The Economist has a good article with the following quote:
"Another telling experiment, conducted on rats, did not rely on cooking. Rather the experimenters ground up food pellets and then recompacted them to make them softer. Rats fed on the softer pellets weighed 30% more after 26 weeks than those fed the same weight of standard pellets. The difference was because of the lower cost of digestion. Indeed, Dr Wrangham suspects the main cause of the modern epidemic of obesity is not overeating (which the evidence suggests—in America, at least—is a myth) but the rise of processed foods. These are softer, because that is what people prefer."
I've known about the connection between processed foods and obesity, but this is a new twist. Previously, I just assumed that processed foods were bad because of the high fat and sugar content. But this adds another reason to avoid them. You burn fewer calories digesting them, so you gain more weight.
I wonder how long it will be before this knowledge gets widespread. It could easily form the basis of a diet plan that could really, without any tricks, let you lose weight without eating less or exercising. Just find foods you like that require more metabolic resources to digest. I'm not sure exactly what those would be, but I imagine that things with lots of starches, complex carbohydrates, and fiber would top the list. Of course, those things are typically better for you anyway, so the basic advice wouldn't change much. We've always known that 100 calories worth of raw carrots is very different than 100 calories worth of candy.