I know that some types of cooking food can certainly change the nutritional content of the food. Boiling vegetables causes them to lose their vitamins, frying foods can add fat. But what about cases where all you basically did was heat up the food?
Here are a couple of examples:
a) Someone who for dietary reasons had to limit their fiber intake was told they were allowed toast, but not the bread before it was toasted. How does toasting bread remove the fiber?
b) I have heard that popcorn popped with no oil or butter is a great low calorie snack, but corn from lets say a can, even packed only in water, is relatively high calorie. How can popping the kernels remove caloric value?
I am not a nutritionist but here’s a piece of anedotal evidence to give a sense of what might be happening.
IIRC if you eat a potato raw you will actually lose weight. The complex starches in a potato are such that, before cooking, your body would actually have to expend more energy breaking them down than it will ever get back from the food. Cooking the potato does a lot of that work for your body up front. Heating up the potato causes the starchy parts to start breaking down. When you eat it cooked your body now has less work to do to digest the food and will get a net gain in calories from its consumption.
Perhaps similar things are happening on other foods. While nothing may have left the food certain aspects of it are changed by the cooking allowing your body to achieve different results when its digested.
Long ago, I posed this question to my late grandfather, who was a USDA researcher in just this sort of question (well, as long as it was related to meat). I’ll relay his description of cooking a steak. Cooking is essentially a depolymerization chemical reaction. The long muscle strands break down into smaller polymer chains (I suppose that’s some sort of protein chain but I dunno bout that stuff, I dropped out of biochem class). Cooking is primarily a way to make the meat less tough, and also makes the nutrient content more easily digestible. So if you ate a raw slab of steak, it would be extremely tough to digest and would probably pass through you without much absorption of nutrients from the food. So cooking might make the nutrients more easily accessible to the body. Perhaps you might get more nutritive value out of a cooked steak as opposed to uncooked.
However, the overall nutrient value of the steak itself is relatively unaffected by the cooking. Yes, some fat and juices cook off. But the overall nutritional content of the muscle tissue itself is relatively unaffected, the tissue is broken down slightly but not essentially different in quantity of nutrients. Of course this doesn’t apply if you like your steak extra well done and burnt to a cinder. Carbon is indigestible.
Of course, I’m not an expert in this stuff, I’m just relaying an old story my Grampa told me. And I admit he liked to tell a few tall tales. This doesn’t seem to be one of em, but I never heard anyone else describe cooking in this manner.
Calorie guides I have used in dieting say that toast has the same calorie content as the untoasted bread. Cooking adds or removes no calories. Dunno if it changes the fiber content. I’d figure the reverse, toast should be higher in fiber than the raw bread. But I’m only guessing.
Corn is not the same as Popcorn, they are quite distinctly different types of plants.
I’m not seeing how toasted bread would have a different nutritional content from regular bread. All you are doing is heating the toast up to a certain point where the outside changes color, and that’s about it.
The dough has already been baked and changed from its raw form into an edible form. I would think that raw dough would be quite different nutritionally from baked bread. The proteins and the glutens all get changed quite a bit in baking.
–“Corn is not the same as Popcorn, they are quite distinctly different types of plants.”
As I recall, Popcorn IS made from corn. As a matter of fact my aunt makes her own. It IS true that Reddinbacher (sp?) spent some time cross breeding corn in a attempt to get bigger popcorn, but most of his success was achieved in perfecting the drying process.