A Theory of Planned Behaviour-Based Intervention on Dietary Supplement Use Among Varsity Athletes: A Pilot Randomized Controlled Trial

Background/Objectives: The rising prevalence of dietary supplement use among athletes raises concerns, given the risks associated with unnecessary or excessive use. This study evaluated the impact of a Theory of Planned Behaviour (TPB)-based online educational intervention, “Nutrition for Athletes”, on dietary supplement use among varsity athletes at a Canadian university. Methods: Thirty varsity athletes were randomized into intervention (n = 18) and control (n = 12) groups. The intervention was delivered online over four weeks and consisted of four units that covered topics related to sports nutrition, hydration in sports, dietary supplements, and risks associated with dietary supplement use. Dietary supplement use was measured at baseline and post-intervention using self-reported questionnaires. Results: The most commonly used supplements at baseline were vitamin D (57%), vitamin C (53%), sports drinks (50%), protein bars, powders, and shakes (43%), and whey protein (40%). Binary logistic regression revealed a reduced likelihood of dietary supplement use in the experimental group compared to the control group post intervention, but this difference was not statistically significant (OR = 0.18, 95% CI = 0.01 to 1.76, p = 0.14). There was also no significant change in the behaviour of dietary supplement use within the experimental group, when comparing baseline to post-intervention (OR = 0.12, 95% CI = 0.01 to 1.11, p = 0.06). Conclusions: These findings reflect the potential existence of an intention-behaviour gap. Future interventions may benefit from incorporating strategies that address control-related barriers.