I am short for time now so I can’t get into everything, but I will give it a start. First of all, you are talking about type 2 diabetes. Type 1 can’t be cured, though some people with type 1 also develop insulin resistance and end up with “double diabetes.”
My son has type 1 diabetes. I also have been able to talk with dozens of type 1 diabetics over the years who use different dietary strategies ranging from ketogenic to 80/10/10 (80% carbs).
The reason that my experience with type 1 diabetics is important is because type 1 diabetics know exactly how much insulin is required to maintain normal blood sugar and to manage certain amounts of different types of foods, so we can see which dietary strategies require the most insulin on a daily basis, as well as the most insulin per unit of carbohydrates.
My son currently eats about 25% carbs and 60-65% fat. His blood sugar management is considered to be super-optimal for type 1 diabetes (his A1C is under 6.0). He DOES however use a lot of insulin per gram of carbs. He briefly tried the 80/10/10 diet and the amount of insulin he needed per gram of carbs dropped considerably, but because his total carb intake rose, he needed more daily insulin.
When you eat a high fat, low carb diet (<35% carbs) we know that muscles load up with fatty acids and make enzymes to burn fatty acids, and they do not load up much with glycogen and do not burn glucose as readily. This is established in sports medicine. At a walking pace, for example, someone on a 30% carb diet will burn 75-80% fat while someone on a high carb diet will burn 65-70% fat.
When muscles become fat loaded on a high fat diet, they resist insulin’s effect of moving glucose into the muscle. This is because they are full of fatty acids, and because they do not burn glucose off as fast for energy. Type 1 diabetics for example who eat high carbs tend to need about 1 unit of insulin for about 20 grams of carbs, while type 1 diabetics who eat less than 35% carbs tend to need about 1 unit per 6-10 grams of carbs. This includes ketogenic dieters. Low carb dieters without diabetes who attempt a glucose challenge will often fail because their muscles are fat loaded, and a glucose tolerance test is considered to be invalid unless the person testing has consumed at least 150 grams of carbs for each of the last 3 days.
As a result of fat loading on ketogenic, and “low/moderate 20-35%” carb diets, more insulin is required to manage a certain amount of carbs and YES muscles could be described as being insulin resistant. On the other hand, high fat diets do not worsen blood lipid profiles. Triglycerides correlate primarily to sucrose and alcohol intake. Carbs, and primarily fructose is turned into triglycerides (not dietary fat).
We also know that the muscular insulin resistance on a high fat diet is due to fat loading because it takes several days to arise. A single high fat meal does not suddenly radically raise insulin requirements but 4-7 days of low carb, high fat will gradually cause in increase in insulin required per unit of carbs.
So point number 1 is that insulin output is not that closely related to CARB intake but to total calorie intake, If you are overeating, you will need more insulin. A low carb diet will require less insuln because there are fewer carbs, but more insulin because the muscles will be fat loaded and less sensitive to insulin’s effect of moving glucose into muscles. In my son’s case, he tripled his carb intake during a 2 week “experiment” but he only needed about 130% as much insulin because he needed far less per gram of carbs after 2-3 days. This effect also took time to manifest itself.
SO, the way to reduce daily insulin levels is not to reduce carbs, nor fat, but to eat a maintenance to below maintenance level amount of calories, however we still know that the liver becomes progressively insulin resistant when fructose and alcohol intake is high.
Part of the issue seems to be that there are different mechanisms of type 2 diabetes. Some people have primarily liver insulin resistance due to fat deposits. Some are insulin resistant because they have excess adipose. Some are insulin resistant because their insulin receptors are flawed and so they have to pump out a lot of insulin to get glucose into the liver and into muscles. I have to think about this some more, but in general I would say that if you have liver insulin resistance/high triglycerides, you should not use a high carb diet. A high fat diet (with maintenance or fewer) calories will improve liver insulin sensitivity. If you are overfat in general, it doesn’t really matter as long as you eat below maintenance calores. If you have an insulin receptor malfunction, a low fat diet may help make muscles more insulin sensitive by clearing out intermuscular fatty acids and creating room for glycogen with less need for insulin. Activity levels may help this too.
How does he know he was cured? He could have normalized blood sugar, but still be very insulin resistant. Weight loss will improve insulin sensitivity, but low fat diets negatively affect hormone levels. Also, carbs that are more inflammatory to the individual will cause insulin resistance by raising cortisol levels. (so you can also develop insulin resistance from high stress/poor sleep due to high levels of stress hormones.).
I think it is important to determine whether type 1 diabetes was due to insulin receptor malfunction, liver insulin resistance, stress hormone levels or general over-fatness. Honestly, I don’t know all the answers, but losing fat, reducing fructose and alcohol, raising activity levels, and reducing stress hormones will always help as well as minimizing high omega 6 oils and inflammatiory foods (which can be very individualistically specific-my son needs a ton more insulin from high gluten wheat for example).
For type 1 diabetics, I have seen people do OK on 80/10/10 diet. They tend to run higher, like 6.5 A1C than my son can achieve on 25% carbs, and there are ketogenic type 1 diabetics who have A1C’s in the 4.2 to 5.0 range, but the advantage is that since less insulin is needed for food, there is less absolute error in insulin dosing. At 25% carbs, my son can run an entire meal period with a blood sugar in the 70-90 range, but there are meals where you guess wrong on carbs or activity levels and spike higher.
The main advantages of lower carbs is not a large reduction in insulin needs, but improved blood sugar and energy stability and less hypoglycemia because a higher fat meal will extend the energy provided from a meal and prevent a blood sugar crash.
Low carb/high fat type 1 diabetics tend to have less hypoglycemia and if they monitor blood sugar closely, they can keep their blood sugar lower more safely because the high fat diet tends to resist sudden crashes because the body used fat more readily under stress rather than blood sugar and glycogen.
I have come to believe that the real dilemma with carbs is that carbs are either low GI/high inflammatory which causes chronic over secretion of insulin due to the inflammatory effects, or they are high GI (fast) and tend to produce an over-release of insulin especially in people who are already insulin resistant, and then result in energy crashes 2-3 hours later. In either case, you end up getting more insulin than you need for your energetic needs. As a result I also have to say that I am pretty convinced that some people will need less insulin on a low carb diet and some will need less on a low fat diet (calories being equal).