I frankly have no clue what would happen to a diabetic if they fasted.
The Type II diabetic that fasts is just like you and me.
When they don't have the calorie intake their body uses fat as its energy source. There are organs in the body though that can not use fat as a fuel and can only use glucose (brain cells, red blood corpuscles, kidneys) and so the body also manufactures glucose from other materials in the body. Glucose is made from the glycerol "backbone" that is a component of fats (triacylglyceride) and the three fatty acids (where the tri comes in) are used as fuel by muscle cells etc. The other way the body makes glucose is by breaking down muscle and other proteins and converting certain amino acids into glucose.
The Type II diabetic does all of this just the same as anyone else. Usually they are a Type II diabetic because they are overweight and their body has become insensitive to insulin. The fasting is what they need to do a whole lot more of and also eating food that has a much lower glycemic index to stop big sugar spikes in their blood. As in the video, when they start controlling their diet their body will usually become sensitive to insulin again and they will no longer be a Type II diabetic.
The Type I diabetic can not be cured by diet. As in the video they will need less insulin but that is only because they are eating less food. The Type I diabetic could only do that for a given length of time until they died because they still need a certain number of calories a day to survive and will still always need insulin injections to stay alive. Type I diabetes used to be a death sentence. The curse of Adam.
Almost EVERYTHING is curable with God-given herbs, vitamins, diet, and exercise.
It certainly helps to look after one's heath as much as possible with God-given herbs, vitamins, diet, and exercise but also important to be caring of those who have clinical chemical pathological disorders of which there are many and no amount of what the person does will enable them to overcome those problems. e.g. Type I diabetes, Glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency) etc etc.
There are however no metabolic disorders that cause a person to be overweight due to fat storage (overweight due to fluid retention not included).