Animal vs Plant Protein

Amino Acids

Proteins consist of units called amino acids. There are 20 amino acids. The body synthesizes some of them from components within the body, but it cannot synthesize 9 of the amino acids—called essential amino acids. They must be consumed in the diet. The amount and type of each amino acid vary based on the protein source.

Animal proteins such as eggs, milk and steak are complete because they contain all of the essential amino acids that your body needs to function effectively.

Plant proteins, such as beans, lentils and nuts are considered to be incomplete, as they lack one or more of the essential amino acids that your body needs.

Protein Quality Score

Due to the important role proteins play in our nutrition, it’s vital that we have a standard measure to determine protein quality.

PDCAAS (Protein Digestibility-Corrected Amino Acid Score)

In 1993, the Food and Agricultural Organization (FAO) and the US FDA made PDCAAS the official standard for comparing protein quality.

DIAAS (Digestible Indispensable Amino Acid Score)

In 2013, FAO proposed using a new evaluation method resulting in different scores called DIAAS. According to DIAAS, protein quality can be categorized as follows:

  • No protein quality claim – Score of <75%
  • Good protein quality – Score ranging from 75% to 99%
  • Excellent or High protein quality – Score of 100% or more

As you can see in the table below, all animal-based proteins are of high quality whereas plant-based proteins are either just good or poor in quality.

Animal-derived foods
 Whey protein isolatee1.000.99
 Whey protein concentratee1.071.00 (1.07)
 Milk protein concentratee1.201.00 (1.21)
 Skimmed milk proteine1.051.00 (1.12)
 Whole milk powdere1.161.00 (1.16)
 Caseine, f1.091.00 (1.20)
 Cow milke1.16 
 Sheep milke1.09 
 Goat milke1.24 
 Whole egg, boilede1.131.00 (1.05)
 Beefe1.121.00 (1.14)
 Chicken breaste1.081.00 (1.01)
 Tilapia (fish)d1.00 
Non-animal-derived foods
 Soya protein isolatee0.840.93
 Soya floure0.890.98
 Pea protein concentratee0.620.75
 Cooked peasf0.580.60
 Oat protein concentratee0.670.69
 Cooked rolled oatsf0.540.67
 Rice protein concentratef0.370.42
 Cooked ricef0.600.62
 Cooked kidney beansf0.590.65
 Roasted peanutsf0.430.51
 Corn based breakfast cerealf0.010.08
  1. Only values that used the scoring patterns for children older than 3 years, adolescents, and adults were selected
  2. aValues for DIAAS were calculated from the ileal digestibility of amino acids
  3. bValues for PDCAAS were calculated from the total tract digestibility of crude protein
  4. cAll values for DIAAS and PDCAAS were selected in humans, if available, growing pigs, or in growing rats in that order
  5. dMeasured in humans
  6. eMeasured in pigs
  7. fMeasured in rats

Essential Amino Acid Comparison Between Steak and Broccoli

Since essential amino acids are essential, it’s important and interesting to compare how much of them you get when you compare the same amount of an animal protein to a plant protein. The following table compares 1 oz of steak to 1 oz of broccoli.

%RDI = % Recommended Daily Intake

Essential Amino Acid1 oz Broiled Sirloin
Strip Steak
1 oz BroccoliRatio
Tryptophan (mg)
(% RDI)
Threonine (mg)
(% RDI)
Isoleucine (mg)
(% RDI)
Leucine (mg)
(% RDI)
Lysine (mg)
(% RDI)
Methionine (mg)
(% RDI)
Phenylalanine (mg)
(% RDI)
Valine (mg)
(% RDI)
Histidine (mg)

As you can see, you get WAY more essential amino acids from 1 oz of steak than you do from 1 oz of broccoli. However, from a calorie point of view,

  • 1 oz of Broiled Sirloin Strip Steak has 60 calories
  • 1 oz of Broccoli has 10 calories

1 oz of steak has 6 times as many calories as 1 oz of broccoli.

So, what if you just ate more broccoli to consume the same amount of amino acids as steak. The highest number in the ratio column is 30x. So, you’d need to eat 30 oz of broccoli to get at least the same amount of amino acids as steak. But then your calorie intake would be 10 calories x 30 = 300 calories, which is way more than 60 calories for the 1 oz of steak.


Don’t be a vegetarian. Include animal-based proteins such as eggs, meat and milk in your diet. If you don’t like them, then at least drink a smoothie made with whey protein powder. Here are some nutrients you can’t get from a vegetarian or vegan diet.