Okay so this assumes that calories are basically energy from respiration, if im wrong please correct me as well, i know that a calorie is considered the energy to heat up 1g of water i think or something, but generally its energy , and the body currency of energy is ATP which is mainly from respiration right, so amino acids from protein are usually not used in respiration unless taken beyond a limit, but that isn’t taken into account when calculating its calories, every 1g of protein gives off 4 calories same amount as carbs, which is the main source of fuel for respiration lol, is there something i misunderstood about calorie concepts?
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Calories are a measure of energy, that’s it. You can use it to describe the quantity of energy the sun emits, the quantity of energy in food, the quantity of energy in a litre of fuel if you burn it.
As for how the body generates energy, it has multiple mechanisms. It can convert sugars to energy, it can convert fats to energy, and it can convert amino acids to energy.
What gets allocated to what depends on the body’s needs, and what’s available to it. If you need energy right away and you’re exercising, sugar is the way to go. You can get energy from it fast. If you need energy after exercising, fats are a great way to get it. You don’t need lots of energy in a short amount of time after all. If you’ve got a bunch of protein available, you don’t need them for building your own proteins after breaking them down, then it’s a good source of energy just lying there.
Those mechanisms also allow you to cannibalize your own body in case of starvation. It’s a great survival mechanism since it gives you more time to find sources of food.
EDIT: adding reference https://www.nature.com/scitable/topicpage/nutrient-utilization-in-humans-metabolism-pathways-14234029/ (dense reading ahead).
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