Some protein sources are better than others, according to science. Here’s how to tell whether a protein is—or isn’t—high quality.

You’ve probably heard that you need more protein in your diet — and for good reason.

You might think of protein as the main building block for muscle, but it’s so much more.

Protein is also essential for maintaining a strong immune system, bones, tendons, and is responsible for many metabolic reactions. There is also clear relationship between protein and weight loss.

Here’s the thing:


Quality counts. But what’s the difference between protein and “high-quality protein?”

It can be a confusing distinction and one that doesn’t receive enough attention.

The good news: Distinguishing high-quality protein from lesser-quality protein is easier than you might think.

Your high-quality protein sources

If you just want a list of high-quality protein sources, we have you covered. The top sources are:

  • 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

If you want to better understand why all proteins are not created equal, then keep reading.

You might notice that the majority of the high-quality options are from animal sources. That’s simple because, by and large, animal proteins are of higher quality than their veggie-sourced counterparts. You’ll soon learn why.

But never fear, plant-based friends: you can still fill your diet with the protein you need even if you never want to put any animals in your mouth. We’ll show you how later in this post.

What makes a protein “high quality”?

A high-quality protein really is a function of three things:

  • protein digestibility (i.e. “Can your body break it down?”)  
  • amino acid content (i.e. “What’s really inside the protein?”)
  • the resulting amino acid availability to support metabolic function (i.e. “Will your body be able to use those amino acids the way you want it to?”) .  

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.

Before a chain can be absorbed into the bloodstream, it must be shortened into individual amino acids. Only then, when these amino acids hit the bloodstream, can they be transported to working tissues, reassembled into larger proteins that the body needs.

They may also be held for a short time with other amino acids in what’s referred to as an amino acid pool. The body can turn to this pool and take the exact amino acids it needs to create a larger protein molecule required for one function or another, and leave behind what it doesn’t require at the moment.

While the process might appear cut-and-dry, it’s not that simple. And like many processes within the body, it isn’t 100 percent perfect.  In other words, less than 100 percent of the protein you consume will be digested, absorbed, and put to use.

Scientists can measure a protein’s digestibility in the lab is 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.

But there’s another wrinkle in the process. Your body’s ability to absorb nutrients compared to its actual requirements don’t always line up.

Amino Acids: What’s Inside Your Protein?

Every source of protein has a different amino acid profile. These amino acids — or the component parts that a protein will become when you digest it — are a big determinant of whether or not a protein is high quality.    

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.”

Why Animal-Based Protein is the “Easy Button”

Animal protein sources mimic the protein composition of human tissue. Which 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.

Animal proteins range from the obvious—beef, pork, chicken, eggs, and fish—to fluid sources such as milk. All of these are high-quality protein sources that are highly bioavailable (your body can put them to use easily).


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.

While collagen and bone broths are popular for their potential to support joint health and other tissue function within the body, collagen protein is high in only 3 amino acids (glycine, proline, and hydroxyproline) while being fairly devoid of the other essential amino acids.

Bone broths may deliver health benefits, but they alone won’t help with muscle building or fat loss (or satisfy your body’s amino acid requirements, unless you add chicken or beef to the broth, in which case, you’re all set.)

What About High-Quality Plant Protein?

Conversely, 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.

Examples of complementary proteins include combining legumes and grains, such as red beans and rice, or vegetables and legumes, like you’d find in a 9-bean vegetable soup.


You don’t have to do this at the same meal. Your body will store the amino acids as they come in, and then resynthesize proteins as it needs by pulling from body cells and blood supplies later. So even if you had rice at breakfast and beans at dinner, you’re covered.

Often you need to eat more plant-based protein to get the equivalent amount of amino acids that you would from a smaller amount of animal protein.

So really, your main takeaways here are:

  1. The exact amount of protein you need will depend on the quality of the protein you eat.
  2. 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.
  3. 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.