Metabolic Effects of Fish-Oil Supplementation in Patients With Impaired Glucose Tolerance

To determine the impact of fish-oil supplementation on glucose and lipid metabolism in patients with impaired glucose tolerance (IGT), 30 ml fish oil containing 3.8 g eicosapentaenoic acid (EPA; 20:5 ω 3) and 2.5 g docosahexaenoic acid (DHA; 22:5 ω 3) were given to eight obese subjects with IGT (mean ± SD age 50.3 ± 8.0 yr) in addition to their regular diet for 2 wk. Studies were performed in randomized order versus an isocaloric control period with a washout phase of 3 wk. Hyperinsulinemic clamp examinations (1 and 10 mU · kg⁻¹ · min⁻¹) were performed. Glucose disposal rate (M value) rose from basal 14.3 ± 5.1 to 17.9 ± 4.4 μmol · kg⁻¹ · min⁻¹ after fish oil (P < 0.001) during the 1-mU clamp, whereas no change was seen during the 10-mU clamp (without fish oil, 42.2 ± 8.9 μmol · kg⁻¹ · min⁻¹; with fish oil, 45.1 ± 9.8 μmol · kg⁻¹ · min⁻¹;NS). Basal hepatic glucose output remained unaffected by fish oil, whereas fractional glucose clearance after intravenous glucose loading (2.4 mmol/kg body wt, t = 30 min) tended to increase (K value: without fish oil, 2.15 ± 1.02%/min; with fish oil, 2.74 ± 1.26%/min; NS). Neither the fasting concentrations of glucose and insulin nor induced glycemia and insulin response during intravenous glucose loading calculated as incremental area under the curve changed after fish-oil supplementation. Supplementation of ω-3 fatty acids led to a mean decrease in total cholesterol of 15.2% (5.78 ± 1.19 to 4.90 ± 0.83 mM, P <0.02), low-density lipoprotein cholesterol of 20% (4.14 ± 1.00 to 3.36 ± 0.90 mM, P <0.02), apolipoprotein B concentration of 16% (1.25 ± 0.43 to 1.06 ± 0.30 g/L, P < 0.05), and total serum triglycerides of 41% (1.71 ± 0.79 to 1.02 ± 0.39 mM, P < 0.05). High-density lipoprotein cholesterol remained unchanged. Because whole-blood viscosity consistently fell, probably due to an increased erythrocyte deformability, the observed changes in lipid metabolism and blood rheology may also help reduce cardiovascular risk factors in subjects with IGT.