Complete vs. Incomplete Proteins: What’s the Difference?

Written by: Angela Myers
Medically reviewed by: Ecler Ercole Jaqua, MD, MBA, DABOM

Protein is the “it” food group right now, and the hype is well deserved. However, there’s one important distinction that’s often overlooked: not all protein sources are created equal. Some are complete proteins while others are incomplete. Here’s everything you need to know about complete vs. incomplete proteins, and why you should add both to your diet.

The words “complete” and “incomplete” have very different connotations. The former sounds good or desirable, and the latter might conjure an image of something that isn’t whole. Yet when it comes to complete vs. incomplete proteins, these terms are a bit more neutral. Both types can support a healthy diet—and you don’t need every protein you eat to be ‘complete’ as long as you get a variety throughout the day.

Complete protein sources are those that contain all nine essential amino acids. The body can’t make these on their own, yet they’re crucial for building muscle, maintaining energy levels, and more. Incomplete protein sources are missing one or more of those essential amino acids. Incomplete proteins tend to come from plant-based products while complete proteins are typically found in animal products, though there are exceptions. 

“Neither is ‘bad,’,” says Allison Christel, MSN, FNP-C, a family nurse practitioner and founder of PlantRx, “It just requires a little more intention if you're building a plant-forward plate.”

Continue reading to get a  better understanding of these protein types, sources for both, and how to get enough protein, no matter if you’re a meat eater, a vegan, or a vegetarian like me.

Complete vs. incomplete proteins: the key difference 

Complete protein foods (and powders) contain all nine essential amino acids, while incomplete protein foods are missing one or more. Your body cannot make these essential amino acids, which is why you have to get them from your diet. 

For reference, the nine essential amino acids are:

1. Histidine: Has anti-inflammatory and antioxidant properties
2. Isoleucine: Plays a role in immune system function, wound healing, the secretion of multiple important hormones, and nitrogen balance, which supports metabolism and muscle growth
3. Leucine: Is involved in blood sugar regulation, muscle growth and repair, and wound healing
4. Lysine: Supports the immune system and helps promote tissue function, growth, and repair
5. Methionine: Essential for hair growth, tissue repair, and strong nails
6. Phenylalanine: Supports metabolic health and plays a part in mood regulation
7. Threonine: Plays a role in metabolism and supports the immune system
8. Tryptophan: Necessary for growth in young children and nitrogen balance in adults; plays a role in the production of serotonin, a neurotransmitter that regulates mood and behavior 
9. Valine: Helps promote muscle growth and repair

Generally speaking, animal-based proteins are more likely to be complete than plant-based ones (though there are exceptions, which we’ll get into below). Protein powders can be either complete or incomplete, depending on the specific product.

As a plant-based NP, Christel mentions that a big misconception is that complete equals better. Instead, she recommends combining many types of protein, aiming to get all nine essential amino acids from your weekly diet versus from one food. 

Do you need to combine proteins to make them “complete”?

You don’t need to carry around a checklist and make sure you get all nine amino acids from every protein source you eat. Instead, aim to get all nine throughout your day. The easiest way to do this is to eat a wide variety of whole foods. “ Your body pools amino acids throughout the day,” says Christel, “So variety over time is what matters.”

If you’re wondering what incomplete proteins work well together, here are some pairings that can help you get a higher proportion of amino acids:

• Rice and beans
• Peanut butter and bread (so long as it’s whole grain)
• Lentil soup with pumpkin seeds
• Whole wheat pasta and cheese
• Tofu and sesame sauce

What is a complete protein?

So, what is a complete protein, exactly? It’s a protein source that has all nine essential amino acids. Most are animal-based, meaning they come from animal products, such as meat, cheese, or eggs. 

But just because a protein is complete doesn’t mean it’s healthy. Some complete proteins, such as bacon or hot dogs, are ultra-processed and should only be enjoyed in moderation. That's part of the reason why the goal isn’t to eat any and all complete proteins. Instead, aim to get a variety of complete and incomplete proteins from whole foods and possibly a high-quality protein powder. 

Complete protein foods and complete protein sources

Popular animal-based complete protein sources include:

• Beef
• Pork
• Lamb
• Chicken
• Eggs
• Fish and shellfish
• Dairy milk
• Greek yogurt
• Cottage cheese
• All other dairy cheeses

Common plant-based complete protein sources include:

• Quinoa
• Soy foods (tofu, edamame, soy milk, etc.)
• Buckwheat
• Chia seeds
• Hemp seeds
  
  

What is an incomplete protein?

Incomplete proteins are missing one or more essential amino acids. But they still count toward your daily protein intake. Many incomplete proteins can be part of a healthy diet, and when you eat a variety of incomplete protein sources, it’s possible to get all nine amino acids throughout the day.

“Diversity is the real key,” says Christel, “Eat a wide variety of legumes, whole grains, nuts, seeds, and vegetables, and your amino acid bases are covered.” 

Incomplete protein foods

Legumes

• Lentils
• Beans
• Chickpeas
• Pinto beans

Whole grains

• Brown rice
• Oats
• Whole wheat pasta
• Whole wheat bread
• Barley
• Farro

Nuts and seeds

• Sunflower seeds
• Almonds
• Cashews
• Walnuts
• Hazelnuts
• Pumpkin seeds
• Pistachios

Vegetables 

• Broccoli 
• Brussel sprouts
• Asparagus 
• Mushrooms
• Spinach

However, whether or not a protein is complete or incomplete is only one part of the puzzle. You also want to pay attention to how much protein a food contains and how it fits into your overall protein intake. Cashews, for example, contain about 5 grams of protein per 1-oz. serving (about 18 nuts), while baby spinach has 2.85 grams of protein per 100-gram serving So while spinach and cashews are both “incomplete” proteins, one contains more protein than the other.

Whole protein foods vs. powders and blends

Whole protein foods are minimally processed foods that contain protein (either complete or incomplete). Christel says these should make up the foundation of your diet since they also contain fiber, vitamins, and phytonutrients which support overall health. 

However, protein powders still offer many benefits and can be a lifesaver on busy days (or every day if your life is hectic like mine). If opting for a protein powder, look for one that:

• Contains all nine amino acids: This may be easier to find in animal-based proteins, though there are plant-based protein supplements with all nine amino acids, such as Veracity’s Metabolic Power Protein powder.

• Lists all ingredients: Avoid products with "proprietary blends” that don’t spell out the exact ingredients included. Instead, look for a powder with a short list of natural, recognizable ingredients and the grams of protein per serving clearly marked. 

• Is certified by a credible third-party organization: Protein powders aren’t FDA-regulated, meaning the quality of the ingredients isn’t verified by the government. That’s why it’s important to look for a product that has been tested by a third party for contaminants. Those organizations also verify and label accuracy within the certification’s scope. Common third-party endorsements include USP verification or NSF certifications, such as NSF Certified for Sport.

• Produced in a FDA-reviewed facility: Purchase a powder made in a facility that follows the FDA Current Good Manufacturing Practices (CGMP). These manufacturers meet the minimum regulations for facilities that process food, drugs, or supplements.

• Tastes good: Protein powder quality matters, but so does taste. Pick one that you actually enjoy so you’ll use it more consistently. Flavors that taste good and work well in a variety of foods (smoothies, oatmeal, yogurt, etc.) include coffee, banana, cinnamon, vanilla, chocolate, and strawberry.

How much protein do you need?

There isn't a one-size-fits-all recommendation for protein intake. The ideal depends on your age, weight, gender, and lifestyle factors, including your physical activity level. To figure out your personal protein target, you’ll have to do a little math (but it’s easy, and I’m saying that as someone who hated every math class I ever took). The U.S. Department of Agriculture even has a calculator that can help.

Let’s start with the broad recommendation that applies to us all: 10% to 35% of your daily calorie intake should come from protein. The recommended daily calorie intake varies from person to person. If, for example, someone’s recommended calorie intake is 2,000, and somewhere between 10% to 35% should come from protein, that’s 200 to 700 calories per day.

If you prefer to count your protein in grams, divide the calories by four, since one gram of protein contains four calories:

200 calories divided by 4 = 50

That means the minimum amount to eat throughout the day is 50 grams of protein.

Why does protein matter for metabolism?

Metabolism refers to the processes within the human body that turn food into energy. Since these processes burn calories, we often associate metabolism with body weight, but it’s responsible for so much more. Metabolism helps us think clearly, breathe, regulate body temperature, digest food, and have the energy to do the things we want. 

Protein supports metabolism in a few key ways:

• Aids in muscle growth: Muscle burns slightly more calories than fat, promoting  long-term metabolic health. While eating protein doesn’t build muscle (that’s strength training’s job), it does provide the necessary amino acids to support muscle growth.

• Burns more calories: When you consume and digest protein, you actually burn more calories compared to carbs or fats—though a mix of all three helps you maintain overall health. 

• Catalyzes key enzymes: Many metabolic processes use protein as an enzyme catalyst. In other words, you can think of protein like an “on” button for some important bodily processes associated with metabolism. 

• Stabilizes blood sugar: One of the metabolic processes is breaking down food into blood sugar and helping that blood sugar get to cells that can use it as energy. Eating protein helps stabilize blood sugar levels and slows digestion, meaning you feel full for longer. Plus, your body’s cells receive energy more steadily throughout the day, rather than in spikes and crashes.

Together, these impacts mean protein plays a role in maintaining a healthy metabolism, which can have a tangible effect on everyday life. Christel regularly helps individuals get adequate protein in their diets, which she says helps them have sustained energy throughout the day.  

 

How to tell if you’re getting enough protein

As we’ve established, protein is important for muscle growth, hormonal health, enzymes, and more. “When you're not getting enough [protein], your body feels it across the board,” says Christel. She adds that signs you’re not getting enough protein can vary quite a bit. They include:

• Persistent fatigue, even if you’re sleeping enough
• Wounds heal slowly
• Loss of muscle mass or inability to grow muscle despite consistent strength training
• Sugar cravings strike often and are hard to ignore

When Christel works with someone on their diet, one of the first things she has them do is audit their typical protein intake. You can do this with a healthcare provider or on your own in a food journal—though it’s worth pointing out that people with metabolic conditions, kidney disease, or other chronic conditions may especially benefit from professional guidance.

5 easy ways to add more protein to your diet

If you find that you’re not getting enough protein, there are some simple ways to fix that.

1. Swap a carb-heavy snack for a handful of nuts or edamame 
2. Mix a serving of high-quality protein powder into your oats, yogurt, or smoothies
3. Try a protein ”habit stack”, e.g.making a smoothie with protein powder as soon as you get home from the gym
4. Sub white bread and pasta for whole grain options
5. Top salads or pasta with tinned fish, nuts, or both

There are also strategic ways to time your protein intake throughout the day. Frontloading the day with protein, for example, may help stabilize blood sugar and increase satiety. I’m a big fan of scrambled eggs or Greek yogurt for breakfast.

And eating protein after a strength-training workout can promote muscle adaptation, making it easier to build lean muscle.

Key takeaways

• Complete proteins contain all nine essential amino acids; incomplete proteins are missing one or more.

• While it’s important to eat all essential amino acids, you don’t have to get all of them from one food. Aim for a mix of incomplete and complete proteins, since variety is the spice of life (and good health).

• Protein should make up 10%-35% of your daily diet. For many people, a protein powder helps them reach that intake goal, allowing them to feel energized and strong throughout the day.

• If using a protein powder, opt for one that’s third-party tested and provides all nine amino acids, such as Veracity’s Metabolic Power Protein.
  
  

Frequently Asked Questions (FAQs)

Is Greek yogurt an incomplete protein?

Since Greek yogurt has all nine essential amino acids, it’s considered a complete protein, not an incomplete one. Greek yogurt is a nutrient-dense food that makes a great snack or protein-rich  addition to a meal. 

Is Veracity’s Metabolic Power Protein a complete protein source?

Yes. Veracity's Metabolic Power Protein is a plant-based blend of organic pea, organic pumpkin seed, and organic chia seed protein, and provides all nine essential amino acids, so your body gets everything it needs for muscle repair and recovery.

Are eggs incomplete proteins?

No—eggs are a complete protein. That means they contain all nine essential amino acids that the body requires to function normally.

What are 5 incomplete proteins?

Incomplete proteins lack at least one of the nine essential amino acids. Five foods that provide incomplete proteins include lentils, beans, oats, nuts, and seeds. 

What happens if you only eat incomplete proteins?

Complete proteins contain all nine essential amino acids that the body cannot produce on its own, whereas incomplete proteins are missing one or more. If your diet lacks all nine essential amino acids, you could have an increased risk of muscle loss and fatigue and compromised immunity. 

However, while there’s a risk of missing out on certain amino acids if you only eat incomplete proteins, it’s unlikely. Most people who eat a variety of proteins from different sources, even if they’re incomplete, will get all nine throughout the day. 

What is the unhealthiest protein?

Processed meats like hot dogs and bacon are usually considered  the unhealthiest protein sources.. Certain, but not all, protein powders and bars may be considered unhealthy as well, depending on their ingredients and how they’re processed. As with any supplement, choose one that’s been tested for contaminants and approved by a third-party organization, such as the United States Pharmacopeia (USP) or the National Sanitation Foundation (NSF).