So best diet will be a low carb diet, with plenty of protein (protein digests slowly and helps stable blood sugars), healthy fats (also helps slow digestion
and thus less
insulin requirements),
and small amounts of carbs coming from non-sweetened foods / mostly non-starchy veges.
Eliminate added sugars, sweetened and processed foods, and starchy vegetables / fruits. Nuts, unsweetened dairy, vegetables, meats, cheese, etc.