membrane fatty acid profile, maximal oxygen uptake, time to exhaustion, and substrate oxidation during exercise at an intensity equivalent to 65% of their pre-supplementation maximal oxygen uptake. Results After supplementation, erythrocyte eicosapentaenoic acid and docosahexaenoic acid percentages in the marine structured lipid group increased significantly and were notably higher than in the placebo group. Time to exhaustion in the marine structured lipid group also increased significantly and was longer than in the placebo group. During exercise, total fatty acid oxidation, mean fatty acid oxidation rate, and fatty acid oxidation percentage increased significantly in the marine structured lipid group compared to the placebo group, while mean carbohydrate oxidation was significantly lower. Total energy expenditure increased, and mean respiratory exchange rate decreased significantly in the marine structured lipid group. Conclusion An 8-week supplementation with marine structured lipid rich in eicosapentaenoic acid, docosahexaenoic acid, and medium-chain fatty acids extended moderate-intensity exercise duration. The potential mechanism may involve improved erythrocyte membrane fatty acid profile, enhanced fat oxidation, and reduced carbohydrate utilization, thereby improving endurance performance.