We all know that protein is made of amino acids, but have you ever wondered why a Nutrition Facts label on your food says “protein”, even though the amino acids are different?

To keep this post “byte sized”, we focusing only on foods here.

First,

Protein content may be calculated on the basis of the factor 6.25 times the nitrogen content of the food as determined by the appropriate method of analysis as given in the “Official Methods of Analysis of the AOAC International,” except when official AOAC procedures described in this paragraph (c)(7) require a specific factor other than 6.25, that specific factor shall be used.

Also of note, is that only 80% of the material needs to show up. In other words, your 20g of protein may only by 16g, Link Here

Class II nutrients are vitamins, minerals, protein, total carbohydrate, dietary fiber, other carbohydrate, polyunsaturated and monounsaturated fat, or potassium that occur naturally in a food product. Class II nutrients must be present at 80% or more of the value declared on the label. As an example: If vitamin C is a naturally occurring nutrient in a product, and the product declares 10% DV vitamin C (i.e., 6 mg/serving) on its label, then laboratory analysis must find at least 80% of the label value (80% of 6 mg or 4.8 mg vitamin C/serving) for the product to be in compliance.

Also:

(7) “Protein”: A statement of the number of grams of protein in a serving, expressed to the nearest gram, except that if a serving contains less than 1 gram, the statement “Contains less than 1 gram” or “less than 1 gram” may be used as an alternative, and if the serving contains less than 0.5 gram, the content may be expressed as zero. When the protein in foods represented or purported to be for adults and children 4 or more years of age has a protein quality value that is a protein digestibility-corrected amino acid score of less than 20 expressed as a percent, or when the protein in a food represented or purported to be for children greater than 1 but less than 4 years of age has a protein quality value that is a protein digestibility-corrected amino acid score of less than 40 expressed as a percent, either of the following shall be placed adjacent to the declaration of protein content by weight: The statement “not a significant source of protein,” or a listing aligned under the column headed “Percent Daily Value” of the corrected amount of protein per serving, as determined in paragraph (c)(7)(ii) of this section, calculated as a percentage of the Daily Reference Value (DRV) or Reference Daily Intake (RDI), as appropriate, for protein and expressed as a Percent of Daily Value. When the protein quality in a food as measured by the Protein Efficiency Ratio (PER) is less than 40 percent of the reference standard (casein) for a food represented or purported to be specifically for infants through 12 months, the statement “not a significant source of protein” shall be placed adjacent to the declaration of protein content. Protein content may be calculated on the basis of the factor 6.25 times the nitrogen content of the food as determined by the appropriate method of analysis as given in the “Official Methods of Analysis of the AOAC International,” except when official AOAC procedures described in this paragraph (c)(7) require a specific factor other than 6.25, that specific factor shall be used.