One can't, in spite of the initial reported success of following a 600 kcal vegetarian diet for 8 weeks cured all 11 participants of their diabetes, resulting in an enormous very beneficial weight loss of 15 kg and reversal of pancreatic fat infiltration that many think is the underlying defect causing type 2 diabetes, see this 2011 paper Reversal of type 2 diabetes: normalisation of beta cell function in association with decreased pancreas and liver triacylglycerol only just 3 months afterwards diabetes had recurred in 5 out of the 11 see Diet reverses Type 2 Diabetes
The reason they need it: Their own insulin-producing islet cells, located in the pancreas, aren’t working. Now, scientists across the US are racing to develop effective ways to transplant new islet cells in people with diabetes—an alternative that could make daily life easier and lower risk for insulin side effects like dangerous low blood sugar episodes. 
Trick (most important): Go for longer periods of time without eating (yes, yes, fasting). Consume water only for days or weeks at a time. Your fat will literally dissolve away, and with it your type 2 diabetes and other ailments. The definitive book here is Dr. Joel Fuhrman’s book, Fasting and Eating for Health: A Medical Doctor’s Program for Conquering Disease. I highly recommend it; if you’re skeptical, read the 200+ testimonial comments on Amazon. I and at least 20 of my friends have tried fasts lasting days to weeks. It works, and it is amazing.

The aptly named bitter melon is thought to help cells use glucose more effectively and block sugar absorption in the intestine. When Philippine researchers had men and women take bitter melon in capsule form for three months, they had slight, but consistently, lower blood sugar than those taking a placebo. Gastrointestinal problems are possible side effects. You can reverse diabetes with these science-backed strategies.
Although a defect in mitochondrial function is associated with extremes of insulin resistance in skeletal muscle (30), this does not appear to be relevant to the etiology of type 2 diabetes. No defect is present in early type 2 diabetes but rather is directly related to ambient plasma glucose concentration (31). Observed rates of mitochondrial ATP production can be modified by increasing or decreasing plasma fatty acid concentration (32,33). Additionally, the onset of insulin stimulation of mitochondrial ATP synthesis is slow, gradually increasing over 2 h, and quite distinct from the acute onset of insulin’s metabolic effects (34). Although it remains possible that secondary mitochondrial effects of hyperglycemia and excess fatty acids exist, there is no evidence for a primary mitochondrial defect underlying type 2 diabetes.
A good multiple vitamin and mineral product (or “multiple,” for short) is a great way to start supporting nutrient intake in all diabetic patients. This ensures every day that the body receives all the key nutrients it needs so that all its biochemical, hormonal, nutritional, detoxifying, healing, rebuilding, protecting, and strengthening processes can be performed easily and smoothly. The body runs on enzymes, as enzymes speed up reactions to make the body function more efficiently; all enzymes require nutrient cofactors to enable them to effectively engage the action they are designed to do. A good multiple vitamin supplement for diabetes ensures all those cofactors are available every minute, every day.
Trick (important): Cut down on sweets, and if you can, cut them out entirely for a couple months. I still eat ice cream about once a week, and know people who are losing weight on this diet while eating ice cream almost every day. But this probably won’t be the case for everyone. Better to severely restrict sweets for the first few months, and then gradually reintroduce.