Jeremiah Farias

Sources of Protein: Are Some Better Than Others?

Written by Jeremiah Farias on March 7, 2020

Sources of Protein

We understand what protein is and the essential role is plays in our physiology and health, but where do we get protein? This may seem like a silly section to cover, but I am surprised on a daily basis when I ask clients where they or their children are getting protein and they will often list fruits and vegetables. While fruits, vegetables and some whole grains contain protein I would argue we should not rely on these as a primary protein source.

Why not? It has to do with protein quantity and quality.


When is comes to improving and/or preserving lean muscle mass, which I would argue is a key component to improve lifespan and healthspan, the quantity of protein in which one consumes at a meal and daily is important (due to Muscle Protein Synthesis, more on this later). Yes, one could get protein from broccoli, but is this ideal? People have even said 100 Calories of Broccoli has more protein than 100 Calories of Beef, but let’s see if this is actually true.

According to the Nutrition Coordinating Center Data Base (NCCDB) 105 kcal (this means Calories) of broccoli will give you 7.1 grams of protein. On the other hand, 101 kcal of 85% Ground Beef will provide you with 10.6 grams. So, I am not sure how the people making this claim are coming to this conclusion. Mind you, to get the 7.1 grams of protein from the broccoli, you would need to eat 300 grams (weight) of broccoli. One would need to only eat 42 grams of ground beef to receive the 10.6 grams of protein.

While broccoli and other vegetables may not be an appropriate comparison, how do foods deemed as plant proteins fare?

Let’s look at:

  • Soy Beans
  • Lentils
  • Peanut Butter

For simplicities sake, we will look at how 100 grams of the above mentioned plant proteins compare to 100 grams of 85% Ground Beef and Chicken Breast in terms of Protein Content and Calories per gram of Protein.

Grams of Protein that 100 grams of Chicken Breast, Beef, Soy Beans, Lentils, and Peanut Butter Provide

The bar graph above shows the number of grams of Protein in a 100 gram (weight) serving of each food. We can see chicken and beef are number one at ~31 g and ~26 g, peanut butter and soybeans are right behind, while lentils provide 1/2 the amount of protein that one would get from 100 g of soybeans.

While peanut butter looks pretty decent on this graph, it is helpful to look at how many Calories you would need to consume of peanut butter in order to reach 22 g of protein. Which we will do now.

Amount of Calories you receive per 1 g of Protein from Chicken Breast, Beef, Soy Beans, Lentils, and Peanut Butter

This bar graph illustrates the amount of Calories per each gram of protein. In order to reach 22 g of protein from peanut butter you would need to consume ~593 kcal (26.94 kcal x 22 g). If one is trying be mindful of caloric intake, for the sake of weight loss, peanut butter may not be the best choice. Beef, on the other hand, provides 9.27 kcal per gram, while chicken only provides 5.6 kcal along with each gram of protein. Soybeans can also be a good choice, as they provide a similar amount of Calories per gram of protein when compared to beef.

Overall, depending on the plant protein of your choosing, one may not have difficulty consuming adequate protein if they are vegan (I don’t mention vegetarian because they can consume eggs, which are a great protein source). While quantity does not seem to be a problem, according to the NCCDB, are their differences in quality between animal and plant sources of protein?


When looking at quality of protein, the following criteria need to be considered:


We will look at each point in the order they are listed, and again, to keep things as consistent as possible, we will use the five protein sources already mentioned and some new plant and animal sources given the data we have access to.

Amount of Profile of EAAs

Before, we looked at each protein source in 100 g portions because we were comparing protein quantity (grams of protein) and how many Calories each protein source provided per gram of protein (kcal/g of protein). Since we will be looking at quality, and specifically, how each protein source compares in their amount and profile of EAAs, we will look at each protein food source in a portion that provides 30 g of protein.

Chicken Breast - Source:
85% Ground Beef - Source:
Soy - Source:
Lentils - Source:
Peanut Butter - Source:

We see that a serving of Chicken Breast, providing 30 g of protein, meets the RDA (Recommended Dietary Allowances) for 8 of the 9 Essential Amino Acids (remember: tyrosine and cysteine or cystine are not considered essential), with the only exception being Leucine.

When compared to 85% Ground Beef, which hits 6 of the 9 EAAs, cooked soy beans do not look too bad. They meet the RDA for 4 of the 9 EAAs at a 30 g portion, while lentils and peanut butter meet the RDA for only 3 (though, 99% for histidine, in the case of lentils, is basically there).

*Note – In order to get 30 g of protein from peanut butter, one would need to consume a little over 800 kcal of peanut butter. This may not be the best source to depend on for meeting protein requirements.

So, when we compare the amount and profiles of EAAs in animal and plant sources of food, it is clear, in this instance, that animal sources have a better profile, with soy beans being the next best choice (plant source wise).

Next, let’s look at Bioavailability.


When looking at protein digestibility, many methods have been used, one being the Protein Digestibility Corrected Amino Acid Score (PDCAAS) (Gropper & Smith, 2013, pg. 239). The PDCAAS, though still referenced, utilized and valuable, is no longer preferred by the Food and Agriculture Organization of the United Nations (FAO). Instead, as of 2011, they utilize the Digestible Indispensable Amino Acids Score (DIAAS).

How does DIAAS determine bioavailability?

One consumes different foods, animal and plant foods, and the amount of amino acids remaining at the end of the ileum (the last section of the small intestine) is used to calculate a score. The closer the score is to 100%, the better bioavailability/digestibility. DIAAS can have values above or below 100%.

What foods end up scoring higher?

Data from FAO Food and Nutrition Paper & Nutrition Reviews. 2017 Aug; 75(8): 658-667

Animal Foods.

Unfortunately, I could not find data for the ground beef example we have been using, but this does illustrate the DIAAS when looking at plant vs. animal sources of protein.

It is clear, except in the case of Chickpeas, that animal sources of protein have better bioavailability/digestibility given their DIAAS, thus, can be considered as higher quality.

Lastly, in the case of protein quality, we will dive into MPS.

Stimulating Muscle Protein Synthesis (MPS)

First off, what is Muscle Protein Synthesis?

Muscle protein synthesis is the creation of muscle tissue, muscle hypertrophy. MPS can occur through exercise and through ingestion of protein rich foods. However, there is a caveat, just because a food has protein in it, does not mean it will stimulate MPS.

Secondly, before we discuss how to stimulate MPS via our nutrition, I believe it is also helpful to briefly explore why we would want to stimulate MPS in the first place.

Regardless of one’s age, muscle is important. However, muscle mass as one ages is especially important. Less muscle mass, which is usually accompanied by less strength, is associated with a higher risk of all-cause mortality (dying from anything). When you think about this, it makes sense. The less muscle and strength one has as they get older, the greater their fall risk. Unfortunately, along with low muscle mass and strength comes decreased bone density, which may result in the breaking of a bone along with the fall. Our muscles not only provide support and strength, but is a reservoir of amino acids in case our needs increase and are unable to obtain enough through our diet. In the case of an injury, like a broken bone, our need for protein (amino acids) increases. It is essential to the repair process and keeping our immune system functioning optimally, especially since most will find themselves in a hospital or rehabilitation facility at one point during that time, being exposed to many pathogens (remember, adequate amino acids are essential to our immune system).

What I mentioned may seem extreme, and more like a worse case scenario, but, it is actually very common. According to the CDC, falls are the leading cause of injury-related death among those 65 and older. It is best to start building muscle mass now, rather than later, and this is where nutrition and MPS become relevant.

In order for MPS to occur, the compound mTORC1 (mammalian/mechanistic target of rapamycin complex-1) is stimulated.

What causes mTORC1 to be stimulated via nutrition?

The amino acid leucine.

As you can recall, leucine can be found in both plant and animal foods. However, there is less leucine in plant foods, and, what matters is the amount of protein you actually digest and utilize. When we look at the DIAAS, not all of the amino acids are utilized when they are consumed due to fiber and anti-nutrients (more on these in another article).

In a controlled clinical trial conducted by Katsanos et al., they found that MPS was stimulated in the young group when they consumed a whey protein mixture containing 1.7 g of leucine, whereas the older group did not when given that dose of leucine. Instead, only when the older group consumed a dose of whey protein with added leucine providing a total 2.8 g, was MPS stimulated. The same was seen in a comparative study done by Paddon-Jones et al., where they found supplementing with EAA (essential amino acids) providing ~2.8 g of leucine stimulated MPS in the elderly where a 1.75 g dose did not. Lastly, research from Wilkinson et al., highlights that doses of leucine at 3 g have been shown to maximize MPS in young men and this is in the absence of other amino acids. So, if our goal is to maximize our ability to maintain and build muscle, aiming for around 3 g of leucine per meal may be beneficial. More on protein dosage per meal in Part 3.

It is difficult to specifically quantify how much of a given whole food, plant protein would need to be consumed in order to stimulate MPS to the same degree as a whole food, animal protein source. What is known, is a higher quantity is required when choosing plants.


That’s it for Animal vs. Plant Sources of Protein, and all that encompasses protein quantity and quality. Part 3, the last part, will discuss how much protein do we actually need, a practical way to measure protein, and a list of protein foods to refer to.

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Aragon, A. AARR. Nov. 2019.

Gropper, S.S. & Smith, J.K. (2013). Advanced Nutrition and Human Metabolism. Belmont, CA: Wadsworth.

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