Is Animal-based and Plant-based Protein Equivalent?

is animal protein and plant protein equivalent and what is the Digestible Indispensable Amino Acid Score [DIAAS]Some people are considering going “plant-based” for perceived health reasons, or for ethical considerations and while these are important, evaluating plant protein quality is a necessary consideration. Evaluating protein quality using the Digestible Indispensable Amino Acid Score [DIAAS] can help.

A recent study found that essential amino acids from animal protein are more bioavailable than from plant protein [1], and these findings are especially important for older adults who need to preserve muscle mass, and for active adults wanting to build muscle. 

Amino Acids and Bioavailability

Amino acids are the building blocks of protein, including muscle. There are twenty amino acids categorized into two groups: essential amino acids (EAA) and non-essential amino acids.

Bioavailability means the degree to which the essential amino acids in a food can be used by the body to make its own proteins [2] such as muscle.

Essential amino acids, including leucine, which is required for muscle growth and repair, must be eating in protein foods in the diet. This is why they are called “essential” amino acids. The leucine content of a protein is vital because leucine is what triggers mTOR signaling in muscle, which stimulates muscle growth[3]. Dietary Recommendations for older adults emphasize obtaining 2.3 g leucine at each of 3 meals to ensure the building of new muscle protein [4], and 3g leucine per meals [5] to rebuild muscle. Protein recommendations for older adults range from between 20g per meal [3] to 25-30g protein per meal [5] for those recovering muscle mass. For physically active adults, the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine recommend a protein intake of 1.2—2.0 g protein / kg per day to optimize recovery from training, and to promote the growth and maintenance of lean body mass [6].

Plant Protein vs Animal Protein for Building Muscle 

chickpeas and hummus as example of plant protein - low Digestible Indispensable Amino Acid Score [DIAAS]Plant protein generally contains lower levels of the essential amino acid leucine than animal proteins[7] but those seeking to eat a more plant-based diet often turn to legumes (“beans”) for protein. Most legumes are incomplete proteins – meaning they are missing essential amino acids. For example, lentils have only 0.7g of leucine per half cup and chickpeas contain only 0.42g of leucine per half cup.  This means that so for an older adult to get the minimum amount of leucine at a meal (2.3 g leucine) they would have to eat more than 3 cups of lentils, or 5 ½ cups of chickpeas at a meal.

But what about the protein content of foods? Are plant-based proteins equivalent to animal-based proteins?

Is Plant Protein Equivalent to Animal Protein?

A newly randomized, investigator-blinded, crossover study was first performed with a group of young adults, and then in a group of older adults [1]. Researchers compared ounce-equivalents (oz-eq) of animal-based protein (lean pork or whole eggs) with plant-based protein (black beans or sliced almonds) in a mixed whole foods meal. The goal was to see how well the body can use essential amino acids from each type of protein to make body protein. To determine essential amino acid bioavailability, as well as blood sugar and insulin levels, blood samples were taken before they ate the meal, and at 30, 60, 120, 180, 240, and 300 minutes after eating.

Researchers chose the measure of ounce-equivalent (oz-eq) because the Dietary Guidelines for Americans (DGA) uses ounce-equivalent to “identify the amount of (protein group) foods with similar nutritional content” [1, 8]. For example, the DGA indicates that one ounce-equivalent equals one ounce of meat, or one whole egg, or 0.25 cups of beans, or 0.5 ounces of nuts but the authors of the study note that the ‘basis for stating these protein foods are “equivalent” and have “similar nutritional content” is unclear’ [1].

plant protein equal to animal protein ? What about the Digestible Indispensable Amino Acid Score [DIAAS]
“ounce-equivalent” from [8] U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020–2025, 9th ed


As pointed out by the authors, protein foods differ in energy content and macronutrient contents, including both protein quantity, and protein quality. With regards to protein quantity, one ounce-equivalent of pork loin contains ~7 g of total protein, and one ounce-equivalent of almonds contains only ~3 g of total protein [1]. 

With regards to protein quality, the authors define this ‘as the ability of a dietary protein source to provide adequate amounts and proportions of essential amino acids (EAA) that are digestible and as a result are bioavailable for use in the body for stimulating protein synthesis, and maintaining or growing body tissues’. 

The Bioavailability of Plant Protein – Digestible Indispensable Amino Acid Score

The bioavailability of amino acids in different types of proteins have been determined and is available in the The Digestible Indispensable Amino Acid Score [DIAAS]. In 2013, the DIAAS was recommended by the Food and Drug Administration to replace their previous method called the Protein Digestibility Corrected Amino Acid Score (PDCAAS) [9]. In the DIAAS system, each essential amino acid is recognized as an individual nutrient, rather than lumping all amino acids together and this is very important because the bioavailability of a protein source must to be taken into account when determining if a diet is adequate in protein, and in specific essential amino acids such as leucine.

High quality proteins are those with a DIAAS score ≥100, and are considered excellent quality proteins. DIAAS scores of 75–99 are considered high-quality proteins, and those with scores of <75 are considered to be able to make no quality protein claim [8]. Based on this recent research, plant protein from most grains and legumes (“beans”) are <75 on the DIAAS score, with pea and soy falling between 75 and 100.  Animal protein such as pork consistently score over 100 on the DIAAS [10].

If regulatory guidelines such as the Dietary Guidelines for Americans and Canada’s Food Guide for Health Eating used the protein values generated by the Digestible Indispensable Amino Acid Score, rather than the PDCAAS, consumers would easily be able to see that a 4oz plant-based patty is not equivalent in protein quantity of quality as a 4oz beef patty, and 20g of vegan protein powder is not equivalent to 20g of whey protein powder. Use of the DIAAS in both countries would more accurately reflect protein quality [11] and enable consumers to make better choices.  

Plant Protein versus Animal Proteins – conclusions of the study

plant protein vs animal protein for building muscle - steak as example of animal proteinThe study found that consuming meals with equivalent amounts of animal-based proteins versus plant-based proteins resulted in more essential amino acids in the blood compared with meals containing animal-based proteins in both young and older adults, separately and combined.

Also found was that there was greater essential amino acid bioavailability in lean pork, than in eggs in both young adults and older adults, separately or combined, and there as no difference in essential amino acid bioavailability between black beans and almonds.

The researchers concluded that it is inappropriate to say that different protein sources on an ounce-equivalent basis are “equivalent” .

Final Thoughts…

If you are an active adult seeking to build and repair muscle, then knowing which is better (plant protein vs animal protein for building muscle) is important. If you are an older adult wanting to retain muscle mass, eating high quality protein that contains all the essential amino acids including leucine is essential. While the US Dietary Guidelines states that one ounce of meat or one whole egg or 0.25 cups of beans or 0.5 ounce of nuts are equivalent, this recent study finds that the protein in beans and nuts is not equivalent to that in meat and eggs. 

If you are toying with the idea of becoming more plant-based, be sure that you understand the science of protein bioavailability so you can make a sound decision. 

For those who already eat a vegetarian diet for religious or ethical reasons, ensuring that your meals contain the most bioavailable plant-based proteins at each meal requires knowledge and effort.

More Info

If you would like support ensuring that you or someone you love eats sufficient high-quality protein at each meal needed to trigger muscle synthesis, please reach out to me through the Contact Me form, above.

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