Perhaps more than any other macronutrient, protein is the most consistently mentioned. In fact, it means literally “of first importance/quality.” When we think of protein, we think mostly of what we are eating, and while that will be mostly the focus of this article, proteins extend far beyond what’s on the end of your fork. Proteins are building blocks of all living organisms, creating the structures that support their cells, functioning as hormones to organize our life processes, creating antibodies to safe-guard our being, acting as catalysts in the form of enzymes, as well as having thousands of other functions. Protein is the most abundant molecule in the human body, with the exception of water. Because of proteins’ vast array of functions, it is the nutrient primarily used to build and rebuild tissues within our body, such as your muscles.
Protein as a macronutrient differs from the others in that it is a large molecule composed of amino acids linked together by peptide bonds. The are 22 amino acids important to our health, as they serve important functions in our body, and are divided into three categories: essential amino acids, non-essential amino acids, and conditionally essential amino acids. Essential amino acids cannot be produced by our body, and as such must be acquired from the foods that we eat. Non-essential amino acids on the other hand can be created by the human body through the breakdown of proteins during digestion, provided enough protein is ingested. Conditionally essential amino acids are usually non-essential, except in times of stress, such as illness.
There are nine essential amino acids including leucine, isoleucine, valine, lysine, threonine, methionine, phenylalinine, tryptophan, and histidine. Non-essential amino acids include alinine, asparagine, aspartic acid, and glutamic acid. Conditionally essential amino acids include arginine, cysteine, glutamine, glycine, proline, serine, and tyrosine.
All food contains some protein, as it must in order for whatever organism it came from to survive – the only exception is if a food is processed from its natural form. Primarily we think of protein deriving from animal sources, such as beef, chicken, fish, milk products, and eggs. It can also be found in plant sources, such as legumes, grains, roots and tubers, seeds, nuts, vegetables, and fruit. Foods are classified into two groups when it comes to proteins: sources of complete protein and sources of incomplete proteins.
Sources of complete protein are foods that contain the full array of amino acids as required by the human body. Most frequently this includes sources of animal protein, but can also include exceptional plant foods such as quinoa and chia seeds. Sources of incomplete protein are foods that do not contain all amino acids in significant amounts as required by the human body, which primarily includes plant based foods.
There are some important caveats to this that will be touched on in future articles, but especially includes the source from which meat derives. For example, a cow fed a diet that is unnatural or atypical from what it would normally eat (ie. consisting primarily of corn and other grains), may lack specific amino acids required by its own body, as well as the human body, as opposed to a cow fed its natural diet of only grass.
The human body is a magnificent engine, and as such, it is not necessary to eat food containing only complete proteins. So long as our food is not derived from a single source of calories, our bodies are able to break down proteins from a vast array of foods and obtain whatever it may require to function. While it is important to eat a wide variety of foods to obtain the nutrients (not only protein) your body requires, it is even more important to eat a wide variety of foods if your diet does not contain sources of complete proteins. A way of thinking about this is to imagine a ‘pool.’ When your body breaks down proteins, it takes amino acids and adds them to the pool. As you continue to ingest and break down more proteins, it takes the amino acids and again adds them to the pool. When your body requires specific amino acids, it is able to gather what it requires from the pool, and assimilate them into the specific proteins it requires.
There has a been a wide debate for many, many years, nearly since the discovery of protein on a molecular level, about how much protein we actually need in order to survive. The requirement for protein varies on an individual level, determined primarily on an individual’s activity level. For example, a sedentary individual requires much less protein than an athlete, as the athlete is more frequently breaking down tissue in need of repair. Largely, trial and error are required to determine how much protein you need, and from what sources your body best derives and assimilates them from.