how do we figure out what what food is protein and what is calories etc?
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Your question prompted me to look it up and it is fascinating.
https://www.livescience.com/62808-how-calories-are-calculated.html#:~:text=Related%3A%20Amino%20acids%20to%20zinc%3A%20A%20glossary%20of%20nutrition%20terms&text=To%20use%20this%20tool%2C%20scientists,of%20calories%20in%20the%20product
Calories are a unit of energy, specifically related to how much energy is required to raise the temperature of one ml of water by 1 degree C. Lots of things have calories, if we can digest them and liberate useable energy from them, often in the forms of fats, carbohydrates such as sugars and starches, and proteins.
The amount of calories per gram of protein is about 4, the same is true of carbohydrates, while fat has about 9 calories per gram. Calories in the dietary sense are a property of fats, proteins and carbs.
To determine the amount of protein there is a technique called the kjeldahl method to measure the amount of nitrogen in the food and convert it to protein content; you can also use UV spectroscopy. Protein has about 4 Calories/gram.
Fat can be measured through a Soxhlet extraction or gas chormatography. Fat has 9 Calories/gram.
Carbohydrates are everything that isn’t fat, alcohol, protein, water or ash; carbs have 4 Calories/gram and alcohol has 7.
The other way is to dehydrate the food and then burn it in a bomb calorimeter and measure the heat that is released. 4,184 J of heat = 1 Calorie. You dehydrate the food first since water has 0 Calories.
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