Study design Ratings of subjective feelings of hunger, energy intake (EI), acylated ghrelin, leptin, insulin and glucose levels in response to rest and exercise were investigated using a randomized crossover design. Subjects acted as their own controls and were assigned to the two experimental conditions (resting and exercise), 1 week apart, in a counter-balanced order. Subjects Ten elite, male soccer players participated voluntarily in the study and all subjects were well trained and had a history of regular exercise for at least 5 years with an exercise frequency of at least 3 times a week. Written informed consent was obtained from all subjects before participation. The participants completed a health screen and a physical activity questionnaire. Individuals were recruited only if they met the following criteria: were non-smokers, were not currently on a weight gain/weight loss diet, had not been on any diet during the previous six month, had maintained a stable weight in the previous six month, had no gastric or digestive problems, and had no known history of cardiovascular disease. The experimental protocol was approved by the ethical board of the Abant Izzet Baysal University School of Medicine Clinical Laboratory Research, Bolu, Turkey, and the Institutional Review Board of Lehman College, The City University of New York, USA and was performed in accordance with the principles of the Declaration of Helsinki. The characteristics of the subjects at baseline are shown in Table 1. Specific procedures Dietary protocol Participants were asked to maintain their normal dietary and physical activity programs throughout the duration of the study. Subjects refrained from exercise, alcohol and caffeine 24 h before testing. Because energy balance and macronutrient intake can influence hunger, satiety, and feeding behavior, it was important to provide the same diet during the 24 h before each testing day. Throughout the day before the first main trial, participants' weight and food intake were recorded. Participants then replicated this food intake during the day before the second main trial. Participants were also provided with a standardized evening meal and asked to eat it at around 08:00 pm on the day preceding each of the study days. The dietary intake was analyzed by using a diet analysis software (Diet Analysis Plus©, Version 4.0, ESHA Research, Salem, OR). Preliminary test Resting energy expenditure Resting energy expenditure (REE) was measured for the purpose of estimating daily energy requirements. On trial days, participants arrived at the laboratory at 08:00 am. REE was measured between 08:15 and 09:00 am after an overnight fast. Upon arriving at the laboratory, the subject would lie in a supine position on a bed for 30 min to acclimatize to room temperature and undergo familiarization with the equipment and procedures. REE measurements were performed for 10 min after a 30 min rest period in a lit room at a comfortable temperature setting (20-24 °C). Oxygen consumption (VO2, mL·min-1) and carbon dioxide production (VCO2; mL·min-1) were measured every 10s by Cortex II Metalyser gas analyser II (Cortex Biophysik, Leipzig, Germany). REE was calculated using the Weir equation: REE (kcal·day-1) = [3.94 (VO2) + 1.11 (VCO2)] 1.44 (Weir, 1990). Anthropometric measurements Height was measured to the nearest 0.1 cm using a Holtain fixed wall stadiometer. Body mass was measured to the nearest 0.01 kg using a beam balance. BMI was calculated as weight in kilograms divided by the square of height in meters. Waist circumference was measured with a soft tape, midway between lowest rib and iliac crest. Hip circumference was measured over the widest part of the gluteal region, and waist-to-hip ratio was calculated accordingly. Skinfold thickness was measured at four sites (triceps, biceps, subscapular and suprailiac) on the right-hand side of the body using calipers (Skinfold Caliper Baseline MM, Fabrication Enterprise Incorporated, New York, US). Several trials were repeated until three tests yielded a difference of less than 0.5%. Body density was calculated using a four -site formula (Durnin and Womersley, 1974) and percent body fat was then estimated using the Siri equation (Siri, 1961). All body weight measurements were obtained with subjects wearing shorts and a tee-shirt, without shoes. Maximal aerobic capacity Maximal oxygen uptake test was performed one week before the main trials. The subject's VO2max was assessed during a graded exercise treadmill (HP Cosmos Mercury Med 4.0) test using standard Bruce protocol (Bruce et al., 1973) in the morning hours. The test was terminated when subjects stated they could no longer continue with the maximum workload. At the terminal workload, all subjects had to meet at least two of the following criteria for a valid test: (1) a final respiratory exchange ratio (RER) > 1.0, (2) O2 consumption increased by < 2 ml·kg-1 with an increase in exercise intensity, (3) attainment of >85% of age-predicted maximal heart rate. Respiratory gases were collected and analyzed throughout the entire exercise session with the use of a computer controlled breath-by- breath analyzer Cortex II Metalyser (Cortex Biophysik, Leipzig, Germany). The highest achieved value for oxygen consumption was considered the subject's VO2max. Heart rate (HR) was measured continuously throughout the test using a commercially available HR monitor (Polar S725X, Polar Electro, Finland). Main trials Participants were given at least one week to recover from the preliminary exercise tests before performing two main trials (exercise and control) in a random, crossover design with an interval of at least one week between trials. After fasting overnight, the participants came to the laboratory at 08:00 am and an intravenous catheter was inserted into an antecubital vein (08:15 am). At 08:50 am, 10 min prior to exercise, resting blood samples were collected from the catheter. In the exercise trial, subjects completed the treadmill exercise protocol at two speeds predicted to elicit a specific VO2: 50% VO2max for 105 min and 70% VO2max for 15 min. Adjustments were made to the treadmill speed if it was necessary. For the control trial, participants rested for the entire duration of the trial. Blood samples were collected at baseline and at 60, 120, 180 and 240 min after baseline for the determination of leptin, acylated ghrelin, insulin and glucose. All blood samples were collected while subjects lay in a semisupine position with the exception of the 60 min sample during the exercise trial; this sample was collected while subjects straddled the treadmill. Heart rate was recorded every 5 s during the treadmill exercise. Oxygen consumption and carbon dioxide production were measured every 10 s during the 2 h exercise using a Cortex II Metalyser and the mean respiratory exchange ratio (RER) was calculated from the recorded measurements. The energy expended during the exercise and resting sessions (t = 0-120 min) was calculated using the Weir equation (Weir, 1990). The analyzer was calibrated before the test with gases of known concentration according to manufacturer's guidelines. After the resting/exercise intervention (t = 120-240 min), participants stayed in the clinical investigation unit, but were free to write/read quietly. One hour after the end of the exercise/resting intervention (t = 180 min), participants were placed in individual booths, and presented with a buffet test meal. A diagram detailing the experimental session is shown in Figure 1. Subjective measurements of hunger Ratings of subjective feelings of hunger were reported on 100 mm visual analogue scales (VAS) at baseline and at 60, 120, 180, 240 min after baseline, as described previously (Flint et al., 2000). For hunger assessment, on one end (0 mm) of the scale was the descriptor "not at all hungry" and on the other extreme (100 mm) was the descriptor "totally hungry". Relative energy intake Relative energy intake (REI) was calculated as follows: REI = EI - [ECE - (exercise time x REE)] and for control trial: REI = EI - (exercise time x REE) where EI is the energy intake during the buffet-type meal, ECE is the measured energy cost of exercise, and REE is the measured pre-exercise resting energy expenditure (Pomerleau et al., 2004). Buffet test meal After 180 min (3 hours after the start of each trial) at 12.00 pm, all subjects were given a buffet test meal that they had to eat until reaching satiety. The buffet test meal consisted of a standardised buffet available ad libitum, in excess of expected consumption (4200 kcal, 53% carbohydrates, 12% protein and 35% fat), with a variety of lunch-type foods (sandwiches, yogurt, fruit, salad, cake, cookies, milk, and chocolate bar). The buffet foods were weighed/counted before participants sat down to the meal and reweighed/recounted after each subject had finished eating, and energy intake calculated. The energy content of the items consumed was ascertained using manufacturer values and was analyzed by using diet analysis software (Diet Analysis Plus©, Version 4.0, ESHA Research, Salem, OR). Participants were encouraged to consume the meal within 15 min and kept to the same start and finish times on both trials. Water was available ad libitum during trials, and the volume and time of ingestion were recorded. Blood biochemistry Blood samples were drawn into chilled tubes containing Na2EDTA (1.25 mg/ml) and aprotinin (500 TIU/ml (Kallikrein İnhibitor Unit), Phoenix, Burlingame, USA). Immediately after collecting blood samples, ghrelin tubes were centrifuged at 1500g for 15 min at 4°C. The obtained plasma samples were mixed with 1 mol/L HCl (Hydrochloric acid) at a ratio of 1/10 and were stored at -70°C until assayed. Samples for glucose were immediately centrifuged, and the plasma was separated and kept on ice for processing that day. Plasma glucose levels were measured using a Abbott-Architect C8000 (Abbott Laboratories, Illinois, USA) automated analyser by an enzymatic assay involving hexokinase and glucose-6- phosphate dehydrogenase. Blood samples for leptin and insulin hormone were drawn into red cap tubes were centrifuged after completion of clot formation and the serum samples were stored at -70°C until the day of the hormone measurements. Serum leptin concentration was measured using a commercial sandwich enzyme-linked immunosorbent assay (ELISA; DRG Leptin EIA-2395; DRG International Inc., Marburg, Germany) with a limit of detection of 1.0 ng/ml. The intra- and inter-assay coefficients of variation were 6.91% and 8.66%, respectively. Serum insulin concentration was measured using a ultrasensitive enzyme immunoassay (ELISA; DRG Insulin EIA-2337; DRG International Inc., Marburg, Germany) with a limit of detection of < 0.07 mU/l. The intra- and inter-assay coefficients of variation were 5.1% and 1.8%, respectively. Plasma acylated ghrelin assay was performed using a commercially available ELISA (SCETI Acylated Ghrelin EIA-97751; SCETI Co., Ltd., Tokyo, Japan) with a detection limit of 2.5 fmol/ml. The intra- and inter-assay coefficients of variation were 5% and 10%, respectively. At each blood sampling point, duplicate 20 μL blood samples were collected into micropipettes for the measurement of hemoglobin concentration and triplicate 20 μL blood samples were collected into heparinised microhaematocrit tubes for the determination of hematocrit. Hemoglobin and hematocrit values were used to assess plasma volume changes (Dill and Costill, 1974). Statistical analysis Statistical analysis was carried out using SPSS version 15. 0 (SPSS, Inc., Chicago, IL, USA). All the variables were checked regarding their normal distribution using the Shapiro-Wilk test and data are presented as means ±SD. Area under the curve (AUC) values for acylated ghrelin, glucose, insulin, leptin and hunger were calculated using the trapezoidal rule. Paired sample t-tests were used to assess differences between baseline and area under the curve values for each of these variables on the control and exercise trials. A repeated-measures, two factor ANOVA was used to examine differences between the two trials over time for acylated ghrelin, glucose, insulin, leptin, hunger and plasma volume change. Between-trial differences at each time point were examined using one-way ANOVA and Bonferroni post hoc tests when significant interactions were found. Mauchley's test was conducted to examine sphericity for the repeated measures analyses. If the assumption of sphericity was violated, the Greenhouse-Geisser adjustment was used to protect against type I error. Differences in absolute and relative energy intake at the buffet lunch between the two experimental conditions were assessed using paired sample t-tests. For correlation analysis, the Pearson coefficient was calculated. Plasma volume changes did not differ significantly between trials, and the unadjusted values are presented. Statistical significance was accepted at the 5% level. | |