Impact of Intensive High-Fat Ingestion in the Early Stage of Recovery from Exercise Training on Substrate Metabolism during Exercise in Humans

Abstract

354Muscle glycogen depletion and/or hypoglycemia during exercise are closely associated with fatigue, and so increasing body carbohydrate (CHO) stores before exercise and/or suppressing CHO oxidation during exercise are both essential for improving endurance performance (1,2).Recently, a simple and/or practical method of ingesting an adequate amount of CHO for a few days before competition has been recommended to effectively increase body CHO stores, in contrast to the classic 1-wk glycogen-loading regimen accompanied by exhausting exercise and/or ingestion of an extremely low-CHO diet for depleting body CHO stores (3). On the other hand, it has been demonstrated that ingestion of a high-fat, low-CHO diet throughout the recovery period after exercise training (ET) increased muscle triglyceride (TG) stores, thereby enhancing whole body lipolysis and/or fat oxidation during exercise, compared with an isoenergetic high-CHO, low-fat diet (4). In general, before a competition, endurance athletes gradually change ET at high intensity to ET at moderate intensity, at which a large amount of muscle TG is utilized as an important energy source (5, 6); therefore, ingestion of not only CHO but also fat until the day before exercise would be important to elicit a CHO-sparing effect during exercise by maintaining a higher muscle TG level.TG uptake from the circulation to various tissues is highly related to lipoprotein lipase (LPL), which hydrolyzes TG in circulating chylomicrons and/or very low density lipoproteins, making free fatty acid (FFA) available for uptake by various tissues (7). It has been reported that ET increased muscle LPL activity (8,9), and that insulin increased adipose tissue LPL activity (10), whereas it decreased muscle LPL activity (11), suggesting that elevating blood TG concentration with little effect of insulin after ET is effective for accelerating TG uptake into muscles. Since muscle glycogen stores were effi ciently replenished if CHO was ingested as soon as possible after ET (12), CHO ingestion has been considered to be the fi rst priority in the early stage of recovery from ET. On the other hand, experimentally, blood TG concentration reached a peak around 4 h after ingestion of a high-fat diet (13), and blood insulin concentration reached a peak within 1 h after ingestion of a CHO-containing diet and then returned to the baseline about 4 h later (12). Although the negative effect of insulin on muscle LPL activity cannot be completely excluded, ingestion of a CHO-containing diet supplemented with high fat in the early stage of recovery from ET would not only replenish body CHO stores but also effectively increase muscle TG stores by making use of the time lag between blood insulin and TG responses. It was reported that ingestion of a high-fat, low-CHO diet for several days increased not only fat oxidation, but also heart rate (HR), rating of perceived exertion (RPE), and sympathetic activation during exercise, compared Summary Not only increasing body carbohydrate (CHO) stores before exercise b...