Effect of a low-carbohydrate diet on glycaemic control and disease management in type 2 diabetes: results from a prospective free-living trial

Background Low-carbohydrate diets (LCD) improve glycaemic control (HbA1c) and weight in individuals with type 2 diabetes (T2D). Few studies have explored both the quantitative effects and qualitative experiences of individuals following LCD. Methods Single-arm, prospective, observational study of a carbohydrate-reduced diet (CRD) on HbA1c, weight and the acceptability in people with T2D and HbA1c ≥6.5% (48 mmol/mol). Participants were recruited from general practitioner surgeries and enrolled in an eight-session CRD health coaching programme delivered by The Lifestyle Club, with follow-up over 6 months. Blood samples, anthropometric data and dietary adherence were measured at baseline and at 6 months. Participants were informed about the semi-structured interviews at consent and invited after visit 2. Results Forty-eight participants were included (mean age 67±10 years; 55% male). Carbohydrate intake decreased from 226.0 g/day at baseline to 126.3 g/day at 6 months (p<0.001) and the proportion of energy from carbohydrates decreased from 42.6% to 29.7% (p<0.001). HbA1c decreased from 60.0±12.9 mmol/mol to 49.7±9.0 mmol/mol at 6 months (p<0.001). Mean body weight decreased by 5.2±4.4 kg (p<0.001), and body mass index decreased from 30.6±6.5 kg/m² to 28.8±5.7 kg/m² (p<0.001). No significant changes were observed in lipids or blood pressure. Regression analyses showed an association between weight loss and HbA1c normalisation (OR 1.413, p=0.002), but no relationship was found between carbohydrate intake and changes in HbA1c. Qualitative interviews revealed that motivation and empowerment were central to adherence; participants cited health improvements and reduced medication as key motivators. Challenges included social dynamics and domestic routines; older participants and those with significant comorbidities reported greater difficulties in maintaining the diet. Conclusions CRD was associated with reduced HbA1c and weight. Weight loss was associated with HbA1c normalisation; however, no independent statistical relationship was observed between carbohydrate reduction and glycaemic outcomes. HbA1c normalisation often occurred with LCD, suggesting it is a viable option for individualised care alongside other dietary approaches in T2D.