He can eat wheat berries or rolled wheat/rye/barley. I don't think he eats much of it. He does like multi-grain hot cereal. He can eat corn, not tortillas or chips. He can eat rice, preferably brown, but not rice noodles.
It's probably the acellular carbs and the higher fiber. He gets no carbs without the fiber it came with. He is a binge eater, not thin, but he's pretty active (he was before, too, I met him on the Pacific Crest Trail) so he can keep from total obesity. Looks like a powerlifter. His wife is skinny. You'd never know she lost 130lbs. They are both in their 60s.