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 the main points of interest that I feel are important to the general public.
The protein comprises building blocks called amino acids for brief background information. It is generally accepted that the body utilises ~20 Amino Acids. Nine amino acids are essential; 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 0 – 100% scale. This is just one of the 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 detail the 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 is ~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, other factors must be taken into consideration, being that people are not usually eating beef protein alone. The amount of fat 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. Regarding bioavailability, it is ~80%, with digestibility of ~98%. While 98% may be digested, only 80% is incorporated into body tissues.
With less fat in the meat, chicken can be seen as a faster-digesting protein source than 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 controversial topic within the last year, with concerns about phytoestrogen content, especially in women. This post will concentrate strictly on soy protein and its BV. According to a study review in 2004, soy protein bioavailability is ~74%, with a digestibility of 96%. Although not horrible, it may not be as bioavailable as other proteins.
With so many types of protein out there, I cannot possibly cover them all, but I 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 regarding BV and digestibility, they should not be 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. On the other hand, beans can provide the amino acid lysine but lack 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 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, you must have adequate amounts in your diet.
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