DHA-enriched fish oil reduces insulin resistance in overweight and obese adults

Adipose tissue inflammation is major factor in the development of insulin resistance (IR). Long-chain omega-3 polyunsaturated fatty acids (LCn-3PUFA) docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are anti-inflammatory bioactive lipids, thus may protect against type 2 diabetes (T2D) development. Previous research has demonstrated a sex-dependent association between LCn-3PUFA and T2D, and evidence suggests LCn-3PUFA may improve IR in a sex-dependent manner. This double-blind, randomized, parallel-arm placebo-controlled study aimed to determine whether DHA-enriched fish oil (FO) supplementation improves IR. Sex-dependent effects were assessed by testing for an interaction between sex and treatment in the multiple regression models. Men and women with abdominal obesity (waist circumference: males, ≥102 cm; females, ≥88 cm) and without diabetes were recruited from the community. Participants (age: 50.9 ± 12.7 years, female: 63.7%, BMI: 32.4 ± 6.6 kg/m²) were randomly allocated to either 2 g FO (860 mg DHA + 120 mg EPA) (intervention, n = 38) or 2 g corn oil (CO) /day (control, n = 35) for 12 weeks in a double-blind randomised controlled trial. A fasting blood sample was collected at 0 and 12 weeks for assessment of IR, glucose and blood lipid profile. Sixty-eight participants completed the intervention. Compared with CO (n = 32), FO (n = 36) significantly reduced fasting insulin by -1.62 μIU/L (95%CI: -2.99, -0.26,) (p = 0.021) and HOMA-IR by -0.40 units (95%CI: -0.78, -0.02, p = 0.038). Higher insulin and HOMA-IR at baseline were associated with greater reductions in the FO group (p < 0.001). There was no interaction between sex and treatment for the change in insulin (p-interaction_{sex*treatment} = 0.816) or HOMA-IR (p-interaction_{sex*treatment} = 0.825). DHA-enriched FO reduces IR in adults with abdominal obesity, however, sex-dependent differences were not evident in this study.