The duration of the intervention ranged from 1 week to 2 years.

The carbohydrate-restricted diets (up to 45% of calories from carbohydrates) had the following effects, compared with the higher-carbohydrate diets:

Increased the time spent in the appropriate blood glucose range by approximately 4% (9 studies; moderate certainty)
Decreased daily insulin needs (13 studies; low certainty)

However, HbA1c did not differ between the lower and higher carbohydrate diets.

The high-fiber diets (at least 50 grams of fiber per day) reduced HbA1c by 0.46%, compared to lower-fiber diets (less than 30 grams of fiber per day; 5 studies; moderate certainty).

The following diets did not affect glycemic control: low glycemic index (6 studies), high protein (5 studies), Mediterranean (3 studies), vegan (1 study), and the 5:2 diet (1 study).

The effects of different diets in participants with type 1 diabetes Original paper