To swim or not to swim after eating: a randomized controlled crossover feasibility trial

Background: The aim was to investigate and challenge the belief that swimming immediately after eating is dangerous and also to investigate what potentially could happen when swimming immediately after a meal. We wanted to explore feasibility and get background data to perform sample size calculations and choose outcome parameters for a full-scale randomized trial. Methods: The trial was performed during lunch breaks at a medical writing course in Turkey in June 2022. Participants were randomised on the first trial day to swim 14 meters breaststroke immediately after lunch or wait 30 minutes after eating, with crossover on the second trial day. Main outcomes measures were mortality, mood, discomfort, and adverse events were assessed in participant-reported questionnaires. Participants completed a Profile of Mood States-Adolescents questionnaire, a visual analogue scale for discomfort, and a questionnaire of adverse events after each swim. Results: A total of 26 participants completed the trial. No cases of mortality, drowning, resuscitation, side stitch, or muscle cramps were reported. The participants reported no significant difference in their mood states after each swim and no significant difference was found regarding the participants' swimming time (P = 0.53). However, more discomfort was reported when swimming immediately instead of 30 minutes after eating (P = 0.05). Conclusions: It seems that swimming after eating is safe since no mortality or cramps were registered. However, a significant level of discomfort was found when swimming immediately after eating lunch. This feasibility trial provides background data for a future full-scale randomized trial.