Is it true your body makes its own protein??
Tes, it's true. But to be able to do that, the body has to have amino acids (the building blocks needed to build protein) and you get amino acids from food...
So, you ingest protein, your body decomposes it into amino acids and take those amino acids to build the proteins it needs. That's simplified but you get the idea.
Technically this is correct, but then not really. You need to ingest both protein and amino acids for your body to properly repair and build muscle. The "protein" your body builds is really just the fuel for the muscle (not sure of the technical term) and cannot do it without you ingesting both protein and amino acids.
Well, you can build a house if you have the lumber. The body cannot produce it's own "lumber" or building material. The body will use digested protein, broke down into amino acids or existing muscle for it's many purposes. It cannot not actually produce amino acids form another substance.
Glucose can be produced through gluconeogenesis and used or stored in the muscle or liver, other excess substrates can be converted to fats and stored but protein must come from eating or already "stored" protien (your valuable, existing muscle tissue).
Yeah, that's if youre a carnivore. How do the gravers and those tasty vegetarians do it? (I mean herbivores...)
Well, ingesting protein is just as ingesting amino acids. I don't know if there are foods that contain amino acid not in the form of protein, apart from the supplements. And protein has many functions apart from being "fuel" for the muscle.
Several aminoacids have their origin in the Krebs-cycle and glycolysis. The Krebs-cycle gets its "lumber" from all macronutrients.
Protein is not only used to build muscles. It can be found in any living thing because it has functionnal properties (ie : enzymes that help biochemical reactions) along with structural functions (like being a muscle).
Your body makes non-essential amino acids on its own whether you eat more protein or not. Essential amino acids are needed in the daily diet. That means, yes, your body does make its own protein. It also means, no, this does not mean you don't need to eat any protein at all.
Ummmm, plants like beans and peas, nuts, soy etc. all contain amino acids (protein) along with many more. These foods have to be combined (usually) because thier amino acid profile is incomplete. Animals are not the only source of protein (just the best ones). And when you do not take in enough protein, your body will cannibalize you own muscle for it's needs (hormone production etc.)