Among the dietary challenges of vegetarians and vegans, perhaps none receives more attention than the eternal search for sufficient protein. For those on a plant-based diet, it can be hard enough to compete with the sheer density of protein provided by meat and dairy products, but throw in the need to combine complementary proteins and it can seem nearly impossible.

If you’re new to the concept of incomplete proteins, read on. Below we’ll discuss what they are, how they vary, and which to combine in order to make them complete.

What Are Complementary Proteins?

Protein pairing is the practice of combining plant-based foods that are missing or are low in one or more specific amino acids — which are the building blocks of protein — in order to round out your overall protein intake. There are 20 different amino acids, but only nine are deemed essential. That means your body can’t produce them, so they must be derived from food.

Foods with all nine essential amino acids (EAAs) score high in biological value and are deemed “complete proteins.” While all animal proteins are complete proteins, few plant foods meet that criterion. But you can still get all your EAAs from plant-based foods by combining them. That’s complementation… complementarity… complementiasis — whatever you call it!

You can think of amino acids like beads on a protein necklace: By stringing different numbers and types of beads, your body can create infinite possibilities of tissues, hormones, etc. It’s to your benefit to have as many beads lying around just in case you need them.

Complete vs. Incomplete Plant Proteins

You can count the number of complete plant proteins on one finger: At present, soy is the only confirmed plant-based protein that’s complete, despite common wisdom to the contrary. That makes it an ideal protein source for vegans and explains its ubiquity as a meat substitute.

But you can get all of your EAAs from plant sources — it simply requires some dietary balance. Beans (except soy), grains, nuts, seeds, and vegetables are incomplete protein sources since they’re missing or don’t contain enough of one or more EAA. But together they can form complete protein profiles.

The handy chart below explains which amino acids are missing from which plant food and what to pair it with to get all nine EAAs. Rice and beans, for instance, is a classic example of protein complementation.

Should You Eat Complementary Proteins at the Same Time?

Simultaneous protein complementation was advocated in the past, but it’s now generally believed that you can get away with consuming them within the same day or so. “Vegetarians and vegans don’t need to worry about complementing foods at every meal. Just shoot for a well-balanced diet,” Maguire advises.

How to Combine Complementary Proteins

Even after reading this, the bean counters (see what we did there?) among us may still want to pair complementary proteins anyway. If it makes your protein accounting efforts any simpler, complementary protein pairings appear naturally in many traditional cuisines:

• Beans and rice
• Peanut butter and wheat bread
• Hummus and pita
• Tortilla chips and bean dip
• Oatmeal and almonds
• Barley with lentil soup

Clearly, there are lots of delicious complementary protein pairings. Here are three rules of thumb for those who are considering protein complementation:

1. Choose high-protein foods

If you’re following a calorie-restricted diet, it’s a good idea to choose more protein-dense plant-based foods — nuts, seeds, beans, tofu, etc. — to ensure you meet your daily needs without blowing your calorie budget. (You should still eat avocado, mushrooms, oatmeal, spinach, broccoli, and kale; they all contain protein, just not a lot.)

You’re also getting fiber without loading up on calories. Win-win.

2. Eat a variety of plant-based proteins

The more varied your diet, the less important protein complementation becomes. With a tight budget, variety can be a struggle. In that case, pair a few high-protein foods whose amino acid profiles complement each other (see chart above).

3. Load up on complete proteins

Eggs, Greek yogurt, cottage cheese, and low-fat milk can boost protein intake for some vegetarians. Clearly they won’t work for vegans, who can instead take advantage of organic soy-based foods like tempeh, tofu, and edamame.

Why It’s Harder for Vegetarians and Vegans to Get Enough Protein

A high-protein diet is prized among highly active people because protein enhances recovery and promotes performance. Consuming protein after exercise also helps stimulate muscle growth and build strength. And if you cut calories for weight loss, a high-protein snack can help stave off hunger and preserve muscle mass even as you shed pounds.

Unsurprisingly, vegetarians and vegans eat less protein than omnivores. And as a group, athletic individuals need more protein than the population at large. “It’s common to recommend that vegan and vegetarian athletes eat 10 percent more protein than non-vegetarian athletes,” says Krista Maguire, RD, senior nutrition manager at BODi.

That’s because plant proteins generally score lower in digestibility than their animal counterparts. Therefore, vegetarians and vegans must make smart protein choices to get enough nutrients to reach their dietary and fitness goals.