Effect of combined use of a low-carbohydrate, high-protein diet with omega-3 polyunsaturated fatty acid supplementation on glycemic control in newly diagnosed type 2 diabetes: a randomized, double-blind, parallel-controlled trial

Background: The combined effect of a low-carbohydrate, high-protein (LCHP) diet and omega-3(n-3) polyunsaturated fatty acid (PUFA) supplementation on patients with type 2 diabetes (T2D) is not known. Objective: The aim of this study was to evaluate the effect of an LCHP diet combined with omega-3 (LCHP+omega-3) on glycemic control in patients with T2D. Design: In this randomized, double-blind, parallel-controlled trial, 122 newly diagnosed participants with T2D were randomly assigned to receive a high-carbohydrate, low-protein diet with low omega-3 PUFAs [control (CON)], an LCHP, omega-3, or LCHP+omega-3 diet for 12 wk. The ratio of carbohydrate to protein was 42:28 in the LCHP and LCHP+omega-3 diet and 54:17 in the CON and omega-3 diet. The participants were given 6 g fish oil/d (containing 3.65 g docosahexaenoic acid, eicosapentaenoic acid, and docosapentaenoic acid/d) in the omega-3 and LCHP+omega-3 diet groups or 6 g corn oil/d (placebo) in the CON and LCHP diet groups. Results: Compared with the CON diet group, greater decreases in glycated hemoglobin (HbA1c) and fasting glucose were observed in all of the other 3 diet groups at 12 wk. Of note, HbA1c reduction in the LCHP+omega-3 diet group (-0.51%; 95% CI: -0.64%, -0.37%) was greater than that in the LCHP (P = 0.03) and omega-3 (P = 0.01) diet groups at 12 wk. In terms of fasting glucose, only the LCHP+omega-3 diet group showed a significant decrease at 4 wk (P = 0.03 compared with CON). Moreover, the reduction in fasting glucose in the LCHP+omega-3 diet group (-1.32 mmol/L; 95% CI: -1.72, -0.93 mmol/L) was greater than that in the LCHP (P = 0.04) and omega-3 (P = 0.03) diet groups at 12 wk. Conclusions: The LCHP+omega-3 diet provided greater effects on HbA1c and fasting glucose and faster effects on fasting glucose than both the LCHP and omega-3 diets, indicating the potential necessity of combining an LCHP diet with omega-3 PUFAs in T2D control.