Complete and Incomplete Proteins: Differences and Sources - Step To Health

Complete and Incomplete Proteins: Differences and Sources

In the following article, we'll talk about complete and incomplete proteins. What are their differences and the most prominent sources? Find out here!
Complete and Incomplete Proteins: Differences and Sources

Last update: 21 December, 2021

Talking about complete and incomplete proteins is a recurring debate in the world of nutrition, as is the right amount of these nutrients to eat daily. However, there can sometimes be some confusion about these terms.

Protein is a component of food that plays an important role in the body. It’s involved in building bones, muscles, tissue repair, and hormone synthesis. It even plays a role in the feeling of satiety and the maintenance of muscle mass after physical exercise.

Fortunately, it’s present in a wide variety of healthy foods, such as eggs, fish, lean meat, legumes, soy, and all its derivatives. Which ones are complete and which ones are incomplete?

Here, we’ll tell you the answer.

Proteins: A basic nutrient for the daily functioning of the body

Proteins are essential substances for life, as they’re necessary for the structure, function, and regulation of different tissues and organs. The functions they perform are very specific and can be detailed as follows.

Repair and maintenance

Protein molecules are the building blocks of the body. Organs and many tissues are made up of them. For example, the hair, nails, skin, tendons, and muscles all are made up of protein. Because of this, they’re very important in times of growth, development, and repair (after surgery or in some diseases).


Enzymes are protein molecules necessary to carry out all chemical reactions in the body. They’re the most numerous and specific type of protein in the body.

Immune system support

Antibodies are also made up of amino acids manufactured by the immune system to prevent infections, diseases, and illnesses.

Transport and storage

Proteins are also involved in the transport or storage of certain molecules. This is the case of hemoglobin, through which oxygen and ferritin is transported (the latter is a protein that allows iron to be conserved in the liver).


Also, proteins are involved in the synthesis of certain hormones. These, in turn, are involved in many bodily functions. Some of the best known are insulin, growth hormone, secretin, or prolactin.

Energetic needs

This macronutrient is also a source of energy for daily functions. If we consume more than the necessary amount, the body uses the surplus for this purpose.

Proteína animal y proteína vegetal: ¿cuáles son sus diferencias?
Protein sources can be complete or incomplete according to their amino acid profile.

The composition of proteins is key to distinguishing between complete and incomplete proteins

On a structural level, proteins are chains of amino acids joined together through peptide bonds. That said, knowing some details about amino acids is key to distinguishing between complete and incomplete proteins.

When consumed, protein foods are digested, and free amino acids are absorbed. The cells then use these to create proteins, either in muscle building, hormone synthesis, tissue repair, etc.

Hundreds of amino acids are found in nature, but it’s estimated that only about 20 are needed by the body to perform all its functions. Moreover, of these, nine are considered essential. They’re the following:

  • Phenylalanine
  • Histidine
  • Isoleucine
  • Leucine
  • Lysine
  • Methionine
  • Threonine
  • Tryptophan
  • Valine

They’re known as essential because the body can’t synthesize them by itself. This means that they must be ingested with food. Otherwise, they would not be able to complete all their functions. Plus, they’re differentiated between complete and incomplete according to the quantity and type that each protein chain contains.

The differences between complete and incomplete proteins

We’re talking about complete proteins when we’re referring to the nine essential amino acids in quantities similar to those the body needs to develop its functions. On the contrary, those sources in which some essential amino acid is not found in sufficient amounts are known as incomplete.

In general, all foods of animal origin are considered a source of complete proteins. On the other hand, most plant proteins are usually incomplete, although there are some exceptions.

Complete protein sources

  • Fish and seafood
  • Eggs
  • Poultry meat (chicken, turkey, and duck).
  • Red meat (beef, pork, or lamb).
  • Dairy products (milk, yogurt, cheese, etc.)

Incomplete protein sources

  • Legumes (chickpeas, lentils, beans)
  • Whole grains (rice, wheat, rye, millet, etc.)
  • Nuts (almonds, peanuts, cashews, walnuts, among others)
  • Seeds (pumpkin, hemp, or sunflower)

Among the latter, it should be noted that they’re called “incomplete,” but it’s not due to the total lack of any of the amino acids. As you can read in the Medical Journal of Australia (MJA), only a few are not at the levels that would be considered necessary.

For many years, there has been talk of combining plant foods to obtain a protein as good as that of animal origin. Thus, rice dishes with lentils, pasta salad with nuts, or wholemeal bread with hummus are common options.

However, at the end of the day, your amino acid profile can be complete with only plant sources (incomplete). It’s enough to ensure that energy intake is sufficient and, of course, you eat a variety of foods throughout the day.

So, there’s no need to be afraid of a protein deficit if you want to follow a vegan diet or reduce the presence of meat in your diet. Moreover, in recent years, scientific evidence links the intake of vegetable protein sources with greater longevity and better health.

Diferencias entre proteínas completas e incompletas
Most plant-based foods have incomplete proteins. However, the combination of several such foods can help meet daily requirements.

Final things to keep in mind about complete and incomplete proteins

Proteins are a basic nutritional component that must be provided every day with food. They’re made up of amino acids and, depending on their structure, can be classified into complete and incomplete proteins.

Incomplete proteins may imply that they are inferior or not optimal for the body. However, in reality, this is not the case, since combining different incomplete sources throughout the day makes it possible to obtain all the essential amino acids for the body to function properly.

Whatever the source, it’s necessary to emphasize the quality of the food. Choosing legumes, whole grains, lean meats, eggs, oily fish, dairy products without added sugar or nuts is a good way to provide the necessary protein every day.

In addition, it’s important to keep in mind that, apart from the amino acids present in a food, other parameters condition the use of protein by the body. These include the digestibility of the food, your age, and the physiological state of each person.

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