To the Editor: We read with great interest the recently published paper by Thomsen et al [1]. As the authors report, in participants with type 2 diabetes, a carbohydrate-reduced high-protein diet (CRHP) could improve glycaemic control beyond the effects of weight loss compared with a conventional diabetes diet (CD) [1]. However, several issues described in this article warrant further discussion.

First, an energy-reduced high-protein diet could not significantly improve HbA1c or lipids compared with other energy-reduced diets in individuals with type 2 diabetes in RCTs with a duration of 1 [2] or 2 years [3]. Moreover, the effects of weight loss were similar between a high-protein diet and other energy-reduced diets [3, 4].

Second, weight loss is known to improve glucose control and reverse type 2 diabetes [5]. A 5.9% weight loss at 6 weeks was quite strong in this study [1]. It should be noted that the percentage of total weight loss at 6–12 weeks was usually higher than at 12 months in other long-term randomised controlled trials [3, 6, 7]. Weight regain was common and may affect glycaemic control results [8]. Additionally, the HbA1c reductions could not achieve a new steady state in 6 weeks [1]. The results of this 6 week intervention has limitations; a 24 or 48 week follow-up period might be more meaningful.

Third, the hypoglycaemic events in participants on the CRHP diet were asymptomatic, probably because the study diets were well designed and provided by the investigators [1]. When individuals with type 2 diabetes prepare the CRHP diet on their own, the risk of hypoglycaemic events might be increased and the safety of a CRHP diet used in everyday life tempered.

In conclusion, the CRHP diet for 6 weeks may improve HbA1c in individuals with type 2 diabetes; however, a long-term follow-up might be more meaningful.