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.
| DIAASa | PDCAASb | |
|---|---|---|
| Animal-derived foods | ||
| Whey protein isolatee | 1.00 | 0.99 |
| Whey protein concentratee | 1.07 | 1.00 (1.07) |
| Milk protein concentratee | 1.20 | 1.00 (1.21) |
| Skimmed milk proteine | 1.05 | 1.00 (1.12) |
| Whole milk powdere | 1.16 | 1.00 (1.16) |
| Caseine, f | 1.09 | 1.00 (1.20) |
| Cow milke | 1.16 | |
| Sheep milke | 1.09 | |
| Goat milke | 1.24 | |
| Whole egg, boilede | 1.13 | 1.00 (1.05) |
| Beefe | 1.12 | 1.00 (1.14) |
| Porke | 1.14 | 1.00 |
| Chicken breaste | 1.08 | 1.00 (1.01) |
| Tilapia (fish)d | 1.00 | |
| Non-animal-derived foods | ||
| Soya protein isolatee | 0.84 | 0.93 |
| Soya floure | 0.89 | 0.98 |
| Wheate | 0.45 | 0.50 |
| Pea protein concentratee | 0.62 | 0.75 |
| Cooked peasf | 0.58 | 0.60 |
| Oat protein concentratee | 0.67 | 0.69 |
| Cooked rolled oatsf | 0.54 | 0.67 |
| Rice protein concentratef | 0.37 | 0.42 |
| Cooked ricef | 0.60 | 0.62 |
| Ryee | 0.48 | 0.59 |
| Barleye | 0.47 | 0.59 |
| Pease | 0.65 | 0.79 |
| Sorghume,f | 0.29 | 0.29 |
| Cooked kidney beansf | 0.59 | 0.65 |
| Roasted peanutsf | 0.43 | 0.51 |
| Corn based breakfast cerealf | 0.01 | 0.08 |
- Only values that used the scoring patterns for children older than 3 years, adolescents, and adults were selected
- aValues for DIAAS were calculated from the ileal digestibility of amino acids
- bValues for PDCAAS were calculated from the total tract digestibility of crude protein
- cAll values for DIAAS and PDCAAS were selected in humans, if available, growing pigs, or in growing rats in that order
- dMeasured in humans
- eMeasured in pigs
- 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 Acid | 1 oz Broiled Sirloin Strip Steak | 1 oz Broccoli | Ratio |
|---|---|---|---|
| Tryptophan (mg) (% RDI) | 55 (20%) | 9 (3%) | 6.7x |
| Threonine (mg) (% RDI) | 332 (32%) | 25 (2%) | 16x |
| Isoleucine (mg) (% RDI) | 378 (27%) | 22 (2%) | 13.5x |
| Leucine (mg) (% RDI) | 661 (24%) | 37 (1%) | 24x |
| Lysine (mg) (% RDI) | 703 (33%) | 38 (2%) | 16.5x |
| Methionine (mg) (% RDI) | 217 (30%) | 11 (1%) | 30x |
| Phenylalanine (mg) (% RDI) | 329 (38%) | 33 (4%) | 9.5x |
| Valine (mg) (% RDI) | 412 (23%) | 35 (2%) | 11.5x |
| Histidine (mg) (%RDI) | 265 (38%) | 17 (2%) | 19x |
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.
Conclusion
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.