Influence of Fish Consumption and ω-3 Supplementation on the ω-3 Index of Young Adults: A 2 × 2 Factorial Randomized Controlled Trial (YouFish Study)

BACKGROUND: The omega-3 index (O3I), reflecting the percentage of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in erythrocyte membranes, is associated with reduced risk of cardiovascular disease (CVD). UK dietary guidelines recommend two portions of fish/week (280g/week) or supplementation of approximately 500 mg EPA+DHA/day for non/low fish consumers; however, the impact of these recommendations on the O3I is unclear. OBJECTIVE: The aim of this study was to explore the influence of the current guidance for fish consumption and omega-3 supplementation on the O3I amongst young adults. METHODS: Healthy adults aged 18-30 years (n=40) with low fish intake and O3I <6% were randomised to receive either two fish (one portion oily fish and one portion white fish) or two non-fish meals per week as well as a daily 700 mg EPA+DHA supplement capsule or placebo capsule for 8-weeks in a 2x2 factorial design. The effects on lipid profiles and high sensitivity C-reactive protein (hs-CRP) were also examined. RESULTS: Consumption of two portions of fish/week and omega-3 supplementation resulted in a significant mean % increase in O3I of 2.27±0.82% and 2.03±0.88%, respectively. Both interventions also significantly increased total erythrocyte n-3 PUFAs (+3.11±1.79% and +2.00±1.24%) and lowered total n-6 PUFAs (-1.94±1.65% and -2.60±1.16%) (all FDR p<0.05). There were no significant effects on blood lipids or hs-CRP. CONCLUSIONS: In support of current dietary guidelines for fish consumption and omega-3 intake, two portions of fish/week or omega-3 supplementation are effective strategies for increasing the O3I. These findings support the efficacy of current public health recommendations for fish consumption and omega-3 intake as early dietary interventions to reduce CVD risk through increasing the O3I amongst young adults. This trial was registered at www. CLINICALTRIALS: gov as NCT06729229.