AimsThe role of carbohydrate restriction in the management of glycaemia in type 2 diabetes (T2D) has been a subject of immense debate and controversy partly due to low-carbohydrate trials being confounded by multiple factors including degree of calorie restriction, dietary protein content, and by no clear definition of a low-carbohydrate diet. The current study sought to provide insight into the relationship between carbohydrate restriction and glycaemia by testing the effect of varying doses of carbohydrate on continuous glucose concentrations within a range of intakes defined as low-carbohydrate while controlling for confounding factors.MethodsThis was a randomised crossover trial in participants with T2D testing 5 different 6-day eucaloric, isocaloric dietary treatments with varying carbohydrate contents (10%, 15%, 20%, 25%, and 30% kcal). Diets were kept isocaloric by exchanging %kcal from carbohydrate with predominantly unsaturated fat, keeping protein constant at 15% kcal. Daily self-weighing was employed to ensure participants maintained their weight throughout each treatment arm. Between dietary treatments, participants underwent a washout period of at least 7 days and were advised to maintain their habitual diet. Glycemic control was assessed using a continuous glucose monitoring device that was placed while the participant was on their normal diet, and was worn for the 6 days of each treatment.Results12 participants completed the study. There were no differences in 24-hour and postprandial sensor glucose concentrations between the 30%kcal and 10%kcal doses (7.4 ± 1.1mmol/L vs 7.6 ± 1.4mmol/L (P=0.28) and 8.0 ± 1.4mmol/L vs 8.3 ± 1.3mmol/L (P=0.28) respectively). In our exploratory analyses we did not find any dose-response relationship between carbohydrate intake and glycaemia. A small amount of weight loss occurred in each treatment arm (range: 0.4 to 1.1kg over the 6 days) but adjusting for these differences did not influence the primary or secondary outcomes.ConclusionsModest changes in dietary carbohydrate content in the absence of weight loss while keeping dietary protein intake constant do not appear to influence glucose concentrations in people with T2D.Trial RegistrationISRCTN 11067343.
