Bioavailability

When we talk about protein, we often assume that 20 grams of protein is simply 20 grams of protein. But there is another consideration that is sometimes overlooked: bioavailability.

Bioavailability refers, among other things, to how much of the protein we eat is actually digested and absorbed by the body.

Protein from meat, fish, eggs, and dairy is generally highly digestible. Most of the protein is readily broken down during digestion and made available for absorption. Plant proteins, particularly those contained within intact foods such as beans, lentils, grains, nuts, and seeds, tend to be somewhat less digestible.

This doesn’t mean that plant protein is poorly absorbed. Far from it. Beans, lentils, soy, and other plant foods can make substantial contributions to our protein intake. But plant cell structures and naturally occurring compounds such as fiber and phytates can make some of their protein less accessible to digestive enzymes. Cooking and processing can substantially improve digestibility.

This raises an interesting practical question: If someone gets all of their protein from plant foods, should they simply assume that the number on the nutrition label represents the same amount of usable protein they would get from meat?

I don’t think that’s the best assumption.

A little animal protein can make things easier

For someone eating a predominantly plant-based diet, including a moderate amount of highly digestible animal protein can be a nutritional advantage.

For example, a diet might contain protein from beans, lentils, whole grains, nuts, and seeds, while also including some fish, eggs, poultry, or lean meat. The plant foods provide valuable fiber, vitamins, minerals, and other beneficial compounds, while the animal foods provide a concentrated source of highly digestible protein.

This can be particularly useful for older adults, who have a greater need to pay attention to maintaining muscle mass while often eating less food overall.

The point isn’t that plant protein is bad or that everyone needs to eat meat. A well-planned plant-based diet can provide adequate protein. Rather, there is little reason to make protein unnecessarily difficult to obtain by insisting that every gram come from plants.

Don’t overcorrect

At the same time, I wouldn’t recommend trying to calculate a precise “usable protein” number for every food.

Digestibility varies considerably among plant foods. Cooked beans aren’t the same as raw legumes. Tofu isn’t the same as a whole soybean. A plant-protein isolate isn’t the same as a grain. And a mixed diet makes the calculation even more complicated.

So I wouldn’t tell someone that they need to eat 25% more protein simply because their protein comes from plants.

A better approach is to eat sufficient total protein and obtain it from a variety of sources, including protein-rich plant foods and, if desired, moderate amounts of highly digestible animal protein.

The bottom line

Plant protein absolutely counts. But protein quantity isn’t the whole story.

The body has to digest and absorb the protein before it can use it, and animal proteins generally have an advantage in digestibility. For someone eating a primarily plant-based diet, including some highly digestible animal protein can therefore be a simple way to make meeting protein needs easier—particularly when maintaining muscle is a priority.

You don’t have to choose between plant foods and animal foods. A combination can give you the advantages of both.