Is raw food healthier than cooked food?

Chris Smith asked geneticist Giles Yeo, from Cambridge University, to crunch the numbers on this question posted on The Naked Scientist Forum. 

Giles - I think it depends on what you mean by better for you. If you talk about calories, then it is true that cooking increases caloric availability. Briefly, caloric availability is how many calories you’ll get out of the food rather than as compared to how many calories are actually in the food, so 100 calories of sugar is 100 calories of sugar. But if you take 100 calories of sweet corn and you look in the loo the next day, you clearly haven’t absorbed anywhere near to 100 calories of sweet corn.

With regards to cooking: if you ate raw celery, that’s 6 calories pretty much for a medium stick of raw celery, whereas if you cook it, you get 30 calories just by cooking the celery. So, if you are looking to reduce your calorie intake then yes, cooking it you get more calories but if you don’t cook it then you get less. But then cooking also does a lot more: for example it kills parasites and also there are certain minerals and vitamins that are only made available from the food after you cook it.

So, I think the answer is from a pure caloric point of view maybe, but is it necessarily better for you? That depends.

Chris - So the whole argument about how many calories you burn off in your jaw muscles crunching things up, which is another consideration?

[laughter]

Rachel - I’d heard, actually, if you eat celery, you’re using up more calories eating it than you get from your stick of celery, is that really true?

Giles - No, no. It is a myth but it’s 6 calories per stick; it’s just barely a myth.

Chris - Is that 6 calories per stick how much you consume eating the stick or how much you obtain by eating the stick? When I say consume, as in how much you burn off eating the stick. How many calories do you need to munch it up?

Giles - It depends how many calories are in a stick of celery. It’s probably about 6%, broadly speaking, from eating a stick of celery compared to 100% when you eat 100 calories of sugar, for example.