What role does cooking play in digestion?
We put this question to geneticist Giles Yeo.
Giles - Cooking had a very important role in the evolution of humankind because what it did was increase the availability of calories. Now what do I mean by that?
If you assume 100 calories of sugar - thatís 100 calories, okay, because there's no processing required. If you assume 100 calories of celery or 100 calories of sweet corn, then I think you can tell in the loo the next morning after youíve had the sweetcorn, not all the corn is going to get absorbed into you. What cooking does is to actually increase this availability. So, if you take the corn and put it in a stew, you end up for any given mass, any given amount of food is get more calories from it. And this clearly then played a huge role because you put in the effort to pick food, gather food, hunt food and clearly the more you get from that effort, the more likely you are to survive. So, what cooking does is take the same amount of food and allow you to get more calories out of it.
Emma - So does cooking actually make food more digestible?
Giles - Cooking makes certain types of food more digestible by beginning the breaking-down process. Some foods will never be digestible by human beings. Grass is probably a good example. You need a rumen for that, you need specific type of bugs. But yes, cooking does make certain types of food more digestible.
Emma - Which foods would we be unable to digest if we didnít cook them?
Giles - Thatís an interesting question. I think an interesting thing to that is, actually, sweet corn is a very good example. Where, in the kernel form, most of it doesnít get digested. The interesting thing about that is that if you then actually break it down into flour and bake and eat it you can actually digest a lot more of it. So thatís a perfect example where you make cornbread and clearly you donít poop out cornbread the other side. Corn is a very good example where cooking, processing, turning it into cornbread makes it digestible whereas the other is not.
I don't know too much about cooking chemistry, but I'll share some of what I do know, regarding digestibility...
A recent paper suggests that cooking greatly reduces the mechanical strength and elasticity of food, allowing extraction of far more calories.