We're talking about a quick 100 here, not a nice day in the country where even I would prefer a good pub lunch over any power bar.
100 miles, 4-5 hours, easy +5000 calories. Even if you start fully carbo loaded and after a light breakfast you're still looking at replacing +2500 calories during the ride. That's 25 bananas, are you going to carry 25 bananas in your jersey pocket? Or maybe you think a few pork pies will do the job, you may only need about 8 of them. (And do you consider a pork pie more of a real food than say a Clif bar?)
Real food doesn't cut it because you often have to eat bigger helpings to extract the nutrients required, which means the gut has to work harder (not great when you're trying to ride at 20mph) and you have to carry more food.
What food then, can be carried to fuel a fast 100miler?