The effect of artificial sweeteners on substrate utilisation at rest and during sub-maximal exercise in recreationally active adults (a Pilot Study)

This study investigates the effect of artificial sweeteners (AS) on substrate utilisation at rest and during exercise. In a randomised, counter-balanced crossover design, each participant will complete three experimental trials following a VO2max test. Participants will consume one of three beverages across three sessions: Artificially sweetened sports drink Full-sugar sports drink Water (control condition) Each beverage will be consumed in a total volume of 1000mL, administered in three doses: 500mL prior to exercise, followed by 250mL at 15 minutes and 250mL at 25 minutes during the exercise protocol. The artificially sweetened sports drink used is Gatorade Sports Drink Sugar Free Grape Electrolyte Hydration Bottle, containing sucralose (955) and acesulfame potassium (950) as sweeteners, with 0g carbohydrate. The full-sugar drink is the standard Gatorade Grape Electrolyte Hydration Bottle, containing approximately 60g carbohydrate per 1000mL, derived from sucrose and glucose. The water condition serves as the control, with no caloric content. All beverages are administered one-on-one by a researcher (Exercise Physiologist Honours Student) in a laboratory setting. Adherence is monitored through direct observation of beverage intake and collection of empty bottles to ensure full consumption. Exercise Component Visit 1 – VO2max Test and Familiarisation Participants complete an incremental VO2max test using a progressive ramp protocol on a cycle ergometer, with the aim of determining their maximal aerobic capacity and lactate threshold (LT). Starting at 10% estimated Wmax, load increases by 10% per minute until volitional exhaustion. Continuous gas exchange analysis is performed using a COSMED metabolic cart. Heart rate, blood glucose, blood lactate, and blood pressure are assessed pre- and post-test. A 5-minute active recovery is followed by a 20-minute familiarisation ride at 50% Wmax to practise sampling procedures. Visits 2–4 – Submaximal Trials (Beverage Conditions) After the 7-day washout following Visit 1, participants complete three 90-minute experimental trials, each associated with one beverage condition. Exercise is performed on a cycle ergometer, with workload prescribed based on individual LT derived from Visit 1. Pre-Exercise Phase Participants consume 500mL of the assigned beverage upon arrival. This is followed by 10 minutes of resting data collection, and 20 minutes of post-beverage metabolic assessment, including gas exchange and finger-prick blood glucose and lactate. Exercise Protocol Warm-up: 10 minutes at 25% LT Main trial: 40 minutes continuous cycling at 90% LT, with two additional beverage doses (250mL at minutes 15 and 25), and monitoring of gas exchange, heart rate, Borg RPE, and blood lactate/glucose every 10 minutes Cool-down: 10 minutes at 20% LT, followed by final physiological measures All sessions are supervised by no fewer than two trained researchers to ensure safety, consistency, and protocol fidelity. A minimum 7-day washout period is observed between each beverage condition.