This is just a general overview. Everybody should discuss with their medical provider before making any changes in their life style.
Diabetes is a massive healthcare issue. In the United States about 1 in 10 people are diabetic. This is an increase from 1 in 100 people who were diabetics in the 1950s. What changed from the 1950s is the food. Diabetes affects everything in the body from bones, muscles to heart and kidneys. Most doctors focus on one or a few organs when talking with patients about diabetes, but truly all organs are affected.
Sadly, the medical system does not do enough to help the diabetic patients. Normally, the fasting blood glucose is around 80-90 mg/dl, but in diabetic patients we came to consider acceptable values that are at least 1.5 to 2 times higher. Imagine going to the doctor with your blood pressure twice as high as normal. Everybody will freak out. So why do we tolerate these high blood sugar values? I think there are two issues. Most doctors have no clue about the true damage caused by diabetes and the second issue is that most doctors do not know how to really manage diabetes and achieve normal blood sugars.
Nowadays the most common diabetes is diabetes type 2 which is more than 90% of all diabetes cases. The most common pathway to diabetes type 2 is weight gain. When we eat carbohydrates and proteins our body secretes insulin and insulin helps to store some of the energy as fat. Over time our fat stores become full. The body develops insulin resistance because there is no more place to put all the excess energy. The insulin levels keep increasing to compensate for the insulin resistance. High insulin level by itself is actually detrimental to health (see this paper by DeFronzo). In the end, the organ secreting insulin (pancreas) may get exhausted by years of over secreting insulin and stops making insulin.
So how do we fix diabetes? There are two issues in diabetes type 2: insulin resistance and high blood glucose. To decrease the insulin resistance the obese patients need to lose weight. As long the insulin levels are high it is very hard to lose weight because insulin is a growth hormone. Therefore, the best way to lose weight is to decrease the insulin levels which can be achieved with low carbohydrate diet or fasting or a combination of fasting and low carbohydrate diet. For normalizing blood glucose levels the best is to follow a low carbohydrate diet.
Low carbohydrate diet is not that hard to achieve. Most people like the foods included in this diet: meat, dairy, eggs, leafy vegetables. One doctor who has diabetes type 1 is Dr. Richard Bernstein. He was diagnosed with diabetes type 1 in 1946 at age 12. He has been practicing low carbohydrate diet since the 1970s. Dr Richard Bernstein has an amazing practical and theoretical knowledge in the diabetes field. He is sharing his knowledge on youtube (recommend Dr. Bernstein's Diabetes University) and in his book The Complete Guide to Achieving Normal Blood Sugars. Other resources include: the diet doctor and low carb md podcast. Virta Health published a bunch of papers about low carb diet: https://www.virtahealth.com/research.
Fasting is an even more accepted practice. Most religions have a form of fasting and fasting has been practiced for thousands of years. One of easier form of fasting is time restricted fasting or intermittent fasting, An easy way to start is 16 hours of fasting and 8 hours of food every day. Multiple days of fasting are also possible. It is important to keep in mind that are our bodies are very efficient and for every full day of fasting we might lose as little as half a pound. Jason Fung is one of more recent advocates of fasting with multiple books and videos on the internet. Fasting is not good just for diabetes, but also for health in general. This a good review article from the New England Journal of Medicine about the benefits of fasting: de Cabo and Mattson. NEJM 2019.