Participants of the study were essentially healthy men with body mass index (BMI) ≤29 kg/m2 and aged between 22-35 years, recruited by advertisements and word of mouth. Study participants were required to be non-smokers, to have stable body weight for one month prior to study enrolment, and were not taking any medication, nutritional supplement or being on a special diet. Exclusion criteria included chronic illness, eating disorder and history of gastrointestinal operations which could interfere with the results of the study. Written informed consent were obtained prior commencing the study. The Ethics Committee of the collage of Medical Veterinary and Life Sciences, Glasgow University approved the study.

Preliminary session

Before joining the study, preliminary session was conducted for \~3 hours. Participants were informed to come to the metabolic research unit at New Lister Building, Glasgow Royal Infirmary to completed physical activity readiness questionnaire (PARQ), healthy screening questionnaire and International physical activity questionnaire. Only participants at light or moderate of physical activity level, answered "no" to all questions in PARQ and were in generally good health were eligible to complete the preliminary session. Subsequently, height and body mass were measured and a \~30 min submaximal exercise test was conducted at gradually increasing inclines. After 4 minutes of warming up period (3.5 km/hr and 0% incline), participants were walking at a constant speed of 6 km/hr with incline being increased by 2% every 4 min. The test was terminated when the heart rate (HR) reached 85% of maximal HR (HRmax) defined as 220 - age in years. During the test, participants were wearing a HR monitor and a face mask (to measure rate of oxygen consumption (V̇O2) and rate of carbon dioxide production (V̇CO2)). The HR monitor and the mask were both connected to the indirect calorimetry machine (Quark RMR®, COSMED, Italy). The obtained data was used to predict maximal oxygen consumption (V̇O2max) which was achieved by extrapolation of the HR against V̇O2 in order to calculate workload corresponds to 60% of V̇O2max.

Experimental trials

A randomisation scheme was generated using GraphPad Software 2018© to allocate participants to the experimental trials. Trials were marked as Control and Exercise by the researcher. Each participant started first trial according to allocated trial randomization. On the morning of each experiment trial, participants reported to the metabolic research unit between 08:00 and 09:00 after an overnight fast. Height, body mass and resting metabolic rate (RMR) were measured. A cannula was introduced into an antecubital vein and after an interval of 10 min, a baseline blood sample was obtained. Subsequently, an appetite questionnaire was completed. Participants were then asked to either resting (Control trial) or exercising (Exercise trial) for one hour. The Exercise trials were conducted under controlled laboratory conditions. Participants were exercising on the treadmill (Trackmaster Treadmills, Full Vision, Inc., Kansas, USA) at speed and grade corresponding to 60% of their V̇O2max. Participants were wearing a HR monitor and a face mask while exercising, connected to indirect calorimetry equipment (Quark RMR®, COSMED, Italy). V̇O2 and V̇CO2 in the inspired and expired air were measured to calculate fat and CHO oxidation and rate of physical activity energy expenditure (PAEE) by using indirect calorimetry equations described by Frayn and Macdonald (1997).

Subsequently, participants in both trials were presented to a standard isocaloric PKU type meal at 120 min. PKU meals in Exercise and Control trials were matched for weight content and macronutrient composition. Participants were asked to consume the entire meal within 20 min. Appetite questionnaires were obtained and blood samples were collected at 30, 60, 90 and 120 pre-meal, 150, 180, 210, 240 and 300 min post-meal. Metabolic rate was measured every 30 min after each blood sample. After the completion of the last measurement, the participants were presented with an ad libitum buffet test meal which used to assess, under laboratory conditions, the spontaneous macronutrient and energy intake (EI). After completion of each trial, participants required to record their EI for the remainder of the experimental day using a self-recorded food diary. Water was available throughout the trials, but intake was replicated in the second trial and consumption time was matched. During the two days before the first trial, participants weighed and recorded all foods and drinks consumed and were asked to replicate this intake during the two days preceding the second trial.