Supplementation with a blend of krill and salmon oil is associated with increased metabolic risk in overweight men.

Randomized, double-blind, controlled crossover trial in overweight, otherwise healthy middle-aged men in Auckland, New Zealand. Participants were men only, with mean age 46.5 ± 5.1 years, BMI 25-30, and 87% of European descent; 51 men were recruited and 47 were analyzed.

Participants took 5 oral 1000-mg capsules daily of KS oil for 8 weeks in a randomized crossover design, with an 8-week washout between periods. The blend contained krill oil (88%) and salmon oil (12%); each capsule provided 46 mg EPA and 31 mg DHA, for a total daily dose of 5 g KS oil and about 400 mg n-3 PUFAs (230 mg EPA plus 154 mg DHA). The comparison was a control oil.

KS oil was associated with worse insulin sensitivity and a more adverse metabolic profile than control oil. The primary Matsuda index was lower with KS oil than with control oil (4.57 vs 5.33; P = 0.049), and the difference remained after adjustment for omega-3 index (4.04 vs 5.53; P = 0.009). Within-group KS-oil changes also showed an 18% decrease in Matsuda index (P = 0.002), a 0.39 increase in HOMA-IR (P = 0.016), and a 1.39 mU/L increase in fasting insulin (P = 0.048). Most secondary outcomes were not significantly different, although apolipoprotein B was higher with KS oil (P = 0.053) and carotid intima-media thickness trended upward (P = 0.068). Fishy burps were common with KS oil (22 participants, 47%) versus control oil (1 participant, 2%), and urticarial reactions occurred in 2 participants (4%) receiving KS oil.

The trial was small, short term, and limited to overweight men, which reduces generalizability. Secondary outcome findings were largely null or only trend-level, and some interpretation relies on post hoc within-group analyses and mediation modeling. Because the intervention was a blend, it is unclear whether the adverse effects were driven by krill oil, salmon oil, or other constituents.