how are we able to calculate the calories in food?
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[How they Actually Count the Calories](https://youtu.be/UuN5HXctmYk?si=NGcW-izuLgO9C0VP) — great Howtown video on it.
Despite the answers about bomb calorimeters… pretty much *no one is determining caloric content this way* in practice. That is the scientific way to see how much heat energy something can provide, but that’s not what we actually do with foods.
Studies establish a rough calorie-to-gram ratio for protein, fat and carbohydrates. This isn’t how much energy you can burn out of the food: it’s how much a human being can actually digest out of food. It’s not suuuuper accurate and we know that (it’s close, most of the time… it’s famously not-very-close with nuts, perhaps 20% off), but it’s easy. E.g. 9 calories per gram of fat. Are you using some new, exotic pressed oil? Is it pure oil? Ok: 9 grams of fat. They won’t check if it’s actually 8 or 10 for that exact oil. They’ll just call it 9 and move on.
So if you make a new food product, to determine the calories in it we just look at your ingredients. Every one of those ingredients have probably been analyzed before and is in the books already (the USDA maintains reference lists of this stuff). You’d just add them up in the proportion you’re using in your recipe. Even the nutrition info in those reference lists is usually calculated for that ingredient, not analyzed for it.
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