Dietary strategies for patients with type 2 diabetes in the era of multi-approaches; review and results from the Dietary Intervention Randomized Controlled Trial (DIRECT)

Abstract

Dietary intervention is recognized as a key component in prevention and management of type 2 diabetes (T2DM) and the debate persists: which dietary strategy is most effective. In the Dietary Intervention Randomized Controlled Trial (DIRECT) 322 moderately obese participants were randomized for 2 years to one of three diet groups: low-fat, Mediterranean and low-carbohydrate. Differential effects were observed in the sub-group of patients with T2DM at 24 months: participants randomized to the Mediterranean diet, which had the highest intake of dietary fibers and unsaturated to saturated fat ratio, achieved greater significant improvements in fasting plasma glucose and insulin levels. Patients who were randomized to the low-carbohydrate diet, which had the minimal intake of carbohydrates, achieved a significant reduction of hemoglobin A1C. Although improvements were observed in all groups, the low-fat diet was likely to be less beneficial in terms of glycemic control and lipid metabolism. Interpretation of results from different studies on dietary strategies may be complex since there is often no consistency in diet compositions, calorie restriction, intensity of intervention, dietary assessment or extent of adherence in the trial. Nevertheless, it seems that low fat restricted calorie diets are effective for weight loss and are associated with some metabolic benefits; however, some recent trials have shown that low carbohydrate diets are as efficient in inducing weight loss and in some metabolic measures such as serum triglycerides and HDL-cholesterol may be even superior to low fat diets. When addressing the issue of diet quality rather than quantity applying the glycemic index may have some added benefits. Furthermore special features of the Mediterranean diet have apparent additional favorable effects for patients with T2DM.