The Japan Institute of Sports Sciences (JISS) is the central body promoting medical and scientific support for Japanese national teams. As a sports dietitian, I have been in charge of nutritional support for the badminton national team since 2013, with the goal of improving their year-round physical condition within the framework of the JISS.

The players must participate in competitions around the world and throughout the year. They are required to obtain nutritional knowledge and the ability to choose performance foods, as they need to maintain their conditioning irrespective of time and place. Therefore, to help players improve their conditioning effectively throughout the year, we investigated problems related to performance nutrition among elite Japanese badminton athletes. We first administered surveys to clarify the existence of any nutritional problems among the players. Next, based on the results of the surveys, we established individualized recommendations for nutrient targets and provided nutritional education to solve the identified problems. The number of items in the surveys has increased annually to a present total of 8 items.

Sports dietitians involved in the field need to investigate and verify dietary problems using objective data to contribute to the international competitiveness of athletes and teams. The present data also shows that sports dietitians need to establish evidence systematically to solve problems, as evidence from the perspective of nutritional support for elite Japanese athletes and teams remains very limited.

Therefore, I will share my views on research and the support of elite athletes by introducing the nutritional support that is being provided to the Japanese national badminton team.

This review focuses on the utilization of chrono-nutrition to improve sports performance. First, we introduce the topic of circadian rhythms, which regulate several physiological functions such as body temperature, blood pressure, sleep/wake cycle, and digestion/absorption/metabolism function. In addition, we introduce methods, such as questionnaires and biological sampling, for the evaluation of circadian rhythms in humans. Second, based on our previous reports, we will discuss postprandial metabolism, focusing on the timing of diet and functional food/beverage intake. Recently, circadian rhythms have been shown to be correlated with sports performances, suggesting an interaction between circadian rhythm and exercise/sports performance (chrono-exercise). Thus, several studies have focused on the relationship between circadian rhythms and physiological functions, including sports performance, and evidence of the effects of the timing of acute exercise and exercise training on exercise performance is now accumulating. Here, we also introduce evidence of a relationship between chronotype and sports performance as well as time-of-day variations in sports performance. Finally, we refer to how circadian rhythms and chrono-nutrition can be utilized to optimize sports performance.

　A high-carbohydrate, low-fat diet (55-60% energy from carbohydrates and 25-30% energy from fats) has been recommended as an effective dietary strategy to improve athletic performance. However, recent case reports have shown that some elite athletes consume extremely high levels of carbohydrates or fats exceeding the recommended ranges. This review summarizes our recent findings regarding the effects of 1) extremely high-fat, low-carbohydrate diets (ketogenic diets), 2) extremely high-carbohydrate, low-fat diets, 3) moderate-fat diets, and 4) a ketogenic diet containing functional lipids on endurance training-induced metabolic adaptations in skeletal muscle.

【Aim】

During hospitalization, injured athletes are frequently exposed to energy restrictions as well as physical inactivity, which may induce substantial muscle atrophy. To obtain preliminary data on muscle atrophy induced by energy restriction and its combination with physical inactivity during hospitalization, we evaluated the skeletal muscle weights in rats subjected to energy restriction with/without denervation-induced physical inactivity.

【Methods】

Twenty-week-old male Fischer rats were divided into the following 3 groups: fed ad libitum (Con); subjected to 33% energy restriction (ER); or unilateral denervation in combination with the 33% energy restriction (Den-ER). After a 2-week intervention, the slow-twitch soleus and fast-twitch plantaris muscles were dissected and the muscle weights were measured.

【Results】

The soleus and plantaris muscle weights in the Den-ER group were 40% and 48% lower than those in the Con group, respectively. While no significant difference in the soleus muscle weight was observed between the ER and Con groups, the plantaris muscle weight was 7% lower in the ER group than in the Con group.

【Conclusion】

Our results suggest that simultaneous physical inactivity and energy restriction, such as during hospitalization, can induce substantial atrophy in both slow- and fast-twitch muscles. They also suggest that energy restriction alone might exert atrophic effects only in fast-twitch muscle, accounting for 15% of the muscle atrophy during hospitalization.

【Aim】

This study aimed to investigate the association of body composition and nutrient intake with physical fitness test performance of female lacrosse players for establishing strategies to improve their athletic performance.

【Methods】

We assessed the body composition (bioelectrical impedance method), endurance (Yo-Yo Test), agility (10 m × 5 shuttle run), and instantaneous power (vertical jump) of 18 adult female lacrosse club A-team players. We also measured their nutrient and energy intake required for one day of team training and two days of individual athletic training by recording their weight and photographs recording.

【Results】

Median weight and body fat values were 56.7 kg and 22.4%, respectively. Body fat percentage positively correlated with the shuttle run (r = 0.56, p = 0.01) and negatively correlated with the vertical jump (r = −0.56, p = 0.02) records. Median values for energy, protein, and carbohydrate intakes were 2,072 kcal, 72.5 g (1.3 g/kg body weight/day), and 300.3 g (5.2 g/kg body weight/day), respectively. The carbohydrate-energy ratio on the day of individual training positively correlated with the Yo-Yo Test record (r = 0.50, p = 0.03) and negatively correlated with the shuttle run record (r = −0.67, p < 0.01).

【Conclusion】

An association between body fat percentage, carbohydrate-energy ratio, and physical fitness was observed among the female lacrosse players. However, longitudinal and intervention studies are warranted in the future to assess the causal relationships between these variables.

【Aim】

Increasing lean body mass during youth is important to prevent sarcopenia and locomotive syndrome in the future. This study investigated the effects of the supplementary intake of milk protein in combination with resistance exercise training on lean body mass in female university students.

【Methods】

Thirty female university students were recruited and asked to perform bodyweight-based and resistance band-based resistance exercises 4 days a week for 12 weeks. During the training period, the subjects were instructed to consume cookies containing either 10 g of milk protein (MP: n=15) or isoenergetic carbohydrate (CON: n=15) daily. Body composition and muscle thickness were measured before and after the interventions.

【Results】

Twenty-one subjects (CON: n=9; MP: n=12) successfully completed the 12-week nutritional and training interventions. Lean body mass, lower-limb muscle mass, and quadriceps muscle thickness were significantly increased with training in the MP group, but not in the CON group, with the increases in the MP group being greater than those in the CON group.

【Conclusion】

Our results may suggest that the supplementary intake of milk protein during resistance exercise training may be an effective nutritional strategy to increase lean body mass in young women.

【Aim】

The purpose of this study was to clarify a relationship among dietary surveys, blood parameters including vitamin B₁, C levels, and indefinite complaints, as a nutritional assessment for understanding vitamin nutritional status in athletes.

【Methods】

Seven female collegiate basketball players (group A) and 14 female college students (group NA) participated in this study. A survey was conducted on nutritional status over 3 days, blood tests (including vitamin B₁, C levels) were performed, and a questionnaire was conducted on lifestyle, indefinite complaints, and eating habits. The relationships among these items were examined, featuring parameters associated with vitamin B₁ and C.

【Results】

There was a significant positive correlation between vitamin B₁ intake (mg/1,000 kcal/day) and blood levels in group A, but not in group NA. There was no significant correlation between blood vitamin C levels and vitamin C intake in either group. No relationship between the number of indefinite complaints and dietary survey results, and blood levels was found in either group, however, some indefinite complaints that were more frequent in group A than in group NA were considered to be related to energy intake and blood levels.

【Conclusion】

The results of this study suggest that evaluation of vitamin B₁ nutritional status in athletes needs to assess not only dietary intake but also blood levels or indefinite complaints peculiar to athletes. Further investigation about vitamin C assessment methods needs to be performed.