Foods, nutrients or whole diets: effects of targeting fish and LCn3PUFA consumption in a 12mo weight loss trial

Randomized controlled 12-month weight-loss trial in overweight to obese adults in Wollongong, Australia, with baseline data from 118 participants. Adults had BMI 25 to 37 kg/m2 and were midlife; randomization was stratified by sex and block randomized, and all groups received a hypocaloric diet and physical activity advice.

Participants in the Fish arm were advised to eat 2 fish meals per week, targeting 180 g of fatty fish weekly, for 12 months on top of a hypocaloric diet. Participants in the Fish + S arm received the same fish advice plus oral LCn3PUFA capsules providing 420 mg EPA and 210 mg DHA; control and Fish arms received placebo capsules containing 1 g olive oil per day.

The fish advice and LCn3PUFA supplement strategy did not improve weight loss beyond the hypocaloric diet. All groups lost weight at 12 months, with reported changes of Control -4.5 kg, Fish -4.3 kg, and Fish + S -3.3 kg, and there was no between-group effect on weight (group p = 0.682; interaction p = 0.326). The supplement arm did increase omega-3 status: at 12 months, the omega-3 index was 3.4 ± 1.0% in Fish versus 4.4 ± 1.6% in Fish + S, p = 0.007. Most cardiometabolic outcomes improved over time with the diet intervention, but these changes were not meaningfully different between groups.

The active intervention arms were modest in size and had substantial attrition, with only 25 Fish and 20 Fish + S completers for completers-only analyses and fewer participants contributing to some biomarkers. Adherence to the fish target was incomplete, and the trial bundled fish advice with a broad hypocaloric diet and physical activity advice, making the specific effect of fish or LCn3PUFA supplementation harder to isolate. Generalizability is limited to overweight to obese midlife adults from one Australian site.