Meat, chicken, fish, eggs, dried legumes and nuts are in the same food group, but the amount of protein in one standard portion of each is not the same. Türkiye Beslenme Rehberi (TÜBER), Türkiye's national dietary guideline, gives the ratio plainly: one standard portion of cooked dried legumes contains half the protein of one standard portion of red meat and chicken, and one third the protein of one standard portion of fish.
Why are the portions not equal?
The reason is which measure the equivalence is built on. The guideline keeps within-group equivalence on the basis of the energy content of the foods. The protein content of two portions equalized by energy is not necessarily equalized too; the guideline notes separately that this should not be forgotten.
This does not mean that dried legumes are a weak source. The same portion carries carbohydrate, fiber, oligosaccharides and phytochemicals as well; the comparison is being made over a single line only, the protein line. Because the energy value of the same portion is held equal, the difference on the protein side is in fact a result of the difference in composition.
Where does the egg stand?
The egg shares the same step with dried legumes in this table: the protein amount of one standard portion of cooked dried legumes is similar to that of one standard portion of egg. The difference between the two is not in the amount but in protein quality. While the egg appears in the guideline as the food with the highest protein quality, the quality of dried legumes is counted as low because of their limitation in sulfur-containing amino acids.
Nuts and oilseeds are at the bottom of the step: one standard portion of them contains one quarter the protein of one standard portion of red meat and chicken. That is why this group is positioned less as a protein source than as a complement that carries fat and minerals alongside. The portion measure is small accordingly: a handful, that is 30 hazelnuts or 4 walnuts.
Two comparisons that come out of the ratios
The ratios the guideline gives can be made to talk to one another. Since dried legumes carry half the protein of red meat and nuts one quarter, one portion of dried legumes contains twice the protein of one portion of nuts.
The second comparison is on the fish side. Since dried legumes carry at the same time half the protein of red meat and one third that of fish, one standard portion of fish contains one and a half times the protein of one standard portion of red meat. These two numbers are not written separately in the guideline; they are derived from the ratios it gives.
The portion count side
The guideline puts a limit on how the group's portion count is filled as well. Filling the oilseed and nut allowance with meat or chicken is not recommended; these items should be eaten in the stated amount, so that a total of 3.5 standard portions a week is completed.
For dried legumes a different route of equivalence is defined. A dish of dried legumes can be eaten in place of bread and grains; in that case carbohydrate equivalence is taken as the basis, and one standard portion of a dried legume dish counts as one standard portion of bread or grain.
What does the group carry together?
What this group shares is not only protein. While gathering meat, chicken, fish, eggs, dried legumes, oilseeds and nuts under the same heading, the guideline states that all of them are a source of iron, zinc, phosphorus and magnesium, and of vitamins B1, B6, B12 and A.
Two items are particular to the group. Vitamin B12 is found only in animal-based foods; dried legumes, meanwhile, are also a good fiber source. So when a portion exchange is made, these two lines move alongside the protein line.
In nuts and oilseeds there is an additional measure: because these items contain more fat than other foods, attention is asked to be paid to the amounts consumed. Their protein contribution being low and their energy contribution high comes from the same reason.
Where does it turn into a mistake?
The first mistake is taking within-group equivalence for protein equality and replacing meat entirely with dried legumes; the portion count holds, the protein total does not. The second mistake is counting nuts as a main protein source.
The third mistake is not reading the ratio apart from quality: the amount ratio and the amino acid pattern are two separate measures. The fourth mistake is taking within-group exchange to be limited to the portion count. The guideline opens a second route for dried legumes and ties them to the bread and grain group over carbohydrate; that is, the same dish can be written into the account of two different groups, but not into both at once.
For the quality side you can look at the protein quality article, and for the calculation of the daily total at the protein guide.