Effects of basic carbohydrate counting versus standard dietary care for glycaemic control in type 2 diabetes (The BCC Study): a randomised, controlled trial

Background: Clinical guidelines recommend basic carbohydrate counting (BCC), or similar methods to improve carbohydrate estimation skills and to strive for higher consistency in carbohydrate intake potentially improving glycaemic control. However, evidence for this approach in type 2 diabetes (T2D) is limited. Objective: To examine the efficacy of a structured education program in BCC as add-on to standard dietary care on glycaemic control in individuals with T2D. Methods: The BCC Study was a randomized, controlled, open-label, parallel-group trial. Individuals with T2D aged 18-75 years with glycated haemoglobin A1c (HbA1c) 53-97 mmol/mol (7.0-11.0%) were randomly assigned (1:1) to BCC or standard dietary care. The primary outcomes were differences in changes in HbA1c or glycaemic variability (calculated as mean amplitude of glycaemic excursions [MAGE]) between groups after six months of intervention. Results: Between September 2018 and July 2021, 48 participants were randomly assigned, 23 to BCC and 25 to standard dietary care. Seven participants did not receive the allocated intervention. From a baseline-adjusted mean of 65 mmol/mol (95% CI 62-68 [8.1%, 7.8-8.4]), HbA1c changed by -5 mmol/mol (-8 to -1 [-0.5%, -0.7 to -0.1]) in BCC and -3 mmol/mol (-7 to 1 [-0.3%, -0.6 to 0.1]) in standard care with an estimated treatment effect of -2 mmol/mol (-7 to 4 [-0.2%, -0.6 to 0.4]); p = 0.554. From a baseline-adjusted mean of 4.2 mmol/l (3.7 to 4.8), MAGE changed by -16% (-33 to 5) in BCC and by -3% (-21 to 20) in standard care with an estimated treatment effect of -14% (-36 to 16); p = 0.319. Only median carbohydrate estimation error in favour of BCC (estimated treatment difference -55% (-70 to -32); p < 0.001) remained significant after multiple testing adjustment. Conclusions: No glycaemic effects were found but incorporating BCC as a supplementary component to standard dietary care led to improved skills in estimating carbohydrate intake among individuals with T2D.