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 of energy. Today it is defined as exactly 4.184 joules. The calories used for food energy are more exactly kilocalories so 1000 calories or 4183 joules. Heating up water is the original definition but is no longer used.
Proteins are needed to build all types of cells and other types of tissue not just muscles. Hair for example is primarily made up of protines of the keratin type.
We use proteins both to build up cells but also as a source of energy. To what degree you use proteins as energy depends on your diet. If you eat very little carbohydrate you need to use another energy source like proteins, fat.
If we stars we can use our own tissue as a source of energy. We use fat first, one of the functions of fat in the body is energy storage.
If we need to we can break down muscle and other tissue. Breaking down muscles is not good for you but better than the alternative of just dying.
The ability to break down proteins for energy is very advationous for all animals. Even if you just eat plants you eat a lot of proteins because all living cells contain it. Regular grass is 16-28% protein. That is the percentage of dry weight. Gras is around 83% of water so it is 2-5% protein wet weight
We are omnivores and can survive just by eating animals. It will be hard to get all you need like Vitamin C but it is possible if you need all of the animals and atleas part faw. Inuites have traidtialy a mostly meat-based diet. Whale skin is a source of Vitamine-C so it raw fish.
Just eating meat does not mean you just eat fat and proteins, there is carbohydrate in meat too.
So there is an obvious advantage to being able to use protein for energy.
The idea that we just used carbohydrates, fat, and proteins for energy is a bit of a simplification. we can extract energy from alcohol, organic acids, and other stuff too https://en.wikipedia.org/wiki/Food_energy
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