With protein being the macronutrient of interest in the media recently, I thought I would provide some additional information on the various types of protein and their utilization when ingested. Although this post is not all-inclusive, I will touch on main points of interest that I feel are important to the general public.
To give some brief background information, protein is made up of building blocks called amino acids. It is generally accepted that there are ~20 Amino Acids utilized by the body. Nine of these amino acids are essential, meaning without them the body cannot synthesize the necessary proteins to maintain homeostasis.
After a protein-containing food is ingested, it is broken down into individual amino acids in the stomach and small intestine. These amino acids are subsequently reassembled into proteins used by our body through protein synthesis. This is a gross simplification, but gives enough context for those who do not have a scientific background.
It is a common misconception that all proteins are created equal. Depending on the type of protein ingested, Protein bioavailability, that is, how well your body can utilize a specific type of protein, can change drastically. (1) Protein bioavailability is measured as a biological value on a scale of 0 - 100%. This is just one of numerous metrics used to measure protein quality.
Another metric commonly used to measure protein quality is the PDCAAS (protein digestibility-corrected amino acid score). PDCAAS is measured on a point scale of 0 - 1.00. This compares the digestibility of all other protein containing foods to the protein availability of an egg, which is said to be the most bioavailable source of protein. (2) Although whey is now seen as the new gold standard. Below I will go into detail on bioavailability and digestibility of various protein sources.
Whey is one type of milk protein, the other major one being casein. Whey is commonly used surrounding workouts for its fast digestibility and bioavailability. The bioavailability of whey protein is said to be ~100% and the digestibility ~99%. (3) Therefore whey is a highly bioavailable source of protein, but not all people choose to consume it for ethical or health reasons.
When it comes to beef protein there are other factors that must be taken into consideration being that people are not usually eating beef protein alone. The amount of fat that the meat contains can change the speed of digestion. This is one of the reasons why beef is known as more of a slow digesting protein. In regards to bioavailability it is ~80%, with a digestibility of ~98%. This means that while 98% may be digested, only 80% in incorporated into body tissues.
With less fat contained in the meat itself, chicken can be seen as a faster digesting protein source when compared to beef. While the rate of digestion will vary depending on which cut of chicken you are eating. (breast, thigh, wing, etc.) Chicken has a bioavailability of 79% and a digestibility of 91%
Soy has been a rather controversial topic within the last year with concerns about phytoestrogen content, especially in women. For this post I will concentrate strictly on soy protein and its BV. According to a study review in 2004, soy proteins bioavailability is ~74% with a digestibility of 96%. Although not horrible, it may not be as bioavailable as some other proteins.
With so many types of protein out there I cannot possibly cover them all but just wanted to list a few other notable protein sources and their BV. Pea protein has a fairly poor BV at 60% with a digestibility of 73%. Oat protein is also not great at 55% and 57% respectively. Peanuts have a decent BV of 83% but their digestibility is lacking at 52%. Lastly rice protein has a BV of 64% and a digestibility score of 47%. Although these proteins may not be of top quality in term of BV and digestibility, this just means that they should not serve as a primary protein source.
Although not all proteins are complete , when multiple incomplete protein sources are combined, they can create a complete protein. This is called the complementary effect of proteins. The classic example is rice and beans. While rice provides numerous proteins, it is lacking in lysine. Beans on the other hand can provide the amino acid lysine but are lacking in methionine. When rice and beans are combined they can provide a complete protein. Some other complementary protein examples are dairy and nuts or tofu and rice. The complementary effect is what allows vegans and vegetarians to meet their nutritional needs while avoiding many animal products.
As you may now realize, not all proteins are created equal. Next time you see a food product on the shelf boasting about its protein content, think twice about the source of the protein. While it is not necessary to always eat complete proteins, it is important that you have adequate amounts in your diet.
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1. Millward, Joe, Donald Layman, Daniel Tome, and Gertjan Schaafsma. "Protein Quality Assessment: Impact of Expanding Understanding of Protein and Amino Acid Needs for Optimal Health." American Society for Clinical Nutrition 87.5 (2004):Web.
2. Schaafsma, Gertjan. "Advantages and Limitations of the Protein Digestibility-corrected Amino Acid Score (PDCAAS) as a Method for Evaluating Protein Quality in Human Diets." British Journal of Nutrition Br J Nutr108.S2 (2012): n. pag. Web.
3. Hoffman, Jay, and Michael Falvo. "Protein: Which Is Best?" Journal of Sports Science and Medicine 3 (2004): 118-30. Web.