Does fish oil help with obesity? What the research does and doesn't show

The evidence doesn't support fish oil as a weight-loss aid. The most focused meta-analysis on the question — 11 trials, 617 people — found no difference in body weight between omega-3 and placebo groups, though it did find a modest reduction in waist circumference and triglycerides.

What the evidence doesn't support

It doesn't support fish oil, on its own, as something that reduces body weight or body mass index — the dedicated meta-analysis below found no significant difference from placebo on either measure. It doesn't support fish oil as a substitute for a calorie deficit or exercise for fat loss; the one modest effect found in the research below only showed up when omega-3 was added to an existing exercise program, not on its own.

What the trials found

A 2017 meta-analysis in the Journal of Nutrition, Health and Aging pooled 11 randomized controlled trials in 617 overweight and obese adults. Across 9 studies measuring body weight directly, there was no significant difference between omega-3 and placebo groups. Across 7 studies, waist circumference was significantly reduced. Triglyceride levels also fell significantly. Body mass index, total cholesterol, LDL, HDL and fasting glucose showed no significant change. The review's own authors called the evidence inconclusive given the small number and mixed quality of the trials available, and asked for a larger, better-designed trial.

A 2025 systematic review and meta-analysis in Clinical Nutrition ESPEN looked specifically at what omega-3 adds on top of an existing exercise program, pooling 21 studies and 673 adults with a body mass index of 24 to 37. Compared with exercise training alone, adding omega-3 to exercise training reduced fat mass by about 1 kilogram on average, along with modest reductions in triglycerides and blood pressure. Omega-3 added no measurable benefit for body weight, body mass index, lean body mass, or several other outcomes measured, beyond what exercise training alone already produced.

Questions people ask

Can fish oil help you lose weight?

The dedicated trial evidence says no, not on its own. The most focused meta-analysis (11 trials, 617 people) found no significant difference in body weight between omega-3 and placebo, though waist circumference and triglycerides did drop.

Does fish oil help with weight loss when combined with exercise?

A 2025 review found a modest additional reduction in fat mass (about 1 kilogram) when omega-3 was added to an exercise program, compared with exercise alone — but no additional change in overall body weight.

What's the best time to take omega-3 for weight loss?

Neither of the two reviews above tested timing as a variable, and neither found a body-weight effect to time in the first place. There's no trial evidence to point to one time of day as more effective for this specific use.

When to talk to a doctor

A diagnosis of obesity, or a weight-loss goal tied to a health condition, is worth discussing with a doctor who can weigh options with an actual evidence base behind them. Fish oil is not a treatment for obesity or a substitute for the diet, activity or medical changes a doctor might recommend, and nothing in the evidence above supports using it that way. If you take medication, or are pregnant or nursing, talk to a doctor before adding any supplement.

Related reading: fish oil, diabetes and PCOS: what the research does and doesn't show, how much fish oil should you take a day, and fish oil benefits: what the research does and doesn't show.