Many athletes and physical activity practitioners consider fat and lipid as the performance and health deteriorating factors and have been frequently advised to consume them as little as possible. However, we have recently found that co-ingestion of fat with carbohydrate potentiated post-exercise muscle glycogen recovery and dietary intake of functional lipid ameliorated immobilization-induced muscle atrophy, suggesting that lipid intake can exert favorable effects in athletes. In this review, we describe the new nutritional strategies using lipid to enhance exercise performance.

The medium-chain triglycerides (MCTs) are composed of medium-chain fatty acids and glycerol. The MCTs are easily and quickly digested to free fatty acids in the small intestine and subsequent quickly metabolized as energy sources compared with long-chain triglycerides. This is because that the micellization with the bile is not necessary for the digestion and absorption of MCTs, the medium-chain fatty acids digested in the small intestine are not re-synthesized into triglycerides and carnitine binding to the fatty acids, a rate-controlling step of β-oxidation, is not necessary. In addition, several studies demonstrated that intake of MCTs in animals enhanced expression and/or enzyme activity of genes related to metabolism such as β-oxidation, glycolysis system, citric acid cycle, electron transport system and fatty acid synthesis. The intake of MCTs enhanced the insulin action in animal models with insulin resistance or with undernutrition. These results indicate that MCTs has functions of activating energy metabolism proactively by enhancing expression/activity of the rate-controlling enzymes as well as of an energy sources. Furthermore, recent studies have demonstrated that MCT metabolizes such as β-hydroxybutyric acid and citric acid can enhance an epigenetic memory histone acetylation. We have demonstrated that a medium-chain fatty acid caprylic acid enhanced not only expression of intestinal genes related to digestion/absorption of lipids and carbohydrates, but also that of their transcriptional factor peroxisome proliferator-activated receptor α and the histone acetyl-transferase CREB binding protein/p300. These evidences indicate that MCTs can enhance metabolism and digestion/absorption of the nutrients by enhancing expression of genes related to metabolic genes and those related to enhancing the histone acetylation.

Sarcopenia—the age-related loss of skeletal muscle mass, strength, and function —is a common clinical problem in older people, and often leads to severe adverse outcomes. The growing interest of sarcopenia has highlighted the need to understand more about its management. The preservation or improvement of physical function and independent living are vital in frail older adults, and sarcopenia is a major contributor to physical frailty. Several definitions of sarcopenia have been globally proposed thus far, although no consensus has been reached. Moreover, sarcopenia is now recognized as an independent condition by an ICD-10-CM code.

Medium chain triglyceride (MCT), a lipid of carbon chain 8-10, has high energy efficiency, and is used immediately as an energy source. MCT is considered to be one of extremely useful nutrients for the elderly with malnutrition and sarcopenia with decreased food intake. A recent study shows that oral ingestion of MCT promotes the activation of ghrelin, and, therefore, MCT has gained much attention from the point of appetite stimulation in older adults.

The absorption pathway of dietary lipophilic components is different from that of water-soluble molecules in the diet. Formation of micelles in the intestinal lumen is an important step for the absorption of hydrophobic compounds. Such molecules cannot reach the intestinal epithelia without micellar formation because of the presence of the unstirred water layer overlying the brush border. Once reached the brush border, the components are taken up into the enterocytes either via simple diffusion or protein-mediated membrane transport. Susceptibilities to be absorbed and deposited in the body depend on the extent of lipophilicity of components. In this review, the absorption process of dietary lipids, such as triglycerides and phospholipids, is briefly illustrated. Furthermore, our research on the bioavailability of dietary flavonoids, which possess relatively low lipophilicity, is also presented.