2.8. Intervention
BLIND
Participants allocated to CON were instructed to limit their caffeine intake to no more than approximately 100 mg per day and to refrain from the use of any performance-enhancing or thermogenic supplement for the duration of the four-week study. If participants were already using supplements for general health support (e.g., multivitamins, greens powders, creatine) they were told to continue these as before. Otherwise, participants in CON were instructed to maintain their habitual exercise and dietary patterns, including the types of foods consumed and the frequency of meals.Participants in PRO and PRO + FB were given the same instructions as CON but were also provided with additional supplements to consume for the duration of the four-week intervention. Both groups were provided with whey protein powder (OxyWhey Lean Wellness Protein, EHP Labs, Sydney, Australia) and were instructed to consume between one and three scoops per day based on measured body mass (1 scoop per day for participants between 50 and 59.9 kg, 2 scoops per day for participants between 60 and 89.9 kg, and 3 scoops per day for participants between 90 and 100 kg). Each 33 g scoop of the whey supplement contained approximately 130 kcal, 1.5 g fat, 2 g carbohydrate, and 25 g protein in addition to a variety of minerals, B-vitamins, and Vitamin C. Participants were instructed to consume the whey powder at any time of day and in any manner that was most conducive to daily consumption. In addition to the protein, participants were provided with either a powdered thermogenic supplement (OxyShred Thermogenic Fat Burner, EHP Labs, Sydney, Australia) or a visually identical placebo. As per instructions provided for the EHP Labs product, participants were instructed to begin taking one scoop of the supplement per day, either in the morning upon waking or 15 min before exercise. After one week, the participants were instructed to begin taking two scoops per day: one in the morning upon waking and the second in the early afternoon and/or 15 min before exercise. Each 4.5 g scoop of the commercially available thermogenic supplement consumed by PRO + FB contained 1 g carbohydrate and approximately 150 mg caffeine in addition to a number of vitamins, minerals, and other supplements with potentially lipolytic, mood-enhancing, and immunity-supporting properties. The full list of ingredients contained in the active supplement can be found in To encourage and monitor participant compliance throughout the four-week intervention, participants were asked to complete a brief daily online questionnaire (SurveyMonkey, Inc., San Mateo, CA, USA) to elicit data pertaining to their compliance with instructed protocols the day prior. Specifically, each day, all participants were asked whether they followed their normal exercise and nutrition habits as instructed. Participants in PRO and PRO + FB were also asked if they had consumed their assigned supplement as instructed. Four weeks after their baseline assessment, each participant returned to the laboratory to complete follow-up assessments for all body composition, anthropometry, RMR, and psychometric and subjective variables. In addition, to assess the efficacy of masking, participants in PRO and PRO + FB were asked to guess the condition to which they had been assigned. At the second visit, participants in PRO and PRO + FB were asked to report their daily habitual caffeine intake only from sources outside of the provided supplement. Therefore, after the blind was removed, 300 mg caffeine (the instructed intake for weeks two through four of the intervention) were added to the values reported at the second visit in the PRO + FB group only.