Before we dive into Protein, I would like to briefly discuss what Macronutrients are in slightly more detail. I have referred to them in my first article “What is Good Nutrition?” and will use that term throughout the many nutrition articles I write, so I feel it is best to provide a brief definition/description to ensure understanding.
Macronutrients and Micronutrients
Macro means large, long.
Micro means small.
Nutrient is defined as a substance that provides nourishment essential for growth and the maintenance of life.
So we have Macronutrients such as Proteins, Carbohydrates, and Fats and Micronutrients, such as Vitamins and Minerals. Since Proteins, Carbohydrates, and Fats make up a larger proportion of our dietary intake, more so than Vitamins and Minerals (Micronutrients) do, they are given the Prefix Macro. We do not consume Vitamins & Minerals in pound quantities, but instead milligram and microgram quantities, thus Micro.
Moving forward I will simply refer to them as such and not bore you with their definitions.
Protein plays a number of important roles in our our health and wellbeing. Protein is essential and there can be confusion when it comes to how much protein one requires depending on their age and lifestyle and where we can/should obtain protein. Due to the amount of information that will be covered on protein this article will be divided into Three Parts.
Protein is an essential nutrient that our bodies require. Specifically, proteins are composed of amino acids, which our bodies utilize. These various amino acids play essential roles in our physiology. We have essential and nonessential amino acids.
Essential or Indispensable refers to amino acids that our bodies cannot make, but instead need to be supplied exogenously, (supplied from outside of the body) in this case from the food we eat. Whereas Nonessential or Dispensable amino acids can be synthesized within our bodies from other amino acids. Lastly, we also have what are called Conditionally Indispensable Amino Acids. These can be synthesized from other amino acids, but in the case of illness or organ failure, these amino acids can become Essential or Indispensable. (Gropper & Smith, 2013, pg. 186)
So, when we say sources of Proteins, we are really referring to sources of amino acids.
What is the structure of an Amino Acid?
It contains a Central Carbon (C), at least one amino group (–NH2), at least one carboxyl (acid) group (–COOH), and a side chain (R group) (Gropper & Smith, 2013, pg. 183). What separates Proteins from Carbohydrates and Fats/Lipids is the Nitrogen (N) in their Chemical Structure.
As we have learned, Protein is an essential macronutrient due the Essential/Indispensable Amino Acids our bodies require for us to consume through our diet.
But what exactly are these amino acids doing in our bodies?
What does this all mean?
Proteins are responsible for enzymatic reactions, which are necessary for us to sustain life. Some act as hormones, hormones being chemical messengers within our bodies. (Gropper & Smith, 2013, pg. 211 – 212)
Contractile and fibrous proteins are throughout the body and play a structural role. Contractile proteins make up our skeletal, cardiac and smooth muscles while fibrous protein include collagen, elastin, and keratin. The fibrous proteins are found in bone, teeth, skin, tendons, cartilage, blood vessels, hair and nails. (Gropper & Smith, 2013, pg. 212 – 213)
Proteins play a role in acid-base balance through acting as buffers within the body. Protein’s presence in the blood and cells allows them to influence fluid balance because they attract and keep water within a particular area. (Gropper & Smith, 2013, pg. 213)
Immunoglobulins (Ig) or antibodies (Ab) are a group of proteins called immunoproteins which are vital to our defense against viruses and/or bacteria that have entered our bodies. (Gropper & Smith, 2013, pg. 213)
Transport proteins are found within the cell membranes of our cells controlling what enters and exits the cell and others, like Albumin, are found within the blood and transport nutrients and minerals throughout the body. (Gropper & Smith, 2013, pg. 214)
Lastly, in the case of a sudden, critical illness, acute phase reactant proteins respond to infection, injuries or inflammation. These acute phase reactant proteins stimulate our immune system, promote wound healing, and chelating and removing free iron that bacteria could use for further growth. (Gropper & Smith, 2013, pg. 214 – 215)
As I mentioned above, what makes protein/amino acids different from the other macronutrients is the fact that it possesses a nitrogen (N) molecule within its chemical structure. Our bodies utilize amino acids to synthesis Nitrogen-Containing Compounds.
These nitrogen containing compounds are not proteins, but, as you will see, are very important. These compounds are:
This is a tripeptide (derived from three amino acids — glycine, cysteine, and glutamate) that plays the role as a major antioxidant, capable of scavenging free radicals, protecting critical components of our cells, and preventing oxidation of SH-containing proteins. Glutathione is responsible for many other reactions and functions, but one can remember it as a primary antioxidant in our physiology.
The synthesis, or production, of glutathione is sensitive to protein intake, so if one is consuming inadequate amounts of protein they will have decreased concentrations throughout their body. Decreased concentrations of glutathione negatively impacts our bodies. You can find reduced glutathione in foods such as meat, vegetables and fruits. However, consuming optimal quantities of protein, in order to ensure adequate glycine, cysteine, and glutamate concentrations is still important. (Gropper & Smith, 2013, pg. 216) While all three amino acids are required, a rich source of glycine can be found in collagenous cuts of meat (i.e., briskets, chuck roasts, oxtail, chicken with skin and tendons, chicken feet, even collagen powder).
Carnitine is another nitrogen-containing compound, but it is synthesized from the amino acid lysine. Carnitine is found is most body tissues, and is responsible for transporting fatty acids to be oxidized for energy within our mitochondria. In addition to fatty acid metabolism, carnitine is required to obtain energy from ketones. Without carnitine, one would have impaired energy metabolism.
While carnitine can be synthesized within our bodies (in the liver and kidneys), we can also obtain it from foods like beef and pork. (Gropper & Smith, 2013, pg. 216 – 217)
While you may not have been familiar with Glutathione or Carnitine, one has most likely heard of Creatine, especially if you have a background in lifting weights or sports. Like carnitine, creatine and can be synthesized from three amino acids (glycine, arginine, and methionine) or obtained from foods. (Gropper & Smith, 2013, pg. 217 – 219)
Creatine is responsible for providing immediate energy to tissues with a high energy demand, such as the muscles and brain. While creatine can be produced endogenously (within our bodies), it may be best to get it from our diets through eating meat and fish. If one is not consuming meat and fish, in the case of vegans and vegetarians, it may be best to supplement. Oral supplementation with 5g of creatine monohydrate was actually found to improve brain function in vegans and vegetarians.
Creatine intake and body stores may be more important the older one becomes. This is because muscle mass declines as one ages, and creatine, with or without resistance training, has been shown to aid in preservation of muscle function and lean mass. While there appears to be promise in the role of creatine supplementation in preservation of bone and mental cognition in the aging population, further research is required.
Carnosine, made from the amino acid histidine and beta-alanine, plays many crucial role within our bodies. While we can synthesize it, we can also obtain it through our diet by eating meat. Carnosine functions as an antioxidant within the cell, a chelator for toxic metal ions, a buffer, and an inhibitor of non-enzymic glycosylation of proteins. (Gropper & Smith, 2013, pg. 219) Lastly, in vitro, carnosine has been seen to reverse the normal symptoms of cell senescence (biological aging).
The last nitrogen-containing nonprotein compound we will discuss is choline. Choline is made within our bodies through the methylation of the amino acid serine using SAM (S-adenosyl methionine). (Gropper & Smith, 2013, pg. 219)
The best food sources of choline are found as part of the phospholipid lecithin (phosphatidylcholine). Such as eggs (lecithin is within the yolk) and liver. However, you can obtain choline from other foods such as:
Amounts for each food required to reach the AI (Adequate Intake) will vary. For example, around four eggs a day would provide close to the AI for men, while one would need to eat 3 lbs of beef or 1.75 lbs of beans (weighed dried) to obtain the equivalent amount of choline (Masterjohn, 2019).
All cells in our bodies are enclosed within a phospholipid bilayer. A major component of this fatty membrane is phosphatidylcholine, which, as you can see, is made from choline. The vehicles required to move fat out of our livers is composed of the same fatty membrane. If we do not have enough choline, this means not enough of these transport vehicles, thereby increasing one’s risk of fatty liver disease.
Finally, choline is used to synthesize acetylcholine, a neurotransmitter (Masterjohn, 2019). Acetylcholine’s functions are numerous. It is used to contract our muscles and activating our “rest & digest” mode. We use it to stay focused, learn and form memories, and allows us to get into REM sleep (Masterjohn, 2019).
You made it through Part 1 on the Importance of Proteins. You now understand how essential proteins are to our health and that they specifically provide our bodies with amino acids. Some of these amino acids are essential, while other are nonessential. These amino acids are used throughout our bodies to regulate hormones, build muscle and soft tissue, balance pH and fluid levels, transport nutrients, and fight and respond to infections and/or injuries. Then, just when you thought amino acids did enough directly, we discussed Nonprotein Compound’s indirect, yet vital, roles.
Up next is Part 2, where we will discuss Sources of Protein. Specifically, we will look at whether Plant vs. Animal sources of Protein differ in Quantity and Quality.
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Gropper, S.S. & Smith, J.K. (2013). Advanced Nutrition and Human Metabolism. Belmont, CA: Wadsworth.
Masterjohn, C. (2019). Vitamins and Minerals 101.