I suspect the real problem with all diets from weight watchers to vegans is ultimately the same.
No two people thrive on the same diet. Each person needs different things.
Classic example. I know someone who eats toast for breakfast sandwiches for lunch and beans on toast for tea, but he's thin as a rake. So clearly the current avoid bread mania doesn't apply to him.
You have to find your own way.
Maybe he has a protein and/or deficiency. Thin as a rake does not mean healthy.
That's my point though. I don't think there's such a thing as a diet that's good for everyone and there's no way of knowing what's healthy anyway, not just by looking at someone.
I suspect when you and I eat the same salad the chemical reaction inside our bodies is more different than it is similar.
It may be good for you and bad for me. And over a population those variations are so great there's no way of designing a universally healthy diet.
I remember reading about the Vietnamese who ate 'healthy' American food during the war. It went very badly.
