A systematic review of 22 longitudinal studies (6 cohort studies, 16 clinical trials; n=3,284 adults with type 1 diabetes) evaluated the effects of low-carbohydrate diets (<26% calories from carbs or <130 g/day) and Mediterranean diets on HbA1c and/or time in range (TIR), with a search updated through February 2026.
Low-carbohydrate diets were consistently associated with better glycemic management compared to usual diets or baseline; Mediterranean diets showed less clear benefit and generally appeared less effective than low-carbohydrate diets. CGM-based studies were largely underpowered.
- Small sample sizes and short study durations across included trials limit generalizability. - Narrative synthesis only; no meta-analysis was performed. - CGM-based studies were underpowered, limiting conclusions about time in range.
Low-carbohydrate diets appear to be a promising option for improving glycemic control in type 1 diabetes, and clinicians may consider discussing this approach with motivated patients. However, evidence quality is low, and longer, better-powered trials are needed before strong dietary recommendations can be made.
