Abstract
e compared the 24 h changes in interstitial uid glucose concentration (IGC) following a simulated soccer match between subjects consuming a high-carbohydrate (HCHO; 8 g/kg BW/day) diet and those consuming a moderate-carbohydrate (MCHO; 4 g/kg BW/day) diet. Eight active healthy males participated in two different trials. The subjects were provided with the prescribed diets from days 1 to 3. On day 3, the subjects performed 90 min (2 bouts 45 min) of exercise simulating a soccer match. The IGC of the upper arm was continuously monitored from days 1 to 4. No signi cant difference in the IGC was observed between trials during exercise. The total area under the curve (t-AUC) value during exercise did not signi cantly differ between the HCHO (9719 305 mg/dL 90 min) and MCHO (9991 140 mg/dL 90 min). Serum total ketone body and beta-hydroxybutyrate concentrations were signi cantly higher in the MCHO than in the HCHO after a second bout of exercise. No signi cant differences in the IGC were observed between trials at any time point during the night after exercise (0:007:00). In addition, t-AUC value during the night did not signi cantly differ between the HCHO (32,378 873 mg/dL 420 min) and MCHO (31,749 633 mg/dL 420 min). In conclusion, two days of consuming different carbohydrate
second bout of exercise. No signi cant differences in the IGC were observed between trials at any time point during the night after exercise (0:007:00). In addition, t-AUC value during the night did not signi cantly differ between the HCHO (32,378 873 mg/dL 420 min) and MCHO (31,749 633 mg/dL 420 min). In conclusion, two days of consuming different carbohydrate intake levels did not signi cantly affect the IGC during a 90 min simulated soccer match. Moreover, the IGC during the night following the exercise did not signi cantly differ between the two trials despite the different carbohydrate intake levels (8 vs. 4 g/kg BW/day). Keywords:continuous glucose monitoring; glucose; carbohydrate; football 1. Introduction Carbohydrate (CHO) is a major source of energy during prolonged exercise in athletes, and it is recommended to increase CHO intake above the normal level during the few days before competing [1]. Sympathetic nervous system activity and hepatic glycogenolysis are stimulated during moderate or high-intensity exercise. Thus, blood glucose concentrations are maintained during exercise unless hepatic glycogen stores become markedly low [2]. Endurance athletes have a strong capacity to maintain their blood glucose concentrations during prolonged exercise compared to untrained subjects [3]. Moreover, 40% of endurance athletes present with glucose concentrations above the reference range for more than 70% of the time, except 2 h after a meal [4]. Therefore, it appears that blood glucose level is maintained, even when CHO intake is less than the recommended amount among athletes. The main nutritional factors that induce fatigue during a team sports game (e.g., soccer, rugby, basketball) are depletion of muscle glycogen and hypoglycemia [5]. Insuf cient CHO intake by soccer players before a match leads to depleted muscle glycogen, resulting in decreased endurance capacity [6] and decreased sprinting speed during the second half [7]. It has also been reported that consuming additional CHO before and during exercise contributes to maintaining a higher level of blood glucose, which prevents a drop in Nutrients2023,15, 4746.
sprinting speed during the second half [7]. It has also been reported that consuming additional CHO before and during exercise contributes to maintaining a higher level of blood glucose, which prevents a drop in Nutrients2023,15, 4746.
Nutrients2023,15, 4746 2 of 12 performance and cognitive skills [8,9]. Therefore, 68 g/kg BW CHO intake per 24 h during congested xture schedules is recommended for soccer players [10]. Moreover, additional CHO is recommended before and during a game [11,12], despite the relative rarity of hypoglycemia during a soccer match [13]. Professional soccer players in England consume only about 4 g/kg BW/day on training days during the in-season period, including the day before a match [14]. As exercise-induced physiological stress causes gastrointestinal disturbance and reduces food intake [15], consuming the recommended amount of CHO during a busy match schedule may not be practical for some athletes. Several studies [7,1618] have reported changes in muscle glycogen before and after a soccer match, whereas continuous changes in blood glucose during exercise and the recovery period (until the next morning) under insuf cient CHO intake remain unclear. In the present study, we compared the 24 h changes in IGC following a simulated soccer match between trials that consumed a high-CHO diet and those that had a moderate-CHO diet. We hypothesized that IGC would not be different during and after exercise (including the night) between the trials. 2. Methods 2.1. Subjects Eight males (mean standard error, age: 23.9 1.1 years, height: 170.1 2.3 cm, body weight: 63.3 2.9 kg, body mass index: 21.9 0.8 kg/m 2 ) participated in the present study. All subjects were physically active with recreational resistance exercise or endurance exercise, but none of them were involved in regular resistance or endurance training within 6 months prior to the study. All subjects were informed of the purpose of the study, the experimental procedures, and the possible risks involved in the study, and written informed consent was obtained. The study was approved by the Ethical Committee for Human Experiments at Ritsumeikan University following the Declaration of Helsinki. 2.2. Experimental Overview A cross-over design approach was adopted (Figure). The main experiment involved two trials consisting of a high-carbohydrate (HCHO; 8 g/kg BW/day CHO) trial and an energy-matched moderate-carbohydrate (MCHO; 4 g/kg BW/day CHO) trial. Subjects initially visited the laboratory for preliminary measurements of
by the Ethical Committee for Human Experiments at Ritsumeikan University following the Declaration of Helsinki. 2.2. Experimental Overview A cross-over design approach was adopted (Figure). The main experiment involved two trials consisting of a high-carbohydrate (HCHO; 8 g/kg BW/day CHO) trial and an energy-matched moderate-carbohydrate (MCHO; 4 g/kg BW/day CHO) trial. Subjects initially visited the laboratory for preliminary measurements of height and body weight (BW) using a height and weight meter (WB-510, Tania Inc., Tokyo, Japan). The BW at this time point was utilized for the dietary prescription. A dietary survey was conducted using the food frequency questionnaire (FFQ) before the experiment started to evaluate typical energy and nutrient intake. FFQs are frequently used to assess diet in epidemiological studies and normally include queries on the intake of more than 100 food and beverage items [19]. A FFQ is useful for assessing dietary intake among Japanese [20]. The dietary analysis was conducted using specially designed software (Excel Eiyo-kun version 9.0, Kenpaku-sha, Tokyo, Japan).Nutrients 2023, 15, x FOR PEER REVIEW 2 of 12 second half [7]. It has also been reported that consuming additional CHO before and dur- ing exercise contributes to maintaining a higher level of blood glucose, which prevents a drop in performance and cognitive skills [8,9]. Therefore, 6–8 g/kg BW CHO intake per 24 h during congested fixture schedules is recommended for soccer players [10]. Moreover, additional CHO is recommended before and during a game [11,12], despite the relative rarity of hypoglycemia during a soccer match [13]. Professional soccer players in England consume only about 4 g/kg BW/day on training days during the in-season period, includ- ing the day before a match [14]. As exercise-induced physiological stress causes gastroin- testinal disturbance and reduces food intake [15], consuming the recommended amount of CHO during a busy match schedule may not be practical for some athletes. Several studies [7,16–18] have reported changes in muscle glycogen before and after a soccer match, whereas continuous changes in blood glucose during exercise and the re- covery period (until the next morning) under insufficient CHO intake remain unclear. In the present study, we compared
recommended amount of CHO during a busy match schedule may not be practical for some athletes. Several studies [7,16–18] have reported changes in muscle glycogen before and after a soccer match, whereas continuous changes in blood glucose during exercise and the re- covery period (until the next morning) under insufficient CHO intake remain unclear. In the present study, we compared the 24 h changes in IGC following a simulated soccer match between trials that consumed a high-CHO diet and those that had a moderate-CHO diet. We hypothesized that IGC would not be different during and after exercise (includ- ing the night) between the trials. 2. Methods 2.1. Subjects Eight males (mean ± standard error, age: 23.9 ± 1.1 years, height: 170.1 ± 2.3 cm, body weight: 63.3 ± 2.9 kg, body mass index: 21.9 ± 0.8 kg/m 2 ) participated in the present study. All subjects were physically active with recreational resistance exercise or endurance ex- ercise, but none of them were involved in regular resistance or endurance training within 6 months prior to the study. All subjects were informed of the purpose of the study, the experimental procedures, and the possible risks involved in the study, and written in- formed consent was obtained. The study was approved by the Ethical Committee for Hu- man Experiments at Ritsumeikan University following the Declaration of Helsinki. 2.2. Experimental Overview A cross-over design approach was adopted (Figure 1). The main experiment involved two trials consisting of a high-carbohydrate (HCHO; 8 g/kg BW/day CHO) trial and an energy-matched moderate-carbohydrate (MCHO; 4 g/kg BW/day CHO) trial. Subjects in- itially visited the laboratory for preliminary measurements of height and body weight (BW) using a height and weight meter (WB-510, Tania Inc., Tokyo, Japan). The BW at this time point was utilized for the dietary prescription. A dietary survey was conducted using the food frequency questionnaire (FFQ) before the experiment started to evaluate typical energy and nutrient intake. FFQs are frequently used to assess diet in epidemiological studies and normally include queries on the intake of more than 100 food and beverage items [19]. A FFQ is
this time point was utilized for the dietary prescription. A dietary survey was conducted using the food frequency questionnaire (FFQ) before the experiment started to evaluate typical energy and nutrient intake. FFQs are frequently used to assess diet in epidemiological studies and normally include queries on the intake of more than 100 food and beverage items [19]. A FFQ is useful for assessing dietary intake among Japanese [20]. The dietary analysis was conducted using specially designed software (Excel Eiyo-kun version 9.0, Kenpaku-sha, Tokyo, Japan). Figure 1. Study protocol. IGC: Interstitial fluid glucose concentration. BW: Body weight. HCHO: High-carbohydrate diet. MCHO: Moderate-carbohydrate diet. Figure 1. Study protocol. IGC: Interstitial uid glucose concentration. BW: Body weight. HCHO: High-carbohydrate diet. MCHO: Moderate-carbohydrate diet. Each trial consisted of 4 consecutive days (days 14), separated by a 10-day washout period between trials. Subjects were provided a prescribed diet from days 1 to 3 (until
Nutrients2023,15, 4746 3 of 12 dinner on the exercise day). IGC was continuously monitored from days 1 to 4 (until 9:00 a.m.). Subjects maintained their typical physical activity levels on days 1 and 2. On day 3, they performed 90 min (2 bouts 45 min) of running exercise on a treadmill to simulate a soccer match. Blood samples were collected three times, before exercise and immediately after completing the rst and second bouts of exercise. Acetone levels in exhaled breath were evaluated ve times before exercise, after completing the rst and second bouts, 30 min after completing the exercise, and the day after exercise (before breakfast). 2.3. Dietary Intervention (Days 13) In total, nine prescribed meals were provided from days 1 to 3 and subjects consumed only the prescribed diet at the designated time in each trial. Subjects in the HCHO had the prescribed CHO-rich snacks at 4:00 p.m. on days 1 to 3. In addition, the subjects were allowed to drink waterad libitum. The diets were provided as prepackaged food (Nissin Healthcare Food Service Co., Ltd., Tokyo, Japan, and Nosh Co., Ltd., Osaka, Japan) and prepared foods were purchased at a supermarket. Total energy intake was deter- mined by referring to the energy requirement for males (1829 years old) and physical activity level II in the dietary reference intake for Japanese (ver. 2020). The HCHO diet contained 8 g/kg BW/day CHO, determined based on the recommendation of the Union of European Football Associations (UEFA) expert group [10]. The MCHO diet contained 4 g/kg BW/day CHO, equivalent to the CHO intake of elite football players [14]. Table shows the structure and provision of the diets, ensuring total energy intake and the per- centage of macronutrients. The macronutrient contents were calculated using dedicated software (Excel Eiyo-kun version 9.0, Kenpaku-sha) and food labels. On the day of the exercise (day 3), the subjects consumed breakfast containing 2.4 g/kg BW CHO (HCHO) or 1.4 g/kg BW CHO (MCHO) 90 min before starting the exercise, respectively. Subjects had breakfast, lunch, and snacks at the dining space attached to the laboratory and all their meals
using dedicated software (Excel Eiyo-kun version 9.0, Kenpaku-sha) and food labels. On the day of the exercise (day 3), the subjects consumed breakfast containing 2.4 g/kg BW CHO (HCHO) or 1.4 g/kg BW CHO (MCHO) 90 min before starting the exercise, respectively. Subjects had breakfast, lunch, and snacks at the dining space attached to the laboratory and all their meals were consumed. Dinner was taken home and subjects reported how much they consumed. Subjects consumed all of the food provided for both trials. Table 1.Total energy intake and macronutrients during the intervention period. Variables HCHO MCHO Day 1 Day 2 Day 3 Average Day 1 Day 2 Day 3 Average Energy (kcal) 2626 118 2616 128 2637 114 2627 120 2625 119 2628 123 2621 121 2625 120 CHO (g) 504.4 22.1 * 503.7 25.6 * 508.0 22.2 * 505.3 23.2 * 252.8 12.0 254.8 11.7 253.3 11.3 253.8 11.8 (g/kg) 7.9 0.04 * 7.9 0.06 * 8.0 0.03 * 8.0 0.04 * 4.0 0.03 4.0 0.04 4.0 0.03 4.0 0.04 (for energy) 76% * 77% * 77% * 77% * 39% 39% 39% 39% Protein (g) 90.1 4.2 * 88.9 4.2 * 89.6 3.7 * 89.7 4.0 * 94.3 4.2 95.5 4.6 95.2 4.3 95.0 4.3 (g/kg) 1.4 0.02 1.4 0.02 * 1.4 0.00 * 1.4 0.01 * 1.5 0.02 1.5 0.01 1.5 0.01 1.5 0.00 (for energy) 14% 13% * 13% 13% 14% 14% 14% 14% Fat (g) 28.2 1.4 * 27.8 1.1 * 28.1 1.2 * 28.1 1.2 * 137.9 6.0 137.2 6.4 136.5 6.5 137.4 6.2 (g/kg) 0.4 0.00 * 0.4 0.01 * 0.4 0.01 * 0.4 0.02 * 2.2 0.02 2.1 0.01 2.1 0.01 2.2 0.02 (for energy) 10% * 10% * 10% * 10% * 47% 47% 47% 47% Values are means SE. CHO: Carbohydrate. HCHO: High carbohydrate diet. MCHO: Moderate carbohydrate diet. *:p< 0.05 vs. MCHO. 2.4. Exercise Protocol (Day 3) The subjects conducted a 90 min running exercise simulating a soccer match on a treadmill (Elevation series E95Ta; Life Fitness Corp., Tokyo, Japan; Valiant; Lode, Groningen, the Netherlands). All subjects used the
* 47% 47% 47% 47% Values are means SE. CHO: Carbohydrate. HCHO: High carbohydrate diet. MCHO: Moderate carbohydrate diet. *:p< 0.05 vs. MCHO. 2.4. Exercise Protocol (Day 3) The subjects conducted a 90 min running exercise simulating a soccer match on a treadmill (Elevation series E95Ta; Life Fitness Corp., Tokyo, Japan; Valiant; Lode, Groningen, the Netherlands). All subjects used the same treadmill for both trials. The exercise protocol was modi ed from one utilized in previous studies [2123]. The exercise during both trials consisted of two repeated bouts of 45 min (90 min in total) separated by 15 min of rest. Each bout was 9 5 min of exercise, including walking (4 km/h) for 90 s, jogging (8 km/h) for 90 s, running (12 km/h) for 75 s, and sprinting (18 km/h) for 45 s. The total running distance covered was 13.95 km in 90 min. The slope of the treadmill was set to 1%. Heart rate (HR) was recorded every 1 min during exercise using a wireless HR monitor (RCX5;
Nutrients2023,15, 4746 4 of 12 Polar Electro, Kempele, Finland). The rating of perceived exertion (RPE) was measured every 5 min while walking at 4 km/h. All subjects completed a 90 min running exercise in both trials. 2.5. Measurements 2.5.1. Body Composition Subjects arrived at the laboratory at 8:00 a.m. after an overnight fast. After rest, body composition was evaluated before eating breakfast on day 1, day 3 (exercise day), and day 4 (the day after the exercise). BW, fat-free mass (FFM), fat mass (FM), and total body water were measured via bio-impedance analysis using a body composition analyzer (InBody 770, In Body Japan Inc., Tokyo, Japan). 2.5.2. IGC The IGC was continuously evaluated by a continuous glucose monitoring (CGM) system (FreeStyle Libre Flash Glucose Monitoring Device, FreeStyle Libre; Abbott Diabetes Care, Alameda, CA, USA; [2426]). The subjects wore the device from day 1 (9:00 a.m.) until day 4 (9:00 a.m.). The sensor was attached to the skin on the back of the upper arm and continuously recorded the average IGC over a 15 min period [27]. Subjects scanned the sensors at intervals of at least 8 h while wearing the device. In addition, the IGC was measured by scanning every 5 min during the 90 min of exercise. A CGM system provides glucose estimates that are comparable with self-monitoring blood concentrations of glucose in normo-glycemic individuals [28]. The Japan Diabetes Society describes that the FreeStyle Libre is available as a medical device for daily self-management of diabetes. 2.5.3. Levels of Acetone in Exhaled Breath To evaluate the changes in fat metabolism associated with exercise and the different CHO intake levels, the acetone levels in exhaled breath were determined ve times during both trials before starting the exercise, immediately after the rst and second bouts, 30 min after completing the exercise, and before breakfast the next day after the exercise (8:00 a.m.). End-tidal air was collected at each measurement time using a special bag. The collected acetone was analyzed by gas chromatography (SGEA-PA-A, Nissha Co., Ltd., Kyoto, Japan). 2.5.4. Blood Sampling and Analysis Blood samples were collected from an antecubital vein
rst and second bouts, 30 min after completing the exercise, and before breakfast the next day after the exercise (8:00 a.m.). End-tidal air was collected at each measurement time using a special bag. The collected acetone was analyzed by gas chromatography (SGEA-PA-A, Nissha Co., Ltd., Kyoto, Japan). 2.5.4. Blood Sampling and Analysis Blood samples were collected from an antecubital vein three times during both trials before exercise and immediately after completing the rst and second bouts. The serum was obtained after 10 min of centrifugation (3000 rpm, 4 C) and stored at 80 C until further analysis. Blood glucose, lactate, serum insulin, myoglobin, total ketone body, and Beta-hydroxybutyric acid (BHB) concentrations were measured. Serum insulin, myoglobin, total ketone body, and BHB concentrations were measured using a clinical laboratory (SRL, Tokyo, Japan). Blood glucose and lactate concentrations were measured immediately after the blood was collected using a glucose analyzer (Freestyle, Nipro Inc., Osaka, Japan) and a lactate analyzer (Lactate Pro, Arkray, Inc., Kyoto, Japan). 2.5.5. Perceived Fatigue Participants were asked to rate their perceived fatigue using a visual analog scale (VAS) before exercise, immediately after completing the rst and second bouts, 30 min after completing the exercise, and the morning after the exercise. The VAS consisted of a 10 cm line ranging from 0 to 10, where 0 indicated no fatigue at all and 10 indicated extreme fatigue [29]. 2.5.6. Statistical Analysis Data are expressed as mean standard error. Time-course changes in the IGC, blood parameters, acetone levels in exhaled breath, and body composition were compared using two-way repeated-measures analysis of variance (ANOVA) to determine the interaction
Description
The study investigates glucose responses during exercise with varying carbohydrate intake.