Protein, one of the three big macronutrients, is widely considered to be essential for muscle growth, but it is used in so much more. It’s vital in maintaining a strong immune system, bones, teeth, and tendons, and also links to weight loss.

That being said, there is a major misconception that all proteins are equal which unfortunately isn’t true. Quality protein is essential but sometimes is hard to know what counts as “high-quality” protein. You might think it would be hard to see which protein sources are “high-quality” but it is easier than you think.


What are the high-quality protein sources?

The full list of high-quality protein sources is the following…

  • Dairy products; milk, whey powders, cheese, and cottage cheese, yogurt
  • Eggs
  • Seafood and fish
  • Beef
  • Chicken
  • Bison
  • Pork
  • Pea Protein
  • Soybeans
  • Blended meals (beans and rice)
  • Vegan protein powders with multiple protein sources

Many of the high-quality sources of protein are animal-based and while plant-based proteins aren’t as good a source of protein as their animal counterparts, consuming plant-based proteins will add a good boost to your protein consumption.


What makes a protein “high quality”?

A high-quality protein really is a function of three things which are digestibility, amino acid content, and the resulting amino acid availability.

The process of digesting any food begins in your mouth when you chew. But protein is unique among the three major macronutrients in that your body’s digestion of it truly begins in the stomach and continues into the small intestine.

Within those organs, acidic digestive juices, powerful enzymes, and other components fully break down intact proteins into smaller chains of amino acids, the building blocks of protein. It is only when these amino acids are available that the body can then use them for growth and repair.

Digestion also means that the conversion of protein to amino acids isn’t 100% so quality counts. The higher quality of the protein, the higher the number of amino acids and the greater the percentage that is absorbed into the bloodstream.

Scientists can now measure a protein’s digestibility in the lab by monitoring nitrogen absorption and excretion. (Protein is the only macronutrient that contains nitrogen, which is why this works.)  The outcome of this test typically produces a digestibility score.

Proteins that are highly digestible receive scores close to 100% (digestible). Lower scores are less digestible. If you were to consume a protein with a digestibility score of 90%, then for every 10g you consumed, you would absorb 9g and excrete 1g.

In general, animal proteins — such as dairy, eggs, and meat — score highly. Vegetarian proteins typically score lower.


What are amino acids?

Every protein is made up of amino acids, and the constitution of those amino acids determines the quality of the protein.

Your body can produce many amino acids on its own. But there are some it can’t make. They are:

  • histidine
  • isoleucine
  • leucine
  • lysine
  • methionine
  • phenylalanine
  • threonine
  • tryptophan
  • valine

These are the “essential amino acids,” and you must get them through your diet.

Any food that contains all nine essential amino acids is known as a “complete protein.”

Animal protein sources mimic the protein composition of human tissue. This is why meat naturally offers a highly usable blend of amino acids—including all nine essential amino acids (with some exceptions, which we’ll get to in a second).

As a result, we humans can use protein from an animal source in a very efficient manner. This includes dairy, which supplies a wealth of amino acids, including a high amount of leucine. So perhaps it’s not surprising that studies involving chronic exercisers have found that consuming milk-based protein after resistance exercise promotes muscle protein synthesis, more muscle, and less flab.


What About High-Quality Plant Protein?

Most plant sources (but not all) have an amino acid profile that differs drastically from that of humans.

Many (but not all) plant proteins are low in various essential amino acids, especially leucine. This is important to note because leucine plays a critical role in turning on muscle protein synthesis (MPS), which is key for building and repairing muscle tissue.

The big exceptions are soy and select sources of pea protein (like pea protein isolate). These vegetarian sources contain all, or nearly all, of the essential amino acids you require.

Outside of those sources, most plant-based proteins are not complete. All this means is that consuming one lone source of plant protein cannot support body growth and maintenance.

But there’s a simple fix. If you combine different plant protein sources, then you can receive adequate amounts of all nine essential amino acids.


So really, your main takeaways here are:

The exact amount of protein you need will depend on the quality of the protein you eat.

If you consume a lot of plant-based protein or are exclusively plant-based, you may need to increase your total daily protein intake, even more, to compensate for the lower protein quality.

If you are vegetarian or vegan, eat a diverse mix of foods, and you may want to research the amino acid profiles of the foods you eat.