Effects of a nutritional supplement containing fish protein, vitamin D, and ω3 fatty acids, taken during high-intensity functional training, on physical performance in recreationally trained individuals: a randomized controlled trial

Purpose Research on supplementation during high-intensity functional training (HIFT) is limited. We examined the effects of a multi-ingredient supplement containing fish protein, vitamin D, and ω3 fatty acids, taken during HIFT, on physical performance in trained individuals. Methods Twenty-five recreationally trained participants (14 females, 11 males) underwent 6 weeks of HIFT (3 times/week) while taking each of three supplements, separated by 2-week washout periods in a researcher-blinded, randomized, triple-crossover, and counterbalanced fashion. The supplements and daily doses were (a) 0.6 g fish protein/kg body mass, 21 μg vitamin D, and 1.8 g ω3 fatty acids [including 1.4 g eicosapentaenoic (EPA) and docosahexaenoic acid (DHA)], (b) 0.6 g/kg whey protein, and (c) 0.6 g/kg maltodextrin. Participants followed isoenergetic diets providing 1.0 g protein/kg body mass, 30 μg vitamin D, and 0.2 g EPA and DHA daily. Training variables were assessed during the 1st and 6th weeks of each intervention period. Endurance and strength variables were measured before and after each intervention period. Data were analyzed using 2-way repeated-measure ANOVA (supplement × training). Results HIFT augmented workout duration per training session ( p = 0.007). One-repetition maximum and maximal force of shoulder press, as well as strength endurance of core muscles, increased by 3–6% with training ( p < 0.001). Supplementation did not affect any of these adaptations. Conclusions Six weeks of HIFT improved some training and performance variables in recreationally trained adults. However, increasing the intake of protein, vitamin D, and ω3 fatty acids did not influence the variables assessed. Trial Registation Number: NCT05402527 (22/4/2022), clinicaltrials.gov.