The Difference Between Complete and Incomplete Proteins

And how to know if you’re getting the right mix

Eating sufficient protein on a daily basis is important for keeping our bodies functioning efficiently. Without it, everything from our immune systems to our hair can take a hit. But when it comes down to it, the type of protein you eat matters, too.

Protein can be divided into two categories, complete and incomplete, based on its chemical structure. Knowing the difference between complete and incomplete proteins will help you figure out how to get the right mix of this essential macronutrient.

First, the basics: Protein is made up of amino acids, some of which the human body can make on its own, and others we need to get from food.

Amino acids are organic compounds that combine to form protein. They’re usually referred to as the “building blocks” of protein. “There are 20 different amino acids in the body—11 are nonessential, or those our body can make, and nine are essential, or those we cannot make and need to get from food,” , assistant professor of nutrition at the University of South Florida, tells SELF.

Just so you know, here’s that list of nine amino acids we can only get from the protein we eat: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Every amino acid plays an important role in building protein structures in the body. “Examples of protein structures in the body include: enzymes to help digest food, antibodies to keep the immune system strong, muscles and hair, and red blood cells,” Wright explains. “If we lack one or more essential amino acid, we are unable to build critical protein structures in the body.” Unlike fat and carbohydrates, our bodies can’t store amino acids for future use, so we pretty much have to get a little bit of each of them every single day.

Some of the protein sources we eat contain all nine essential amino acids; others are lacking.

“Complete proteins are those that have all nine essential amino acids that our bodies cannot naturally make, whereas incomplete protein sources may have a few of the nine, but not all of them,” Isabel Smith, M.S., R.D., C.D.N., founder of Isabel Smith Nutrition, tells SELF. Makes sense.

For the most part, animal protein is complete and plant protein is incomplete, though there are some exceptions. “The general rule is that animal foods—beef, chicken, fish, turkey, pork, and dairy—are complete, while plant foods—nuts, seeds, rice, beans, and grains—are incomplete,” says Wright. Bucking the trend are soy, quinoa, seitan, and buckwheat, which are all plant sources of complete protein.

If you eat a variety of healthy foods each day, chances are you’re getting all the right amino acids without trying—even if you’re vegan.

Meat, dairy, fish, and eggs are the most obvious sources of complete proteins. But even for those who don’t eat animal products, simply eating a combination of different proteins can give you all the essential amino acids—and that doesn’t mean just overloading on tofu and other soy products.

“In addition to soy and quinoa, vegans can expand their sources of complete proteins by complementing foods,” Wright says. “Complementing is when you take two incomplete plant proteins and put them together to receive all nine essential amino acids.” Some good examples she provides: rice and beans, hummus and pita bread, a peanut butter sandwich on whole grain, cereal with almond milk, and lentil soup with bread. To know exactly which amino acids you’re getting from different foods, you can use the USDA Food Composition Databases. But experts don’t think that’s necessary—simply mixing a variety of sources throughout the day (grains, legumes, nuts) should do the trick.

Experts used to think that you had to combine two complementary protein sources in one meal for this to work, but that’s been found to be untrue. “The new research says it doesn’t necessarily have to be all in the same meal, just over 24 hours, to combine to make a protein complete,” Smith says. You should be eating protein at every meal anyway, so as long as you’re getting a variety throughout the day and not just focusing on only one plant source, you should be fine. That would get boring real fast anyway.

For easy reference, here are some of the best sources of complete protein:

• Chicken
• Turkey
• Steak
• Pork
• Eggs
• Milk
• Cheese
• Yogurt
• Fish
• Tofu
• Quinoa
• Seitan
• Buckwheat
• Rice and beans
• Hummus and pita bread
• Peanut butter sandwich on whole grain bread
• Lentil soup with whole grain bread
• Stir-fry with peanut sauce
• Cereal with almond milk
• Trail mix (peanuts and sunflower or pumpkin seeds)

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“Instead, stick to regular, steady workouts a few times a week and maybe once on the weekends to properly build muscle, enhance your heart rate, and create actual strength, rather than tear down your body,” says Hall.