Eli5 how are calories measured in food
In: 23
They aren’t! At least not much any more
To measure how many kCal a food contains, you have to burn it, and see how much water it can boil off.
Most governments require you to make an estimate on the total calories based on the ingredients.
In either case, it’s extremely variable.
This is why most modern dieticians don’t recommend calorie counting for weight loss; These estimates can vary by as much as 20%
1 calorie is the amount of energy required to raise 1 cubic centimeter of water, which weighs one gram, by 1 degree Celsius.
As someone else already noted, they use published (kilo)calorie values for the ingredients. Those were determined by burning a quantity of the item in a device called a bomb calorimeter, which measures the total energy released.
The Calorie (the capital letter is important) listed on the label is actually a kilocalorie, or 1000 calories. One calorie is, as was noted by the other commenter, the amount of energy it takes to heat a gram of water by one degree Celsius.
American people got bored, so they decided to see how much you should eat in order to not get fat. They then decide to spread this around the world to ensure that people dont get fat.
There are multiple ways with different levels of accuracy.
I don’t think anyone really uses bomb calorimetry directly, b/c that has nothing to do with food calories and how human metabolism works. Eating a charcoal briquette won’t give the energy contained in that charcoal.
Instead, the calorific content can be estimated based on protein, fat, carb & fiber content (see: Atwater factors) of the food in question, since we know roughly how many calories human metabolism can extract from each gram of these types of macronutrients.
For more details, see: https://skeptics.stackexchange.com/questions/10070/can-a-bomb-calorimeter-meaningfully-measure-food-calories
Carbs and protein contain 4 calories per gram; fat contains 9. It is fairly easy to estimate the amount of carbs/fat/protein in any given food item, and then you can just use the math above to calculate the calories.
Basically we know the calorie(available chemical energy) of the macro nutrients, fiber sugars carbohydrates, fats proteins etc.
And then we measure how much of each of those is in an item to sum up the total caloric value. For instance in chemistry you might try to dissolve the fat of something and measure how much the weight difference is, that way you estimate how much fat there was in the item.
These are estimates though and can be quite a bit off.
Latest Answers