Let's say there are two diets, consisting of entirely different proteins. If you split up all of the proteins from one day of each diet, you'll get the same set of amino acids and the same count of each. Assume everything else about the diets is the same.

Would these diets have the same effect on the protein composition in your body? Different polypeptides, but overall the monomers are identical. Does your body break down proteins entirely, or will it reuse some chains of amino acids?

  • $\begingroup$ I'm thinking this question would be better suited to the Biology exchange, but it's not clear to me what "same effect on your nutrition" means and I'm guessing the folks in Biology will have the same problem. Can you clarify that aspect of your question? $\endgroup$ – Carey Gregory Aug 28 '19 at 1:06
  • $\begingroup$ I changed "the effect on nutrition" into "the effect on the protein composition in your body" to make it clear what you are asking. During digestion, proteins are not necessarily broken down into individual amino acids but, to some extent, also into di- and tripeptides or even larger peptides that can be absorbed. This question would better suit in Biology SE or maybe Chemistry SE - they discuss about biochemistry there a lot. $\endgroup$ – Jan Aug 28 '19 at 6:55

Arrangement of amino acids determines the protein structure which in turn can determine how easy it is to digest the protein. I cannot think of an example right now; never really checked if two entirely different proteins have identical composition. However, it is not really surprising. In chemistry, it is known that different isomers have vastly different physical properties.

So if the two proteins have different digestibility then they will have different nutritive values.

Regarding, protein digestion and nutrition. New proteins are built from individual amino acids and not pre-formed oligomers. Read about translation. So at some point the ingested protein has to be completely broken down into amino acids.

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  • $\begingroup$ It's your last sentence that's crucial. It is known that some, even large peptides, can be absorbed, so it's not necessary for a protein to be digested into a single amino acid in the intestine in order to be absorbed into the bloodstream. You are suggesting that all body proteins can be created only from individual amino acids, so any dietary peptides/proteins may need to be broken down at some later point...Translation is about single amino acids, but can some pre-formed (dietary) peptides find the way into body proteins...This would answer a lot of related questions... $\endgroup$ – Jan Sep 10 '19 at 17:47
  • $\begingroup$ @Jan "can some pre-formed (dietary) peptides find the way into body proteins".. Not in my knowledge. $\endgroup$ – WYSIWYG Sep 10 '19 at 20:44

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