I'm studying amino acids content in vegetable food. I was looking at peanut protein and noticed its similarity with chicken meat, as you can see in the table below (quantities are measured in grams). Third column is first column minus second column. Green amino acids are the essential ones.

The biggest difference (-1.11) happens for Lysine, but Lysine quantity (0.901) is still bigger than the lowest one, which is Tryptophan (0.2445). So in this case, is Tryptophan the limiting factor in protein synthesis? (Tryptophan amount is < than any other amount).

enter image description here

The table below lists the optimal profile of the essential amino acids (first column). Second column is obtained by dividing the values in table 1, first column, by 25.3055 and multiplying by 1000.

Notice that Lysine is the only one amino acid less than the reference (36<51).

enter image description here

So the questions are:

1) Have peanut proteins a limiting factor (if yes what is and why?) or can be considered a complete protein?

2) If the answer to 1) is "yes it has a limiting factor" what vegetable foods rich in lysine can be eaten with peanut in order to obtain all the amino acids? And how to calculate the ratio of peanut and the complementary foods to eat in order to get the proper profile of the essential amino acids?

Source for first table (first and second columns) https://ndb.nal.usda.gov

Source for second table (first column) http://nutritiondata.self.com/help/analysis-help

I'm not sure if biology is the correct site to post this question, so if you know a better one let me know, thanks.


2 Answers 2


I posted an answer to a similar question here: https://health.stackexchange.com/questions/9124/is-all-protein-the-same/9130#9130

You're not using protein as it is to maintain your body. It's first broken down to the individual amino acids, which your body can then use to build new stuff.

If you're lacking one of the essential amino acids, you can only build as much new protein until that runs out, and all the other amino acids are just excess. A protein that contains all the necessary amino acids is called a complete protein, and you could calculate the differences in the so-called quality of the protein.

A perfect protein (i.e. from egg/milk/soy) will contain amino acids in exactly the ratio you need, some protein contains so little of a certain amino acid that you'd need to eat twice as much of that protein (for example rice or peanuts).

In your case, if beef is making you recover fastest, you'd need to eat 30*0.92/0.70 = 39g of peas for the same effect.

You could get around this by combining different sources of protein. For example grains are limited in lysine, while beans are limited in cysteine/methionine.

  • $\begingroup$ thanks for the answer, but could you explain the calculus 30*0.92/0.70 ? $\endgroup$
    – sound wave
    Jan 17, 2018 at 20:49
  • $\begingroup$ It's from this link: en.wikipedia.org/wiki/…. The questioner wanted to know how much pea-protein they needed to eat to get the equivalent of 30g of beef protein. Beef has a "quality factor" of 0.92, pea has 0.70. $\endgroup$
    – VonBeche
    Jan 18, 2018 at 8:51
  • $\begingroup$ Mm I don't know then if that calculus is correct. If you eat 30g of soy protein you get all the essential amino acids. To have the same result with beef you have to eat 30/0.92=32.6g of beef protein, and with pea you have to eat 30/0.7=42.9g of pea protein. This is what I understood from reading about PDCAAS. $\endgroup$
    – sound wave
    Jan 18, 2018 at 21:48
  • $\begingroup$ You're correct, but the poster was talking about the consumption of 30g beef protein. $\endgroup$
    – VonBeche
    Jan 22, 2018 at 13:37
  • $\begingroup$ Ah I understand now $\endgroup$
    – sound wave
    Jan 23, 2018 at 20:19

Firstly, here are many types of proteins in both peanuts and chicken, so it is a little ambiguous to say "peanut proteins" or "chicken proteins". Secondly, proteins are proteins. "Complete" and "incomplete" are simply nonsensical terms for describing these macromolecules. Each protein performs a certain task, be it structural, like keratin, or functional, like enzymes. The purposes, as well as the abundances and characteristics of the proteins in say, a piece of chicken define its traits. The amino acid content, though related to these things about proteins, do not imply them. Proteins in different food items are simply made up differently.

To answer the question, no, there is no inert limiting factor on the synthesis of proteins in peanuts, and yes, these proteins are "complete".

I hope this helps!

  • $\begingroup$ I think sound wave is talking about nutrition, and the use of protein as a food. In nutrition, the terms complete and incomplete protein are widely used. $\endgroup$
    – VonBeche
    Jan 17, 2018 at 16:54
  • $\begingroup$ Ah ok I was unaware of that $\endgroup$ Jan 17, 2018 at 16:56

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