Low-Carbohydrate Diet Trial in Type 2 Diabetes Reports HbA1c and Weight Changes

Key Takeaways

• Lower HbA1c and body weight were observed over 6 months in this free-living cohort.
• Weight loss was associated with HbA1c normalization, although no linear association was observed between weight change and HbA1c change. Carbohydrate reduction was not associated with HbA1c change or HbA1c normalization in regression analyses.
• Motivation and empowerment supported adherence, with health improvement and reduced medication as key motivators, while social and household factors complicated adherence, and the single-arm design limits causal interpretation.

The prospective observational mixed-methods study followed 48 adults recruited from general practitioner surgeries in the Guildford, Surrey, area and also recorded a decline in body weight. Follow-up combined quantitative outcomes with participant experience data in a single-arm outpatient programme conducted under routine living conditions rather than a controlled comparison.

Participants had HbA1c at least 6.5% (48 mmol/mol), mean age 67±10 years, 55% were male, and 15 also contributed qualitative data. The eight-session carbohydrate-reduced diet coaching programme was delivered by The Lifestyle Club in a free-living outpatient setting, with study visits at the University of Surrey. Sessions covered diabetes, reduced-carbohydrate eating, shopping, food labels, eating out, and intermittent fasting. Delivery included group sessions, a booklet, expert videos, a WhatsApp group, and optional monthly catch-up or support communities. Participants were advised to reduce carbohydrates without a specific target and could self-manage oral medication and physical activity, keeping the intervention grounded in routine self-management.

Mean carbohydrate intake fell from 226.0±102 g/day to 126.3±78.5 g/day over 6 months, and carbohydrate energy share dropped from 42.6±7.8% to 29.7±9.6%, both p<0.001. Mean body weight decreased by 5.2±4.4 kg, and BMI declined from 30.6±6.5 to 28.8±5.7 kg/m². Daily protein and fat grams did not change significantly, although their energy shares rose as carbohydrates fell. Dietary fibre intake also fell from 17.6±6.2 g to 13.3±5.7 g, with p<0.001. No significant changes were observed in lipids or blood pressure, and these findings remained within-person observations without a comparator arm.

Univariable logistic regression linked greater weight loss with HbA1c normalization, with an odds ratio of 1.413 for each kilogram lost and p=0.002. Linear regression did not show a significant association between weight change and HbA1c change (p=0.111). No relationship emerged between carbohydrate intake change and HbA1c change, and daily carbohydrate reduction did not differ significantly by normalisation status at visit 3, with p=0.065. Baseline HbA1c was lower among participants who later normalized than among those who did not, at 54.8±7.0 versus 64.8±15.2 mmol/mol.

In qualitative interviews, motivation and empowerment supported adherence, while health improvement and reduced medication motivated participation, and social dynamics, domestic routines, older age, and comorbidities hindered maintenance. The authors said the single-arm design, the lack of a comparator, and undocumented exercise or medication use limited causal interpretation in this older cohort.