A lot of research has documented the antidiabetic effects of garlic.
In a 4-week study on type 2 diabetics, garlic powder tablets reduced fasting blood sugar, blood fats, and lowered fructosamine (similar to HbA1c).71
In a 24-week study on type 2 diabetics, garlic tablets significantly lowered blood sugar and cholesterol, and increased HDL cholesterol, compared to placebo tablets.72
Another 12-week study found that garlic tablets reduced fasting blood sugar, HbA1c, inflammation, cholesterol and blood fats, and increased carbohydrate tolerance, in type 2 diabetics.73
Even though garlic tablets were used, raw garlic is probably antidiabetic as well.