It is widely known that nutrition is important for athletes not only to determine the outcome of competition, but also to increase their physical fitness during training periods. Among energy-producing nutrients, carbohydrates have been studied for a long time as a source of energy during exercise. For example, research is conducted on topics such as the timing of carbohydrate intake prior to competition, the carbohydrate intake required for recovery after competition, and the relationship between the carbohydrate type/concentration and the absorption rate. Additionally, since protein is a material for skeletal muscle, a large amount of evidence has been accumulated from the viewpoint of bodybuilding. For these nutrients, the recommended amount to be taken is shown depending on the duration of training and the intensity of exercise.
Conversely, although lipids are one of the important nutrients, they are often viewed by athletes as villains that cause higher levels of body fat. Furthermore, when compared to carbohydrates and proteins, there is limited research in the field of sports nutrition on lipid intake. Even in sports nutrition textbooks published in Japan and overseas, there is extremely limited information regarding lipid intake. However, in recent years, there has been more research focusing on the physiological function and fatty acid composition possessed by lipids, and new developments are taking place in lipid research as part of sports nutrition.
The first example is the function in which lipids promote the secretion of insulin. Rapid recovery of decreased muscle glycogen is essential for competitions where multiple matches are played in a single day. Thus far, when examining the recovery of muscle glycogen after exercise, a large number of research results have been accumulated regarding carbohydrates in terms of type, concentration, and intake timing, but there has been no research focusing on lipids. However, a recently published research report indicated increased insulin secretion when beverages containing lipids (milk was used in this study) are ingested together with carbohydrates, which are the source of glycogen (Maruyama et al., Japanese Journal of Sports Medicine, 2018). In this way, the possibility of using lipids as a tool to promote muscle glycogen recovery has been indicated.
Results related to the maintenance of lean body mass (skeletal muscle mass) have also been reported in research with athletes. Medium-chain fatty acids with short fatty acid chains are known for being easily used as energy. A study of college wrestlers showed that the group receiving medium-chain fatty acids had less of a decrease in skeletal muscle mass compared to the group receiving long-chain fatty acids (Nosaka et al., Journal of Japanese Society of Clinical Nutrition, 2011). This research shows the possibility that lipid intake may not result in higher body fat; instead, depending on the characteristics of the fatty acid ingested, it may be effective in maintaining skeletal muscle mass.
In this way, in addition to an understanding of lipids as an energy source, knowledge on lipids as part of diet is also increasing even in fields in which the relationship with lipid intake had not been investigated thus far, such as recovery of muscle glycogen and maintenance of skeletal muscle mass. As such, further growth in lipid research is expected in the future.