When you first hear the term “complete protein,” you may just think it’s one of those marketing buzzwords used to make products sound, well, healthier (see also: “all-natural”). But it’s actually a legit nutrition term—even if the meaning isn’t immediately clear.
Before we delve into what a complete protein actually is, let’s take a step back for a sec and talk about why all types of protein are important. One of the three macronutrients—along with carbs and fats—protein famously offers a post-workout boost, but that’s not all. “Protein’s important for more than just muscle building,” Desiree Nielsen, RD, a recipe developer with a focus on plant-based nutrition, tells SELF. Not only does it fill you up, she says, “it helps to keep blood sugar balanced, it’s important for bone health, and it’s important for immune function.” As for how much you need to reap these benefits? Sources differ, but Harvard Health reports that men and women should generally aim to consume about 46 and 56 grams per day, respectively (or, if you’re willing to do some math, about 0.36 grams per pound of body weight). If you exercise, though, that number climbs higher: The American College of Sports Medicine recommends active folks (like those who lift weights or are training for a running or cycling event) take in 0.5 to 0.8 grams per pound.
Okay, protein is super important, but how does a complete one fit into the picture? Read on to find out what a complete protein actually is, why they’re important, and the best way to fit them into your diet.
What is a complete protein, anyway?
To answer this question, let’s think back to high school bio class. You might dimly remember your teacher mentioning amino acids—molecules that combine to form proteins, otherwise known as the building blocks of life. There are a total of 20 amino acids, and they are divided into three main categories: essential, semi-essential (or conditionally essential), and non-essential.
“Non-essential means that our body can make them itself, so there’s no requirement to get them directly from food,” Nielsen says. Semi-essential amino acids are also synthesized by your body, but need to be supplemented during times of stress. Finally, “essential means the body cannot produce them at all, and it is imperative that we get them from food.”
Of the 20 amino acids, nine are considered essential: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Basically, complete proteins are foods that contain all nine in adequate amounts, and this includes most animal products, Janice Dada, MPH, RDN, a certified intuitive eating counselor based in California, tells SELF.
Both animal and plant proteins contain some combination of the 20 amino acids, but not necessarily all nine essential ones. In contrast to complete proteins, those that don’t contain all nine in adequate amounts are known as incomplete proteins.
Most plant products fall into this category, including beans, grains, nuts, peas, seeds, and vegetables. Usually, they’re considered incomplete proteins because they’re deficient in one or two of the essential amino acids—“what we call limiting amino acids,” Nielsen says.
