Postprandial Metabolic and Appetite Responses to Different Food Intake Sequences in Athletes

Participants will be required to visit the research facilities at Cidade do Futebol (Portugal Football School's headquarters) on three separate occasions, following a 10-12-hour overnight fast and abstaining from alcohol consumption and strenuous physical activity the day before (e.g. no exercise causing sweating or heavy breathing). Visits will be separated by a wash-out period of 7 days to ensure participants experience similar dietary and physical activity patterns in the 24 hours preceding the trials. Each visit is expected to last approximately 4 hours. In the screening and familiarisation visit, athletes will be asked to provide written informed consent to participate in the study and answer a series of questions to confirm their eligibility and safety for enrolment. Subsequently, an anthropometric assessment, blood pressure measurement, fasted blood collection and 2-hour 75-g oral glucose tolerance test (OGTT) will be performed to establish participants' baseline characteristics and analyse biochemical markers of the glucose and lipid metabolism to identify any further exclusion criteria (i.e., glycated haemoglobin (HbA1c); glucose; insulin; triglycerides; total, high-density lipoprotein and low-density lipoprotein cholesterol; haemogram and high-sensitivity C-reactive protein). To familiarise participants with the cannulation procedure ahead of the experimental trials, a trained and experienced nurse will insert a cannula (a small plastic tube) into a vein on the participants' arm, from which fasting and 2-h OGTT blood samples will be drawn (15 ml in total). Eligible participants will be instructed to monitor their diet and physical activity for 24 hours before their first experimental visit and replicate these patterns before the second experimental visit. In both experimental visits, participants will arrive at the research facilities between 8:00-9:00 and rest comfortably for 10 minutes. Body mass and blood pressure will be remeasured. Then, cannulation will be performed, and 18.5 ml venous blood samples will be drawn immediately before and at 30, 60, 90, 120, and 180 minutes after the meal challenge to assess postprandial changes in insulin, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), ghrelin, peptide YY (PYY), triglycerides, and non-esterified fatty acids (NEFA) concentrations. At similar timepoints, as well as at 15 and 45 minutes, capillary blood glucose will be measured using a finger prick glucometer, and appetite ratings will be marked by the athletes on 100-mm visual analogue scales. Upon completing the research assessments, participants will be asked to photograph and record the timing, type, and amounts of foods, drinks, and/or supplements consumed for an additional 3 hours to evaluate their prospective, ad libitum intake.