Do ‘Complete’ And ‘Incomplete’ Proteins Really Matter?

Whether you’re a resident of the weight room, a vegetarian, trying to lose weight, working to keep your blood sugar stable, or just want to be all-around healthy, a balanced, nutritious diet is key to reaching your goals. And a hugely important component of such a diet? Protein.

Not only does protein, which digests slowly and doesn’t spike your blood sugar, keep you satiated, but it’s also essential for just about every structure in your body, building muscles, hair, red blood cells, the immune antibodies that fight infections, and more,” says Brooke Alpert, C.D.N, R.N, M.S, founder of B-Nutritious.

When we think of protein, our minds often jump to animal products, like meat, milk, and eggs—but plenty of plant-based foods (like nuts, grains, and legumes) provide protein, too! That’s where one big question comes in: Are some proteins better than others? Glad you asked…

All proteins are made up of molecules called amino acids, which have various functions in the body—like breaking down food, supporting the body’s growth, and repairing tissues. There are 20 amino acids in total, nine of which are considered ‘essential’ because they can’t be produced by our body and must be obtained through our food. (The essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.) The other 11 amino acids are ‘nonessential’ because our body can make what it needs on its own. (These include alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.)

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You’ve probably heard animal proteins referred to as complete proteins, and that’s because they offer all nine of the essential amino acids. Plant proteins, meanwhile, are typically deficient in one or more of those essential aminos, and are thus incomplete proteins. (There are a few exceptions, however: Quinoa, hemp seeds, soy, and chia seeds are all complete proteins.)

Given that animal proteins are complete proteins, you’d think they’re the better protein source, right? Not necessarily.

By eating complementary proteins—two plant-based protein sources that fill in each other’s missing amino acids—you can even rack up all the aminos you need in one plant-based meal. For example, grains (like rice or whole-wheat bread) are low in the amino acid lysine but high in the amino acid methionine. Legumes (like beans or peanuts), meanwhile, are high in lysine and low in methionine. So, by eating the two foods together—think peanut butter toast or rice and beans—you’ve got yourself a complete protein! “There’s a reason why beans and rice have a staple in many cultures for years,” says Alpert. (Not to mention, it’s an affordable, non-perishable, and sustainable meal.)

Related: 7 Tips For Doing A Plant-Based Diet Right

That said, you don’t actually have to compensate for missing aminos every time you sit down to eat. “It is not necessary to combine incomplete proteins in every meal, or even every day,” says Sarah Skovran, R.D.N., L.D.  As long as you’re eating an adequate balance—and amount—of incomplete proteins on a regular basis, your body will be stocked with the amino acids it needs and can pull from its ‘amino acid pool’ as necessary, she says. In fact, research from the American Dietetic Association shows that eating an assortment of plant foods over the course of the day can provide ample amounts of all the essential amino acids and ensure adequate nitrogen retention (a marker of sufficient protein consumption) in healthy adults.

The bottom line: Most Americans consume more than enough protein—and don’t need to stress about whether they’re complete or incomplete—especially if animal products are a part of their diet in some capacity, says Alpert. Herbivores, however, should make sure to eat a variety of plant foods, including grains, beans, nuts, fruit, and plenty of vegetables. “If your plant-based diet contains only grains and no beans or nuts, you might be low in certain amino acids, like lysine,” says Skovran. “And if you eat beans and nuts, but no grains, then you could be low in others, like methionine.”

If you’re a vegetarian or vegan and don’t eat certain types of plant foods—or experience low energy or trouble building muscle—Skovran recommends seeing a registered dietitian who can make sure you’re getting all of the amino acids (and vitamins and minerals) you need.

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