@Jabe73 If these were scientifically proven effective, I believe doctors would use these methods. It’s pretty well accepted that a calorie restriction diet seems to offer longer life, less disease. I would argue that maybe part of the reason is not simply that it is lower calorie, part of the mechanism might be something to do with sugar levels, how the body uses, eliminates and stores calories, which might relate to the information you have read regarding lower carbs.
Also, most medical doctors would agree a vegan diet is healthier with the studies that have been done. Recommendations by our government are to try and be realistic with small modifications to a typical American diet, no one really thinks it is ideal for health I think, just reasonable.
Low carb or no carb, like an Atkins diet in my opinion was a horrible diet craze in America, because the average person thought it license to eat bacon and cheese hamburgers with no bun all of the time. Almost everyone I know who did Atkins, or how they interpreted Atkins, who bothed to get blood tests had very elevated cholesterol. Heart diseases usually gets people younger than cancer. So, we have to be careful about general diet recommendations to the public at large.
Now, I am assuming you are talking about low carb diet regarding once already diagnosed? I would say most Americans are too out of control with how they eat to follow a diet so different for long periods of time. Most Americans want a magic pill.