Updated: Apr 29, 2020
In this article series I would like to summarize relevant protein-knowledge for gym-goers and athletes. Its not meant to be scientific, rather a simplified version of the available literature and consensus. Should you want to dig deeper therein, there exists more qualified people who can add to your education in that regard. Lassen uns beginnen.
What is protein?
It is one of the primary building blocks found in the human body. Its composed of smaller building blocks called amino acids (AA). There are about 21 different types of AA give or take, and they bind each other in various sequences to form different structural and functional molecules. We find these diverse proteins in our muscles, hair, nails, internal organs, skin, as signaling molecules, hormones, etc. This is important to know for a reasons explained later.
Protein is a macronutrient found mainly in meats, dairy and wheat products (although to a lesser degree), and is of extreme importance for building and retention of muscle and connective tissue; it can also be used as a form of energy, although the human body is not really efficient at it.
A gram of protein yields about 4 Kcals, although roughly speaking 20-30ish percent is lost in metabolic processing. Protein is, simply, everything good in life.
"Protein quality refers, in a general sense, to how well or poorly the body will use a given protein. More technically, protein quality refers to how well the essential amino acid (EAA) profile of a protein matches the requirements of the body; the digestibility of the protein and bioavailability of the amino acids (AAs) also play a role"
– The Protein Book, Lyle Mcdonald
This statement precisely explains what protein quality means. For most of us, this particular aspect of nutrition is irrelevant because at sufficient protein quantity and enough calories, quality ceases to be of importance in the big picture. To that end, everyone living in the modern World should not have problems in this regard.
This would be of more relevance of malnourished or hospitalized individuals; for example in clinical medicine we use various nutrient formulas for patients with different co-morbidities with the aim of optimizing their nutrient consumption, this is called parenteral feeding. Mind you these aren’t cookie cutter formulas; they’re often made from scratch for every patient which can be daunting. Thankfully its none of the physician’s business, at least not where I’m working right now.
Another factor that plays a role in the quality of proteins is micro-nutrient profiles; for example B12 and zinc in case of red meats, and calcium in dairy products. This is something to keep in mind when structuring a self-sufficient diet that covers all bases without need of supplementation.
Finally, protein digestibility is an often-overlooked component when structuring diets and when accounting for protein intake of different individuals.
Digestibility is how well your body breaks down a specific nutrient and how much of it is absorbed. Logically speaking, the more digestible a source, the more the body absorbs thereof, hence making better use of it.
When protein is ingested, its mechanically broken down in the mouth, then mechanically and chemically churned in the stomach, then further digested in the small intestines where most of the digestion takes place, after which it’s absorbed into the blood stream. The life cycle of solid protein is somewhere between 5-8 hours, possibly more depending on quantity and what it is mixed with (fibers, carbs, fat, etc).
Keeping everything in mind, below is the different digestibility scores of different but common foods based on the Protein Digestibility Corrected Amino Acid Score (PDCAAS):
This index evaluates quality of protein based on the amino acid profile and its digestibility by humans. Both the FDA and WHO use this index as a measure of protein quality. As you can see, you get more than 90% for all meats, and about 100% for dairy products and eggs. On the other hand, you get about 50% of the protein found in wheat products. This is crucial to grasp, because certain diets are reliant on these sources for their protein intake (vegan diets).
An example to illustrate the Written in the table: Suppose you have 100 grams of Beef, of which 20% is protein so that is 20 grams of protein. Digestibility is 90%, so out of those 20 grams that we ingest, 18 grams are absorbed by our bodies.
Lets look at a whole wheat as second example. 100 grams of whole wheat that has 20 grams of protein, digestibility is only 45% meaning our bodies only get 9 grams out of it.
That is literally half the protein absorbed from eating beef. Which means, double the amount of whole wheat is needed to get the same amount protein from Beef plus the extra calories and whatever else that will come with it.
Do you see now how important this is?
This concludes part 1 of the series, stay tuned for part 2 next week!