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| Last update November 11, 2021, article reviewed & updated multiple times since July 14, 2001. |
What You Need to Know
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Today we are starting our discussion of protein. In this series, we will be looking at such subjects as what protein is, why protein is necessary, what the functions of protein in our bodies are, where we get protein, what happens if we don’t have enough or the right kinds of protein, and how and where in the system is protein digested. There will be a few surprises down the line.
What Does ‘Metabolism’ Really Mean?
Let’s talk for a minute about the word ‘metabolism.’ We all use it a lot, but are you actually clear on just what it means? Metabolism means the sum of all the physical and chemical processes whereby protoplasm (that is, all living tissue) is produced and maintained. Metabolism does not mean whether or not you put on or take off weight easily or with difficulty.
Metabolism is divided into two kinds of actions, the building-up processes, and the tearing-down processes. The building-up of substances into more complex structures is called anabolism (a-NAB-o-lism). The breaking down of complex structures to their component parts so they can be rebuilt into something else, or excreted as waste products, is called catabolism (ca-TAB-o-lism). Anabolism and catabolism are important concepts in understanding proteins.
What Is Protein?
The word protein comes from a Greek word meaning “most important.” Proteins are the basis of all protoplasm, of all living tissue. Proteins are composed of nitrogen in combination with carbon, hydrogen, and oxygen. Some also contain sulfur, phosphorus, or other basic elements. The amount of protein in any food is determined by analyzing that food for the amount of nitrogen present because it is the nitrogen part of protein that is crucial.
But proteins are compounds of biological origin. They cannot be synthesized (that is, built-up by anabolism processes) by people from the nitrogen in the air or from nitrogen in some other inorganic form. We must eat protein, which means that humans must eat other organisms that were previously alive. There is no getting away from this. We cannot eat stones, even if a variety of stones could be assembled that were made palatable, and that contained all the basic and required elements of life.
Some Of The Functions Of Proteins
Proteins perform many functions in the body. Here is a partial list to give you an idea of their importance. Proteins are required for: the growth of children, healing in both children and adults, the maintenance of all body flesh, bone, and hair, normal blood coagulation, the formation of immune compounds for disease prevention, the regulation of the amounts of fluids in the tissues, the water balance of the blood, the transport of oxygen in the blood, the formation of all enzymes, the maintenance of the sense of sight, the maintenance of fertility, the formation of hormones, and the production of substances necessary for the digestion of fats. The list could go on for weeks! Furthermore, every protein molecule in the body is continually changing and renewing its structure.
Protein structures are composed of varying numbers of various kinds of building blocks called amino acids. Proteins differ from one another in the total number of amino acids in them, in the number of each kind of amino acids in them, and in the arrangement of the amino acids relative to each other.
There is virtually an endless number of possible protein combinations. Consider a hypothetical protein structure containing only four of the 22 or so generally known amino acids. If each of the four was used only once, they could be arranged in 24 different combinations. A protein made up of only one each of the 22 has so many possible combinations it would require at least 27 numerals to write it, and the number would fill most of this entire line of print. The number of all possible protein arrangements is a figure too large to contemplate, let alone write. This explains why there can be such a tremendous diversity of tissues, functions, and enzymes in the millions of different plants and animals in the world.
As with complex carbohydrates, complex food proteins are utterly unfit for consumption by the cells. Since food proteins are the only supply of necessary nitrogen required for living things, the proteins must be broken down by digestion to the amino acid stage for absorption into the cells, where they recombine to make the various protein structures of life. Each tissue selects what it needs from the “buffet” of amino acids that circulate in the blood, based on what that particular tissue needs for formation, growth, repair, or renewal. Amino acids constitute the form in which protein is presented to the tissues, just as glucose constitutes the form in which carbohydrate is presented.
Essential Amino Acids
At the building-block level, the human body requires some 22 different amino acids, but not all of them need to be present all the time because the body is able to use some amino acids to make others. It does this in the cells by reforming the amino acids and recombining them into the ones that are missing, as necessary. This is called synthesis.
But there are about eight amino acids that the body cannot manufacture. These are referred to as essential amino acids. However, this is an unfortunate phrase because it tends to give the impression that some of the amino acids are “nonessential.” This is not the case; they are all essential for life. It is just that the body can make some of them from others. More precise terms would be synthesizable amino acids and non-synthesizable amino acids.
We now come to one of the ‘tricky’ aspects of protein metabolism. Amino acids are not stored for any appreciable time in the body. The essential amino acids must be eaten pretty much at the same time as the others. The synthesizable ones are not stored, waiting around for one of the missing “essentials” to show up later. Food proteins lacking one or more of the essential amino acids cannot sustain life. These foods are known as incomplete proteins or inadequate proteins. Some examples of food containing incomplete proteins are gelatin, corn, and most flour.
Diets that are deficient in the non-synthesizable amino acids lead to the breakdown of protein structures in the body, such as muscle. Since skeletal muscles contain the necessary proteins, the body will break down those proteins and take them in order to provide what is necessary for other protein functions. If it continues, eventually this will lead to a serious loss of muscle, grave malnutrition symptoms such as those seen in the Third World, and even death.
Those of us living a low carbohydrate lifestyle have no worries in this regard. The good news is that a diet of mixed animal protein ensures the ingestion of an adequate mixture of the essential amino acids. Unfortunately, a diet that is exclusively vegetable usually does not. Any person who decides that living on vegetables only is a good idea had better learn, and soon, exactly how to get all the essential amino acids by the precise mixing of appropriate vegetables, such as eating corn with certain kinds of beans.
Stay Tuned In!
Next time we’ll consider the digestion of protein and the waste products produced by the breakdown of protein. Please join me.
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The Science of Low-Carb & Keto Diets
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Article History
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| About Dr. Beth Gruber Dr. Gruber is a graduate of the Southern California University of Health Sciences and has been in private chiropractic practice in Long Beach, California since 1964. She also received both a Bachelor’s Degree and a Master’s Degree from California State University at Long Beach. She has written on health-related subjects for over 30 years, for several different publications. She lives in Southern California with her husband of 33 years. Both she and her husband follow and live the low-carb lifestyle full time. |
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