Actually, it’s obvious. If diabetics eat less of what is broken down to sugar (carbohydrates) their blood sugar levels improve.
It’s been shown in many studies already and now there’s one more. More details here:
American Diabetes Association: Weight Loss, Glycemic Control, and Cardiovascular Disease Risk Factors in Response to Differential Diet Composition in a Weight Loss Program in Type 2 Diabetes: A Randomized Controlled Trial
Continuing to advise a high-carb diet for diabetics – without updating knowledge – is irresponsible. It seriously hurts sick people.