Why such extremes and few in betweens? Why agave nectar and fruit sugar and not sugar cane? Why wholegrain?

all these diets that are promoted are a way of taking money for old rope as the saying goes .ages ago there were diet breads on the market and all it was,was a loaf half the size of An normal one. i bet all the diets are probably the same kind of thing.remember there were no fat prisoners in the death camps