Complete vs Incomplete Proteins: What’s The Difference?  

Even if you are following a plant-based diet, as long as you eat a wide array of legumes, vegetables, nuts, seeds, and whole grains and meet the recommendations for protein for adults, you should be getting an adequate amount of amino acids in your diet so that you are getting “complete proteins.“

But, what is a complete protein? What is an incomplete protein? What are some examples of complete proteins and examples of incomplete proteins?

In this complete vs incomplete proteins guide, we will cover the basics, what differentiates a complete vs incomplete protein, examples of each, and how to eat proteins in a way that provides your body with the nutrients of a complete protein.

We will look at: 

  • What Makes a Protein a Complete vs Incomplete Protein?
  • Complete vs Incomplete Proteins

Let’s get started!

The word protein written on a chalkboard surrounded by protein filled foods such as meats, cheese, legumes and nuts.

What Makes a Protein a Complete vs Incomplete Protein?

The Academy of Nutrition and Dietetics and the National Academy of Medicine recommend that for general health, the average adult should consume 0.8 grams of protein per kilogram of body weight.

In addition, the American College of Sports Medicine recommends that athletes consume at least 1.2–2.0 grams of protein per kilogram of body weight per day. 

Proteins are composed of building blocks known as amino acids. There are 20 amino acids, nine of which are considered “essential amino acids“ because your body cannot produce them naturally. Instead, you must consume them in your diet.

So, what is an incomplete protein, and what is a complete protein?

The difference between a complete vs incomplete proteins is that a complete protein contains at least some amount of all nine essential amino acids (and potentially some or all of the other 11 amino acids), while an incomplete protein is missing at least one of the nine essential amino acids that your body cannot produce endogenously.

Meat, eggs, fish and nuts.

Animal proteins, such as meat, poultry, fish, seafood, dairy, and eggs, are examples of complete proteins.

Many plant-based proteins, such as beans, vegetables, and rice, are examples of incomplete proteins.

It is possible to also pair complementary sources of incomplete proteins to provide your body with all of the essential amino acids in adequate amounts for optimal health.

In order to do so, it is helpful to understand which amino acids are considered essential amino acids, the functions of these amino acids, and most importantly, the recommended daily intake of the nine essential amino acids.

This will help you ensure that even if you are eating incomplete proteins from plant-based foods, you are meeting your essential amino acid needs.

The following provides a quick rundown of the nine essential amino acids—including some of the key functions (but not all) —along with the recommended daily intake of each amino acid, according to the Cleveland Clinic.

Meat, eggs, fish, legumes, cheese and nuts.

#1: Histidine

Essential Amino Acid Function:

Among the many functions of this essential amino acid, some of the notable are supporting the immune system, helping regulate sleep and sexual reproductive functions, and eating digestion.

This essential amino acid also helps form histamine, which is a nitrogenous compound involved in the immune response.

Recommended Daily Intake: 14 mg/kg of body weight

#2: Isoleucine

Essential Amino Acid Function:

Isoleucine is one of the three branched-chain amino acids (BCAAs).

These are essential amino acids with a particular molecular structure that are involved in energy production and repairing muscle tissue. Isoleucine also helps the body produce hemoglobin, which is the protein that helps carry oxygen in the blood.

Recommended Daily Intake: 19 mg/kg of body weight

Lentils, beans, tofu, bread and nuts.

#3: Leucine

Essential Amino Acid Function:

Leucine is a BCAA that plays a key role in muscle repair, wound healing, blood sugar regulation, and manufacturing of various proteins and growth hormone.

Recommended Daily Intake: 42 mg/kg of body weight

#4: Lysine

Essential Amino Acid Function:

This essential amino acid is involved in the immune system, and it also helps regulate calcium function and produce hormones and energy.

Recommended Daily Intake: 38 mg/kg of body weight

#5: Methionine

Essential Amino Acid Function:

Methionine is involved in energy metabolism, detoxification, and tissue growth and repair. It is also required for the absorption of certain essential minerals such as zinc and selenium.

Recommended Daily Intake: 19 mg/kg of body weight

Meat, fish, poultry, eggs and legumes.

#6: Phenylalanine

Essential Amino Acid Function:

Phenylalanine is a precursor for important neurotransmitters such as dopamine, epinephrine, and norepinephrine, as well as some of the other nonessential amino acids that the body can produce endogenously.

Recommended Daily Intake: 33 mg/kg of body weight

#7: Threonine

Essential Amino Acid Function:

Some of the functions of threonine include aiding the blood clotting process, metabolizing fat, and forming a component of collagen and elastin, which are structural proteins found in connective tissues and skin.

Recommended Daily Intake: 20 mg/kg of body weight

Hard boiled eggs.

#8: Tryptophan

Essential Amino Acid Function:

This essential amino acid is best known for its role in forming serotonin, a key neurotransmitter with numerous functions in the body, such as regulating mood, sleep, and digestion.

Additionally, tryptophan helps maintain the proper nitrogen balance in your body.

Recommended Daily Intake: 5 mg/kg of body weight

#9: Valine

Essential Amino Acid Function:

This BCAA supports muscle growth, tissue regeneration, and energy generation.

Recommended Daily Intake: 24 mg/kg of body weight

Although the main difference between complete vs incomplete proteins is whether or not the protein contains all of the 9 essential amino acids, both complete and incomplete proteins may also contain some or all of the other 11 amino acids.

Fish and meat.

These amino acids are generally considered to be “nonessential amino acids” because your body is able to produce them from other amino acids without needing to consume them directly in the foods you eat.

The nonessential amino acids include alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine. 

It’s important to note that some of the nonessential amino acids are classified as conditional amino acids.

This means that they become essential amino acids under certain circumstances, such as with chronic illnesses, pregnancy, or in times of high stress.

Although different sources cite slightly different conditional amino acid lists, arginine, cysteine, glutamine, tyrosine, glycine, proline, and serine are sometimes considered conditional amino acids.

Therefore, they should be taken into consideration when determining an incomplete vs complete protein if you fall under one of the high-needs or high-stress conditions.

Protein shake.

Complete vs Incomplete Proteins

Legumes such as beans, lentils, and chickpeas are examples of incomplete proteins that tend to be low in the essential amino acids methionine and cysteine.

Another example of an incomplete protein is vegetables such as spinach and broccoli.

While these vegetables do provide a good source of protein on a plant-based diet, like other plant-based foods, even “high-protein vegetables” (high protein here is a relative term compared to other vegetables that have a lot of proteins but have much less protein than lean proteins sources like fish, eggs, poultry, and soy) are still incomplete proteins.

Like legumes, most vegetables are also very low in the essential amino acids methionine and cysteine.

Therefore, pairing beans, lentils, hummus (which is made from chickpeas), or another legume with vegetables will still not provide a complete protein because both of these plant-based incomplete proteins are lacking the same essential amino acids.

Rather, to mitigate the downsides of incomplete vs complete proteins, you have to pair incomplete proteins that have complementary amino acid profiles.

This means that you have to choose examples of incomplete proteins that lack certain essential amino acids with other incomplete proteins foods that contain those essential particular amino acids but may lack other essential amino acids.

Whole grains.

For example, whole grains, seeds, and nuts are other plant-based foods that are incomplete proteins.

However, instead of lacking the essential amino acids methionine and cysteine, these example incomplete proteins tend to be low in lysine, a different essential amino acid that can be found in sufficient quantities in legumes and vegetables.

Basically, you are filling the gaps in the amino acid profile with your incomplete proteins foods by consuming various plant-based incomplete proteins from different food groups to cover your bases.

Here again, if you chose to eat oats, another example of an incomplete protein, with almonds, your meal or snack would still be very low in lysine because both of these incomplete protein foods lack sufficient amounts of lysine.

Instead, you’d want to pair whole grains with vegetables or legumes and nuts and seeds with legumes and vegetables.

However, the good news is that according to the National Institute of Health, you do not need to pair incomplete proteins in the same meal for your body to have all the amino acids it needs.

You can consume all of the essential amino acids with complementary incomplete proteins throughout the course of a day.

Also, there are a few plant-based foods that are considered complete vs incomplete proteins because they do, in fact, contain sufficient quantities of all nine essential amino acids.

Examples of plant-based complete proteins include soy, hemp seeds, chia seeds, nutritional yeast, quinoa, amaranth, buckwheat, and spirulina.

Alternatively, most plant-based protein powders are designed to be complete proteins, particularly if you choose hemp protein powder, soy protein powder, or a plant-based protein powder blend that combines different incomplete proteins.

To learn more about meeting your protein needs, check out our guide that discusses how much protein you should eat in a day here.

A person drinking a protein shake.
Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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