I think how humans digest food probably breaks out into four or five different subsets. Eating right for your blood type may have been close. Metabolic testing, imho, is even closer. It always surprises me that people like this man have so much success with diets like this, teaching it, sharing it... maybe his success stories are those whose metabolic typing agrees with the diet. I tested as needing high protein, high fat, low carbs, and when I eat like that, my heart rate goes down, my blood pressure rises the little bit needed to not faint as I stand up, and cholesterol goes down. Any time I've ever tried to eat vegetarian, it leaves me weak. I can have almost no fruit, and have found that most vegetables are way too high in starches for me. As long as I stick to animal protein, nuts, and mostly green leafy vegetables, I do really well. I consume almost no grain. The only fruits I tolerate are apples, bananas, and avocados.
I see vegetarian friends live for months/years on foods that would leave me sick and in bed. We are all so different. With the right metabolic picture, a high fruit diet might be perfect for some people.
When white sugar was first introduced, it was kept under lock and key. It was considered the cocaine of the day. When you consider what a little bit of sugar does in the body of someone who is not used to it at all, it's easy to see why.