Vegetarian protein is just as ‘complete’ as meat, despite what we’ve been taught

Huffington Post: “If you eat a dish with black beans, you’re not getting complete protein. You have to add another kind of bean to get the same kind of protein you’d get from meat.” 

This suggestion came from a generally well-informed acquaintance of mine while we were on a long car ride, making me wonder if the fumes had gone to her head.

Simmering with scepticism, I asked, “Adding any kind of beans will make it complete?”

“Yes, any kind of beans,” she replied with supreme confidence. “White beans, kidney beans, lima beans, lentils. When you combine any two beans, it’s just as good as eating animal-based protein.”

My instinct was to tell her she was wrong. But our drive through a countryside without cell towers or access to Google prevented me from doing so with absolute certainty. Now, however, I’m armed and ready to bust this myth.

It turns out my acquaintance was referring to a diet fad called “protein combining” that became popular in the 1970s. It was based on the premise that vegetarian and vegan diets provide insufficient content of essential amino acids, making it necessary to combine plant-based proteins to get the same “complete” protein you’d get from an animal. Protein combining has since been discredited by the medical community, but there are still people out there who adhere to this practice, and even more people who still believe plant-based protein is incomplete.

Concepts like “good fat vs. bad fat” and “good cholesterol vs. bad cholesterol” are somewhat well-known these days, but chatter about “incomplete protein vs. complete protein” hasn’t quite made it into the nutritional zeitgeist. You may have heard about complete protein if you’re vegan or vegetarian, but that doesn’t guarantee you fully understand what it is. Case in point: quinoa. Quinoa is often marketed as one of the only vegetarian sources of complete protein, but that’s a misleading claim because every plant-based protein is complete. There’s no information to support the idea that quinoa is a more complete source of vegetarian protein than other plant-based foods. Nor is meat, for that matter. Let’s get to the bottom of why.

Just to be clear, a “complete protein” is a protein that contains all nine of the essential amino acids our bodies need to function: tryptophan (the stuff in turkey that supposedly makes us sleepy), threonine, isoleucine, leucine, lysine, methionine+cystine, phenylalinine+tyrosine, valine and histidine. Those amino acids are “essential,” but our bodies can’t make them, so they must be derived from the foods we eat.

Though many vegans and vegetarians worry about getting enough protein, concern about “complete protein” intake has more to do with the quality of our protein than the quantity.

Dr. Michael Greger explains at his site NutritionFacts.org that all nutrients come from the sun or the soil. Cows, for example, get their nutrients from the sun and from plant-based foods like grass and hay. So if cows eat plants, and plants provide cows with all the nutrients they need, why would we assume steak is a more complete protein than the food that provides the steak with its nutrients? The answer: We shouldn’t.

While it’s true that some plant proteins are relatively low in certain essential amino acids, our bodies know how to make up for it. 

“It turns out our body is not stupid,” Greger explains. “It maintains pools of free amino acids that can be used to do all the complementing for us. Not to mention the massive protein recycling program our body has. Some 90 grams of protein is dumped into the digestive tract every day from our own body to get broken back down and reassembled, so our body can mix and match amino acids to whatever proportions we need, whatever we eat.”