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.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized controlled trials
PubMed 31434641 · doi:10.1136/bmj.l4697
What was done
The authors conducted a systematic review and random-effects meta-analysis of randomized controlled trials lasting at least 24 weeks that evaluated increasing alpha-linolenic acid (ALA), long-chain omega-3, omega-6, or total polyunsaturated fatty acids (PUFA) on diabetes diagnosis and markers of glucose metabolism (fasting glucose, fasting insulin, HbA1c, HOMA-IR). Databases searched included Medline, Embase, Cochrane CENTRAL, and trial registries. Quality and risk of bias were evaluated using the Cochrane tool and GRADE.
What was found
Eighty-three RCTs were included (10 at low summary risk of bias). Long-chain omega-3 had little or no effect on diabetes diagnosis (relative risk 1.00, 95% CI 0.85 to 1.17; 58,643 participants, 3.7% developed diabetes) or glycemic metabolism: HbA1c mean difference -0.02% (95% CI -0.07% to 0.04%), plasma glucose mean difference 0.04 mmol/L (95% CI 0.02 to 0.07), fasting insulin mean difference 1.02 pmol/L (95% CI -4.34 to 6.37), and HOMA-IR mean difference 0.06 (95% CI -0.21 to 0.33). Doses of supplemental long-chain omega-3 above 4.4 g/d suggested possible negative outcomes. The effects of ALA, omega-6, and total PUFA on diabetes diagnosis were unclear due to very low-quality evidence, though increasing ALA was associated with an increase in fasting insulin of about 7%. The omega-3/omega-6 ratio was not associated with diabetes or glucose metabolism.
Why it matters
This comprehensive systematic review indicates that increasing dietary or supplemental polyunsaturated fatty acids does not prevent type 2 diabetes or meaningfully improve glycemic control.
Limits
Only 10 of 83 included trials were at low summary risk of bias. Evidence regarding the specific effects of ALA, omega-6, and total PUFA on incident diabetes was very low quality due to limited trial data. Trials under 24 weeks in duration were excluded.
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