Why do the same foods have different protein content on their labels?

In 2022, an enterprising woman named Elena Nacarino filed a lawsuit against Kashi brand foods (and who wouldn’t!). Her claim? That Kashi advertised on the box of one of its cereals that it contained “11g of protein.” The issue? Those 11 grams of protein were not actually digestible as 11 full grams of all the amino acids we need; the amino acid profiles of grains are skewed, meaning the true protein content of the cereal was lower than the packaging claimed. How can this happen? How much protein does any food really have? Where does justice truly lie? And how many grams of protein are actually in Kashi cereal?

There are two ways to measure the number of grams of protein in foods. One is to measure the total grams of amino acid content. The other way is to measure its total nitrogen content. The second method is a less-direct measure, so if manufacturers use the second method, the FDA notes that manufacturers can then calculate a “corrected” protein value using the “protein digestibility corrected amino acid score,” or PDCAAS, and use that number to find a “Percent Daily Value” of the protein in its nutrition label.

We won’t get all the way into this here, but not all amino acids are created equal (if you want that, my piece Collagen sits on a throne of lies goes there). There are many different kinds, and we only need a certain number from food. And to the point of the Kashi case, we need them in the right proportions to be used in our bodies. Foods that have all of the amino acids in the right proportion to each other to all be used up with nothing left over are often referred to as “complete” proteins. Proteins that only have some of the amino acids we need, or have them in proportions that we can’t use perfectly efficiently, are “incomplete proteins.”

The PDCAAS reference basically asks: If you ate ONLY this food, would you actually be getting all the protein you need?