Impact of Protein Content of Milk on Post-Exercise Appetite and Energy Intake

The primary objective of this randomized, double-blind, crossover clinical trial is to evaluate the acute effects of post-endurance exercise consumption of milk beverages with varying protein content on subjective appetite, circulating appetite-related hormones, and subsequent ad libitum energy intake in healthy, recreationally active adult males. The study will recruit at least 12 healthy male participants aged 18-39 years who have been regularly engaged in endurance-based physical activity (e.g., cycling, running, triathlon, orienteering, team sports) for a minimum of one year, with a training frequency of at least three sessions per week lasting 60-90 minutes each. Participants will complete five laboratory visits under a crossover design with a minimum one-week washout period between intervention conditions. The first two sessions will consist of pre-study visits (screening, anthropometric assessments, VO₂max testing, and familiarization). The remaining three visits will involve the ingestion of one of the following beverages in a randomized order: standard-protein milk (0 g protein), high-protein milk (30 g protein), or an isoenergetic carbohydrate-based control beverage (0 g protein). All beverages will be isocaloric and isovolumetric and provided in opaque bottles to ensure double-blind conditions. On each intervention day, participants will perform a steady-state endurance exercise protocol using a calibrated cycle ergometer, followed immediately by the ingestion of one of the test beverages. Appetite will be assessed subjectively using validated Visual Analogue Scales (VAS) at predefined intervals. Venous blood samples will be collected to analyze concentrations of insulin and acylated ghrelin as objective biomarkers of appetite regulation. One hour after beverage consumption, an ad libitum test meal will be provided to quantify subsequent energy intake. The total caloric intake and macronutrient distribution will be recorded and analyzed. This study is designed to provide insight into the role of post-exercise milk consumption-specifically the influence of protein content-on short-term appetite modulation and energy intake regulation in recreationally trained individuals.

Inclusion criteria

• The study will include healthy, physically active male participants aged 18-39 years who have been engaging in recreational endurance sports (such as cycling, running, triathlon, orienteering, or team sports) for at least one year, with a minimum frequency of 3 sessions per week lasting 60-90 minutes.

Exclusion criteria

• Current smoker
• Chronic or excessive alcohol consumption
• Use of supplements and/or chronic medications that may affect appetite
• Presence of cardiac, hepatic, renal, pulmonary, neurological, hematological, gastrointestinal, diabetic, thyroid, or psychiatric disorders, and/or musculoskeletal conditions that may limit exercise participation
• Allergy or intolerance to any of the foods or beverages to be consumed during the study
• Unstable body weight (e.g., weight loss greater than 1 kg in the past week)
• Currently following a weight-loss diet
• Diagnosed eating disorders or individuals who cognitively restrict food intake (to be assessed using the Three-Factor Eating Questionnaire)