I think Dr Fung is often misunderstood. He appears on a lot of youtube videos with Low Carb High Fat (LCHF) diet folks. This has led people to believe that he is a backer of LCHF. From what I see he does support LCHF as a safe way of dieting but his actual advice is more nuanced than that.
Dr Fung’s position seems to be that the main point is to get to where your body is burning fat and they way he gets people there is to use Intermittent Fasting. To his way of thinking the type of diet matters much less than the Intermittent Fasting.
That doesn’t mean eat anything you want. He clearly says (How to Reverse Type 2 Diabetes, The Quick Start Guide):
The first step is to eliminate all sugar and refined starches from your diet. Sugar has no nutritional value and can therefore be eliminated. Starches are simply long chains of sugars. Highly refined starches such as flour or white rice are quickly broken down by digestion into glucose.
As long as the diet eliminates simple sugar and refined starches things are good.
Intermittent fasting allows time for the body to move from processing the last meal and into consuming stored fat from the body. Yesterday I did a 20/4 fast. I ate dinner at 5 PM and drank my last beer by 9 PM.