Yeah he's posting nonsense. If it were true you'd be passing huge chunks of undigested food and be sick. Very little of the calorie content of oats and other so-called fiber rich food is actually undigestible. Sorry...beating obesity is not as easy as eating cereal and oats all day. wish it were.

Your reading is overly simplistic. You're also feeding a huge diversity of disparate microbes when you eat, all of which produce a huge array of different chemicals during their normal life processes, all within our digestive tract. The question then is the interaction of all these different microbes and chemicals with the food and the human and the other microbes.