Animal Proteins vs. Plant Proteins: How Do They Compare?

In recent times, we can hear the words “plant protein” much easier than we could in the past.

With the promotion of legumes such as lentils, beans, and the wide range of vegan “meat” products, there are many different plant proteins out there.

However, how do they compare with traditional animal proteins?

This article takes a balanced look at what the data shows about the respective protein quality of animal and plant foods.

What Is Animal Protein?

Animal protein refers to the dietary protein we can get from animal-based foods.

Some of the most popular sources of animal protein include;

• Dairy foods such as cheese, milk, yogurt, and whey
• Eggs
• Fish, shellfish, and other types of seafood
• Poultry from chicken, duck, and turkey
• Red meat such as beef, lamb, and pork

What Is Plant Protein?

Plant protein is simply a dietary protein from non-animal sources.

These plant proteins typically come from beans, legumes, nuts, and soy.

For instance, here are some of the most popular types of plant protein;

• Black beans
• Edamame
• Isolated proteins from wheat, pea, rice, etc
• Kidney beans
• Pea protein
• Soybeans
• Tempeh
• Tofu
• Various vegetarian/vegan burger products

How Can We Assess the Quality of Protein?

Firstly, the quality of protein can vary from food to food. In short, this means we can absorb and digest some proteins better than others.

For this reason, twenty grams of protein from some foods can be a better source than twenty grams of protein from another.

But how can we assess the quality?

There are two primary ways;

• The amino acid profile of the food
• Protein bioavailability ratings

Amino Acid Profiles of Animal and Plant Proteins

In this next section, we will analyze how much of each essential amino acid popular animal and plant proteins contain.

However, before we do this, let’s first look at the essential amino acid requirements.

According to the National Academies of Sciences, Engineering, and Medicine, we should strive to get the following daily amount of essential amino acids (1);

Amino Acid Profiles: Animal Proteins vs. Plant Proteins

In this next table, you can see the amino acid profile of four of the most popular animal proteins compared to popular plant proteins.

For this comparison, the animal foods are;

• Beef
• Chicken
• Eggs
• Salmon

You can see how these foods compare with four of the most popular plant-based proteins;

• Lentils
• Red kidney beans
• Tempeh
• Tofu

For each source, you can see the essential amino acids they contain based on a 100-gram (cooked) serving, as well as their overall protein content (2, 3, 4, 5, 6, 7, 8, 9);

As shown in the above table, meat and fish tends to provide the highest amounts of protein per gram.

Following meat, the soybean-based foods, tempeh and tofu, offer the next highest concentrations of protein.

After this, eggs are next, followed by kidney beans and lentils.

However, the total amount of protein and amino acids in food doesn’t tell the whole story.

As previously mentioned, the bioavailability of these amino acids is crucial, and the amount we can digest differs depending on the food.

Protein and Amino Acid Bioavailability From Animal and Plant Foods

It is important to be aware of how the protein bioavailability of foods may affect total protein intake.

For instance, choosing only low-quality protein sources could potentially result in a protein deficiency.

There have been many different systems that try to ascertain the quality of protein over the years.

Some of these have included the biological value (BV) and nitrogen balance.

However, the two protein quality scoring systems that hold the most value today are PDCAAS and DIAAS.

PDCAAS

Since 1993, the preferred way of determining protein quality has been the protein digestibility-corrected amino acid score (PDCAAS).

This system measures the quality of protein sources by looking at the amino acids they contain and how capable the human body is of digesting the total amount of protein (10).

DIAAS

In recent years, there have been proposals by the Food and Agriculture Organization (FAO) to replace the PDCAAS system with a new method of measuring protein quality.

The new proposed system is called the digestible indispensable amino acid score (DIAAS) (11).

One of the primary difference between PDCAAS and DIAAS systems is that the latter takes anti-nutrients into account. Anti-nutrients are compounds in plant foods that can limit the absorption of amino acids (and minerals such as zinc and iron) (12, 13).

Additionally, unlike PDCAAS, which assumes we digest all protein equally, the DIAAS score measures individual amino acid digestibility by analyzing fecal matter at the end of the small intestine (14).

PDCAAS Ratings For Protein Foods

First of all, we will look at the quality scores of animal and plant proteins based on the existing PDCAAS system.

These scores analyze the eight proteins we profiled earlier alongside some additional proteins (15, 16, 17).

(Note: the highest possible PDCAAS protein quality score is 1.0).

According to the PDCAAS ratings, which is the current standard for measuring protein quality, the most bioavailable proteins are;

• Dairy products like milk and whey
• Eggs
• Soy foods

Generally speaking, according to PDCAAS, all animal foods have a high protein quality rating.

For plant foods, there is a gap between soy-based products and the rest.

In particular, peanuts, red lentils, and kidney beans are quite a lot lower in protein quality.

DIAAS Ratings For Protein Foods

As discussed earlier, there is a new (and more accurate) proposed way of measuring protein quality known as DIAAS.

The DIAAS scoring system grades quality by the following classifications (18);

• DIAAS >100: high-quality protein
• DIAAS >75 and <100: good quality protein
• DIAAS <75: low-quality protein

Since DIAAS scores are relatively new, they can be difficult to find. However, the table below shows the available DIAAS protein quality scores for animal and plant proteins (19, 20, 21, 22).

Comparing animal and plant proteins via the DIAAS system shows a greater contrast than PDCAAS.

As shown, the amino acids in animal foods survive digestion better than those in plant foods, giving them a higher bioavailability.

According to DIAAS, all animal proteins are of high quality.

On the other hand, most plant proteins are low-medium quality.

However, it is worth noting that soy-based proteins are only slightly under the ‘high quality’ threshold.

For an in-depth guide to the highest-quality protein supplements, see here.

Animal Proteins vs. Plant Proteins: Which Are Better?

As shown in this article, if we look purely at the quality of protein, then animal proteins are the best choice;

• Animal proteins mostly have a higher total amount of protein and better amino acid profiles.

• The proteins in animal foods are more bioavailable than plant sources.

For these reasons, foods like dairy, eggs, fish, and meat are the most effective ways to get protein.

Considerations For Vegetarians/Vegans

For any vegetarian or vegans reading this, it is more challenging to get a sufficient amount of essential amino acids from a diet free of animal proteins.

However, that does not mean it isn’t possible.

By eating a higher amount of these plant foods, it is still possible to meet essential amino acid requirements.

As shown in the amino acid profiles and protein quality ratings, the best plant proteins tend to be soy-based.

Some different soy-based foods from around the world include;

• Cheonggukjang
• Edamame
• Miso
• Natto
• Tofu
• Tempeh

Final Thoughts

There are often many disagreements between animal and plant-protein proponents.

However, there doesn’t need to be; both sources of protein can provide our daily requirements for the nutrient.

That said, gram-for-gram, animal sources of protein tend to be the most effective way to meet these requirements.

For more on protein, see this guide to the macronutrient’s benefits.