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I like to cook from scratch, and I'm currently trying to loose a few pounds. I know that cooked food is generally more calorific than raw food, so if I add up the calories of the ingredients I know it won't give an accurate result.

So my questions are two-fold:

How much difference is there between a raw food item and a cooked food item?

Is there a method to deduce the calorie content of cooked food (given the know values of its raw form) ?

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Can you please link to a reference? There seems to be a violation of conservation of energy implied here. –  bmargulies Jul 10 '10 at 13:20
    
@bmargulies -- how is it a violation? Cooking = Food + Heat, and Heat = Energy. –  Joe Jul 10 '10 at 14:36
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@Joe Well, I hadn't considered that, but my creaky memories of chemistry lead me to be to be skeptical of the amounts. More likely, cooking some things makes more calories available to the human digestive tract. –  bmargulies Jul 10 '10 at 15:36
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Get out your calorimeter, thermometer, and refresh yourself on enthalpy changes from high-school chemistry. Proceed by totally combusting the food in the calorimeter and measuring temperature change to calculate heat gain... Oh wait, you've just ruined your dinner now. –  Noldorin Aug 5 '10 at 14:00
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Why are so many people on this page talking about the chemical definition of calories? That's not what they're asking. This question is obviously about food-calories -- as in the amount of calories your body absorbs when you eat something, which does change when you cook things because they become easier to digest. –  Brendan Long Jan 19 '11 at 0:41
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6 Answers

I believe the only type of food that gains calories from cooking is starches, and it would vary depending on the type of starch.

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I do not see how this can be true. Calorie is energy and you cannot increase the energy of a something like that. You may just decrease water content hence getting more calorie per grams, but in that case this should apply to everything and not only starches. Can you explain? –  Recep Jul 15 '10 at 10:30
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Some starches start out hard to digest (or even indigestible) and are likely to pass through the body without being fully digested. Cooking breaks these starches down making them more easily digestible. –  BarrettJ Jul 16 '10 at 13:23
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Calories are a measure of energy, so technically warm food has more energy than cold food. It's possible that the way that it's cooked might add fat (saute, frying, etc), which will add to the chemical energy available.

But the real issue is a factor of absorption -- cooking makes more nutrients available that the body wouldn't otherwise be able to use. Do those nutrients have calories? It's possible, I guess, but to get the same nutrients, you'd have to eat more of the raw food.

I really don't know calories are calculated these days -- it used to be a measure of how much energy was given off when the dehydrated food was burned, but with the advent of things like Olestra that are considered '0 calorie' are only so because they can't be absorbed by the body.

I've heard that one of the suspected reasons for the advent of human civilization was because of cooking that might be the source of your question. From the Publisher's Weekly summary of Catching Fire: How Cooking Made Us Human:

By making food more digestible and easier to extract energy from, Wrangham reasons, cooking enabled hominids' jaws, teeth and guts to shrink, freeing up calories to fuel their expanding brains.

... but that doesn't specifically say that it added calories, as it "liberated mankind from the drudgery of chewing", which would've required energy. (sort of like the 'negative calories' of raw celery)

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Warmness has nothing to do with it. The difference is completely negligible -- food calories are actually kilocalories, and warming something up will only increase its energy by a few normal calories. A quick search for "cooking digestion" on Google turns up this site: beyondveg.com/tu-j-l/raw-cooked/raw-cooked-2a.shtml which mostly talks about other things but cites a study showing that cooked starch becomes 2-12x more digestable, meaning 2-12x more calories. –  Brendan Long Jan 19 '11 at 0:46
    
@Brendan : it's negligible? A "Calorie" (ie, kilocalorie) is the energy required to raise 1kg of water 1°C. So 0.5L (about a pint; 80 Calories by nutrition labels) of hot chicken broth at 50°C (about 120°F) would have 20 more Calories more energy in it than at 10°C (50°F), or 25% difference ... I, too, can pick out specific examples to support my argument. The problem is, the way of measuring Calories for nutrition labels (a bomb calorimeter) can't take temperature or digestability into account. Don't blame us, blame the US FDA for thinking they can summarize food as a bunch of numbers. –  Joe Jan 19 '11 at 3:12
    
Temperature = physical energy. The energy of food is a measurement of chemical potential energy. (Sorry I do realize how old this answer is but I thought I'd post anyway). –  Bizorke Dec 19 '11 at 22:55
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This question is impossible to answer.

There are two things going on: the first is that it takes less of your own calories to process cooked foods, of all sorts. This is (I think) always going to be true because the heat applied during cooking breaks down bonds between the food molecules, so your stomach won't have to.

So, eating a raw food will require more net calories of work to process it than eating it's exactly-the-same cooked counterpart. This 'net calories' conversation is one arm of the question.

Where you run into troubles: food has water in it. How are you going measuring your cooked and raw food to compare? One cup of squash that has all the fluid cooked out of it is more calories than one cup of raw squash. One oz of squash that has all the fluid cooked out of it has more calories than one oz of raw squash.

Finally, there's the what-you-cook-it-in factor: cooking something in butter adds available calories, although not as much as the whole butter amount, since some is left in the pan, drips off the sides, etc.

All that said, getting super exact is impossible, sorry!

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It's worth pointing out specifically that, even with this logic, cooking does NOT add calories to food. It may reduce the amount of calories you burn processing it, but there's no net gain. –  bikeboy389 Jan 18 '11 at 15:19
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Here's a quick and dirty table to help you get a rough idea of the calorie content of what you are cooking. Keep in mind that this will only give you an estimation of your meal's calorie count.

--------------------------------------
| Food Component | Calories per gram |
|----------------|-------------------|
|       fat      |         9         |
|     alcohol    |         7         |
|     protein    |         4         |
|  carbohydrates |         4         |
--------------------------------------
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I'm going to risk downvotes and say this:

If you are concerned about the impact of whatever difference in calorie count cooked vs. raw makes, you are cutting it pretty fine. The margin for error is likely very small--probably smaller than your measuring errors, or the inaccuracy of your kitchen (or bathroom) scale.

Keeping an eye on calories is fine for weight loss. Reducing calorie intake and/or increasing calorie burning is the only proven way to do it. But looking out to avoid that 20 calorie margin of error suggests that either you're not cutting enough calories in the first place that 20 matters, or you're tormenting yourself over things you shouldn't be worried about. Cut yourself some slack, and don't sweat the small stuff. The simple act of realistically monitoring how much you eat is more likely to help you than obsessing over every single calorie.

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Your risk taking gained you an upvote :) –  slim Jan 18 '11 at 15:40
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The difference between raw and cooked forms depends on the type of food and how you cook it. Some food takes on water, some release water, some change their chemical composure entirely.

Truth be told the differences are very minor.

To use your example:

*raw*     chicken whole egg contains 151 calories per 100g
*poached* chicken egg has 147 per 100g

This is (relatively) nothing.

Perhaps a little more powerful than you need, but there are web services which can reference USDA maintained databases of thousands of ingredients in cooked and raw form, thus negating the need to deduce anything. I use a la calc (they have a time unlimited free trial) as they provide a UK service but they do have the latest USDA database too.

You could download the USDA nutrition databases yourself from the USDA website but I tried that and, to be frank, it's all gibberish to me. The website I mentioned has a good interface that flashes up the data of every ingredient they have (they claim they have 12,000+).

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