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View submission: Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology
Biology:
Most of what ive read about metabolism and nutrition talks about how carbohydrates and fats are digested to create energy. What is the role of protein in providing energy for us? If only a small portion is used to power us, and eating protein without stressing your muscles doesn't really build muscle, what happens to the rest of the protein we eat?
Comment by Indemnity4 at 17/03/2023 at 04:07 UTC*
2 upvotes, 1 direct replies
what happens to the rest of the protein we eat?
It goes down the toilet. Ever notice you take a big dump the day after a feast?
Depending on the type of protein, maybe >90% doesn't get used by your body.
One of the most digestable proteins is casein from cow milk, and that is only about 8% usable.
You chew the food, it passes into your stomach where is starts to break apart into smaller peptides - it's still quite big. But that takes time so a large amount of time so your stomach does feel very full.
Then it moves into your small intestive where enzymes chop it up smaller into amino acids. To move into your bloodsteam requires energy from your body called ATP, so it if isn't needed, your body won't do the work and it keeps on passing through you.
Amino acids that do pass in the bloodsteam have to go to the liver to be processed. Your body then puts them into the general pool of amino acids available to build new muscle or storage as fat. However, again, if your body doesn't need more amino acids, it passes it along and you pee it out.
What is the role of protein in providing energy for us?
Main use is growing new or repairing damaged proteins in your body.
A secondary use is making some signalling molecules, hormones and enzymes in your body.
To be used as energy, your body needs to be deficient in glucose or ATP. It takes energy upfront to convert amino acids into a usable form of fuel. The pay-off is not worth it if any other source of energy exists.
In order to use amino acids to make ATP, glucose, or fat, the nitrogen first has to be removed in a process called deamination, which occurs in the liver and kidneys. The nitrogen is initially released as ammonia, and because ammonia is toxic, the liver transforms it into urea. Urea is then transported to the kidneys and excreted in the urine. If you ever have a simple urine test, one marker is always urea. High urea indicates you have health issues.