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I'm studying protein synthesis to understand how the body use the different amino acids to build proteins.

In particular I would like to learn how to (roughly) calculate the total amount of protein synthesized knowing the amount of amino acids eaten.

I think the easiest case is that of complete protein with PDCAAS value of 1. I guess that in this case the amount of proteins synthesized is equal to the amount of protein previously ingested, isn't it ?

So consider the more complex case of incomplete proteins, i.e. proteins with limiting amino acids.

For example consider raw lupins, 100g contain about 36g of proteins, with these essential amino acids:

  Amino acid   |   g in 100g of lupins
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Tryptophan     |  0.29
Threonine      |  1.33
Isoleucine     |  1.62
Leucine        |  2.74
Lysine         |  1.93
Methionine     |  0.26
Phenylalanine  |  1.44
Valine         |  1.51
Histidine      |  1.03

source: https://ndb.nal.usda.gov

If I eat 100g of it, how to calculate the final amount of proteins that will be synthesized in my body ? (for simplicity don't consider the protein digestibility)

I guess the first step is to find the limiting amino acid(s) of the lupin, but how can I find it/them ?

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    $\begingroup$ Whatever makes you think the amount of protein synthesized is equal to (or even proportional to) the amount of protein ingested? Ever heard of urea? $\endgroup$ – David Jun 1 '18 at 17:26
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I think it's impossible to estimate because of many reasons. 1) Amino acids are used not only to build new proteins in body. They can be used for other processes. 2) There are thousands of different proteins has been synthesized in cells for different purposes. These proteins differ both in number of amino acids and in what exact amino acids are included in exact protein. You have showed table for 100g lupins, for other proteins this table will be with different numbers. 3) It is impossible to estimate the needs of exact body in exact moment in exact components for exact processes. So it is difficult to evaluate the result of how what we eat will be used by body with good precision.

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  • $\begingroup$ Thank you for pointing this out, didn't know about that. So how can all the sport dietitians give nutrition recommendations about protein intake if this cannot be estimated ? $\endgroup$ – sound wave Jun 2 '18 at 14:07
  • $\begingroup$ I am not dietitian. So I express only my opinion. Recommendations is a result of simplification. General recommendations are not precise enough. They don't take into account individuality. Special recommendations are dictated by your purpose and body feedback. For such radical situation as disease, you have symptoms that give signals. For basically healthy state, you don't have good indicators. Some predictions can be made based on practical knowledge. Experienced dietitian can be more effective in predictions in specific situation. But on some level it's always trying and experimenting. $\endgroup$ – margin Jun 2 '18 at 15:40
  • $\begingroup$ I understand, but in the case of a diet for increase muscle tissue, it is obvious that an increased protein intake is needed. As I wrote in the main question, i'm not interested in the precise quantity, but rather in an estimation. In this case (4-5 days a week of training) I guess the body needs everyday more protein than the average to build and maintain the increased muscle tissue. So, in this particular case, is not easier to estimate the protein synthesis? Should I ask in the fitness board? $\endgroup$ – sound wave Jun 2 '18 at 16:45

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