We tend to think of protein as a single nutrient — something you can find in a piece of grilled chicken or a couple hardboiled eggs. And while that’s all true, there are actually two kinds of protein: complete protein and incomplete protein. While it’s important to keep track of total protein to ensure you’re eating enough each day (this will help you build muscle mass and just generally keep your body running at peak condition), it also helps to know what kind of protein you’re eating. Here’s how to tell the difference between the two types, the importance of each, and ways to incorporate them into your diet.
What are complete proteins?
All proteins are composed of linked chains of molecules called amino acids. These amino acids perform a lot of important functions in the body, including building muscle, keeping your immune systems strong, regulating hormones, and making and repairing your cells.
There are 20 different amino acids, and they’re categorized into two categories: nonessential and essential. Eleven of the 20 are nonessential amino acids, which means the body is able to make them by itself. These include tyrosine, glutamine, and glutamic acid. The other nine amino acids are essential, meaning the body cannot make them and you need to get them from food. Essential amino acids include tryptophan, leucine, and lysine. To be considered a complete protein, the food needs to contain all nine essential amino acids that your body can’t make itself.
Complete protein examples
Most complete proteins are animal-based, like meat and dairy. In addition to providing all essential amino acids, these foods also offer other important nutrients, including vitamin B12, iron, and calcium. There are some plant-based complete proteins as well, though, including soy products — tofu, edamame, tempeh, soy milk — quinoa, hemp seeds, chia seeds, and pistachios. Here are some other examples of complete proteins:
Dairy
Milk, cheese, yogurt, and other dairy products are all complete proteins and can be good sources of protein in general. A cup of low-fat milk contains about 8 grams of protein while plain fat-free Greek yogurt has 23 grams of protein per 1 cup.
Eggs
One large egg contains 6 grams of protein, including all of the essential and many of the non-essential amino acids. Eggs are also good sources of vitamin B12, vitamin A, and choline, which helps with muscle and brain function.
Fish
Fish and seafood are good sources of complete protein. Many contain omega-3 fatty acids, which are anti-inflammatory and can protect against cardiovascular disease and cancer. Protein counts vary, but three ounces of cooked salmon provides 21 grams of protein, 3 ounces of cooked shrimp contains about 20 grams, and 3 ounces of cooked yellowfin tuna has 25 grams.
Meat
Beef, pork, and poultry are also complete proteins and, in the case of beef, can be a good source of iron. A 3-ounce piece of grilled boneless, skinless chicken breast and a 3-ounce cooked lean top sirloin steak both have 26 grams of protein while a broiled boneless pork chop contains 21 grams of protein per 3-ounce serving.
What are incomplete proteins?
Incomplete proteins lack one or more of the nine essential amino acids. Most plant sources of protein are incomplete proteins, including the majority of nuts and seeds, vegetables, beans and legumes, and whole grains.
Incomplete protein examples
Plant-based proteins are usually incomplete proteins, with some exceptions (as mentioned above, soy products, quinoa, pistachios, chia and hemp seeds are all complete plant proteins). Here are some examples of incomplete proteins:
Legumes
The term legumes is often used for both actual legumes (snap peas, snow peas, and peanuts) as well as pulses (the inner seeds of legumes, including shelled peas, beans, and lentils). Most legumes and pulses are incomplete proteins, with the exception being foods made from soybeans. Protein counts vary for different pulses and legumes, but one-half cup of peas has 4 grams of protein, one-half cup of cooked black beans has 8 grams, 1 tablespoon of peanut butter has 4 grams, and one-half cup of cooked lentils has 9 grams.
Nuts
Pistachios are complete proteins, but other nuts such as almonds, cashews, and walnuts are incomplete. Most seeds, like pumpkin and sunflower seeds, are also incomplete proteins (chia and hemp seeds are the two that are complete). In addition to protein, nuts and seeds contain fiber and healthy unsaturated fats, as well as magnesium, zinc, and other vitamins and minerals.
Whole grains
We don’t tend to think of grains as protein sources, but they are. Brown rice, oats, corn, and whole wheat offer some protein, along with fiber and other essential nutrients. Whole grains tend to be low in the amino acid lysine, which is what makes them an incomplete protein source.
Vegetables
Veggies don’t contain nearly as much protein as animal sources (and they are incomplete proteins), but some are pretty good sources, including spinach (5 grams of protein per 1 cup cooked), broccoli (4 grams per 1 cup cooked), mushrooms (2 grams of protein per ½ cup cooked), and Brussels sprouts ( 4 grams per 1 cup cooked).
Incomplete vs. complete proteins
Complete proteins contain all nine essential amino acids (the ones your body can’t make on its own) while incomplete proteins contain some but not all of those essential amino acids. You don’t need to eat complete proteins at every single meal, but you should try to have them as part of your daily diet.
“Each amino acid plays a different role in your body, so it’s important to get all of those amino acids at some point during your day,” says Kelli Richardson, Ph.D., RDN, a registered dietitian and a research consultant at WeightWatchers.
You may be tempted to focus solely on eating complete proteins, but incomplete proteins are great sources of other important nutrients that many animal products lack, including fiber and antioxidants. A balanced diet contains both types of proteins to ensure you’re getting adequate nutrition across the board.
Combining proteins
You can combine incomplete proteins to make what is essentially a complete protein, meaning the combo has all nine essential amino acids. This is particularly important if you’re following a vegan or vegetarian diet with zero or limited amounts of animal proteins.
Both Richardson and Alyssa Pacheco, RDN, a registered dietitian and owner of The PCOS Nutritionist, recommend these pairings of incomplete proteins to make a complete protein:
- Rice and beans
- Peanut butter and whole-grain toast
- Oatmeal topped with berries and nuts or seeds
- Hummus and pita
How much protein do you need?
The short answer is: It depends. “There are a few different ways you can determine how much protein you need,” says Richardson. “It could be based on body weight, age, activity level, if you’re on a GLP-1 medication, if you’re pregnant — there’s so many factors that can go into how much you actually need.”
For most people, Richardson recommends following the USDA Recommended Daily Allowance, which is a minimum of 0.8 grams of protein per kilogram of body weight per day. One kilogram equals about 2.2 pounds, so for a person who weighs 200 pounds, that would be a minimum of about 73 grams of protein per day.
But some people may need more, including anyone looking to lose weight or those taking a GLP-1 weight-loss medication. “People on GLP-1s need to get more protein because they are losing weight at such a fast rate and also losing some lean body mass,” Richardson says. The extra protein can help you hold on to as much muscle mass as possible. If that’s you, aim for a minimum of 1 gram of protein per kilogram of body weight.
You can go higher than those minimums as well. Pacheco, for example, recommends 1.2 grams of protein per kilogram of body weight. But again, this depends on the person. “For somebody who is strength training several times a week, their protein needs might look different from somebody who’s mainly walking and strength-training one time a week,” Pacheco says.
You can track your protein intake in the WeightWatchers app to see if you’re getting enough (just track all of your food and check My Day). And try not to stress too much about it. “If you’re following a relatively balanced diet, where you’re incorporating animal products, even if you’re not eating meat or seafood, you’re generally going to be OK in terms of getting enough complete protein sources and those essential amino acids,” Pacheco says.
The bottom line
Proteins can be separated into complete proteins and incomplete proteins. Complete proteins contain all of nine essential amino acids that your body cannot make by itself. Incomplete proteins are missing one or more of those essential amino acids. Most complete proteins are animal-based, like meat and dairy products, while incomplete proteins tend to be plant-based, like beans and whole grains. If you eat a varied, balanced diet, you will likely consume enough protein and get all of the essential amino acids each day.
FAQs
You could develop an amino acid deficiency, which could result in difficulty building and maintaining muscle mass and poor immune function, Pacheco says. But this is extremely rare. Most people have enough variety in their diets to get the essential amino acids, even if they’re only eating incomplete proteins.
Some animal-based proteins, such as beef and pork, contain high levels of saturated fat and cholesterol. Eating too much of these can increase your risk of cardiovascular disease. You also don’t want to ignore incomplete protein sources, since they tend to be plant-based and contain fiber and other essential nutrients.
Peanut butter is an incomplete protein, but you can pair it with whole-grain toast or swirl it into a bowl of oatmeal to create a complete protein.
This content is for informational purposes only and does not constitute medical advice, diagnosis or treatment. It should not be regarded as a substitute for guidance from your healthcare provider.