Omega-3, omega-6, and total dietary polyunsaturated fat for prevention and treatment of type 2 diabetes mellitus: systematic review and meta-analysis of randomised controlled trials

Systematic review and meta-analysis of randomized controlled trials in adults aged 18 years and older at risk of diabetes, including healthy participants and people with diagnosed diabetes or impaired glucose metabolism. Studies were done in community settings and excluded pregnant or acutely ill participants.

Randomized trials evaluated increased intake or supplementation with long-chain omega-3 fatty acids, alpha-linolenic acid, omega-6 fatty acids, or total polyunsaturated fatty acids (PUFA). Long-chain omega-3 dosing in the included trials ranged from 2.4 to more than 4.4 g/day.

Increasing long-chain omega-3, alpha-linolenic acid, omega-6, or total PUFA had little or no effect on prevention or treatment of type 2 diabetes or on glucose metabolism. Long-chain omega-3 did not reduce diabetes diagnosis, with RR 1.00 (0.85 to 1.17) in 58,643 participants across 17 trials. Effects on HbA1c, fasting glucose, fasting insulin, and HOMA-IR were generally near zero for long-chain omega-3 and alpha-linolenic acid, and omega-6 or total PUFA also showed no clinically important benefit. The authors concluded that supplemental long-chain omega-3 should not be encouraged for diabetes prevention or treatment; if used to lower triglycerides, doses below 4.4 g/day are advised.

Evidence was uneven across interventions, with far fewer trials and participants for alpha-linolenic acid, omega-6, and total PUFA than for long-chain omega-3. Several outcomes were based on small numbers of trials, and study populations, doses, and follow-up periods varied substantially, limiting precision and generalizability. Some analyses were imprecise and relied on surrogate metabolic outcomes rather than hard diabetes endpoints.