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Protein is what’s referred to as a macronutrient.  The other macronutrients are carbohydrate, lipids (fat) and water.  Protein is different from carbohydrate and lipids because it contains carbon, hydrogen, oxygen and nitrogen, whereas carbohydrate and lipids only contain carbon, hydrogen and oxygen.

Protein

 A macronutrient needs to be taken into the body in large amounts, usually measure in grams.  Micronutrients are vitamins and minerals.  They are no less important than macronutrients, they are just required in smaller amounts (micrograms (mg) or milligrams (µg)). 

Protein is made up of amino acids, these are known as the building blocks of proteins.  The term ‘building blocks’ is very appropriate as proteins main role in the body is growing, repairing and replacing tissues.  There are 20 different types of amino acids (like 20 different types of blocks), with different chemical structures (made from different materials).  The body can make approximately half of these itself, but the rest must be ingested from food.  They are known as ‘essential amino acids’, there are 9 know essential amino acids.  The different amino acids join in chains with different lengths, sequences and shapes depending on what they are being used for in the body. 

Enough about what proteins are made up of, what do they do aside from their structural role of growth, repair and maintenance of cells?  The answer is quite a lot!  Proteins have many functions compared to carbohydrate and fat.  Most importantly, these functions can only be carried out by protein, no other nutrient can fill in if there isn’t enough protein.

  1. Protein is used by the body for growth, repair and maintenance of the billions of cells that make up our bodies.  These proteins are constantly breaking down and regenerating.  Usually your body breaks down the same amount of protein it needs to build and repair cells, but it exceptional circumstances such as when you’re ill or after a major surgery, pregnant or breastfeeding, after strenuous exercises and if you are elderly, the body breaks down more protein than it can replace, which increases your body’s protein requirement (Van De Walle, 2018). 
  1. Proteins make up most of our body’s hormones which act as chemical messengers.  They are secreted from glands and carry messages in the blood to the target organ or tissue where they bind to protein receptors on the surface of the cell (Van De Walle, 2018).  Some hormones you may have heard of that are composed of proteins are Insulin: Signals the uptake of glucose or sugar into the cell.  Glucagon: Signals the breakdown of stored glucose in the liver.  hGH (human growth hormone): Stimulates the growth of various tissues, including bone.  ADH (antidiuretic hormone): Signals the kidneys to reabsorb water.  ACTH (adrenocorticotropic hormone): Stimulates the release of cortisol, a key factor in metabolism (Cooper, 2000a). 
  2. Proteins play a role in immune function, they make up antibodies which attack and inactivate foreign bodies that could be potentially harmful to us, such as bacteria and viruses that can cause illness (Li et al., 2007; Schroeder and Cavacini, 2010).
  3. Enzymes are chemical catalysts.  A catalyst is a substance that speeds up a reaction but isn’t used up in the reaction itself (Cooper, 2000b).  All enzymes are proteins.   In the digestion process amylase is an enzyme used to breakdown carbohydrate, protease as the enzyme used to breakdown protein and lipase is the enzyme used to breakdown lipids.  Without these enzymes our body would not be able to digest and absorb the nutrients we need to live.  Enzymes also play an important role in energy production, blood clotting and muscle contraction (Martínez Cuesta et al., 2015).
  4. Protein acts as a buffer to ensure the pH of the blood and other bodily fluids (how acidic or basic it is) (Hamm et al., 2015; Lamanda et al., 2007).  The pH is measured on a pH scale which goes from 0, which is the most acidic, to 14, which is the most basic.   If the blood becomes to acidic or too basic this could lead to coma or death.  The blood should be a neutral 7.4 at all times (Van De Walle, 2018).
  5. Some proteins transport nutrients and other substances around the body, while other proteins store them (Van De Walle, 2018).  Vitamins, minerals, blood sugar, oxygen and cholesterol are all transported around the body by proteins (Levy et al., 2007; Seetharam and Yammani, 2003; Hashimoto and Kambe, 2015).  Haemoglobin is the protein that transports oxygen around the body to your lungs and body tissues, it is found in the red blood cells.  Low haemoglobin levels can lead to anaemia (Van De Walle, 2018).  Lipoproteins transport cholesterol in the blood and glucose transporters move sugar into your cells where it is needed for energy (Van De Walle, 2018).   
  6. Proteins in the blood are involved in fluid balance, they ensure the correct amount and type of fluid is in the correct compartment of the body.  Albumin and Globulin are two proteins that ensure the correct volume of fluid is in the blood by attracting and secreting fluid as needed (Busher, 1990; Hankins, 2006).  Kwashiorkor is a form of protein deficiency which occurs when a person’s overall calorie intake is enough, but they are not getting enough protein.  Is is most common in 3rd world countries where diets are high in starchy foods and very low in protein,   Symptoms include failure to thrive, fluid build-up causing swelling and oedema especially around the stomach area, hair colour loss, skin becomes patchy, thickened and scaly and muscles waste away  (G. Coulthard, 2015; Heikens and Manary, 2009). 
  7. Finally, Protein can be used for energy in exceptional circumstance when there isn’t enough fat or carbohydrate available.  This is less than ideal because basically your body must break down muscle to use protein as energy (Carbone et al., 2014; Berg et al., 2002).  This process is called gluconeogenesis and it means making glucose form non-carbohydrates.  Carbohydrate and fats should be used for energy; this is their main function.  To use protein for energy the body has to work a lot harder (Rui, 2014). 

All those essential functions carried out by protein just show you how important it is.  Now we’ll look at different protein sources.  You can get protein from plant and animal sources.  Animal sources usually contain higher amounts of protein than plant foods, the exception being soya.  Animal sources also contain all 9 essential amino acids, while plant food may lack significant amounts of a few.  However, if you are vegan or vegetarian it is still possibly to get all your essential amino acids, you just must pair certain plant foods together.  For example, baked beans are lacking the essential amino acid lysine, but they are high in methionine.  Bread (toast) is low in lysine and high in methionine.  When eaten together as the classic beans on toast, you get a complete protein!  Below is a table showing good sources of protein, both plant and animal sources.

AnimalPlant
Poultry
Fish and shellfish
Lean red meat
Eggs
Dairy
Soya products
Nuts, especially almonds but peanuts, pistachios and cashews are also good
Oats
Broccoli
Lentils
Beans (baked beans, soybeans, chickpeas, kidney beans etc.)
Quinoa
Seeds
Brussel sprouts
Ezekial bread

(Gunnars, 2020)

Although animal protein foods are of high biological value (they contain all essential amino acids), they can be high on saturated fat.  Plant sources are of low biological value (they don’t contain all the essential amino acids), but they are low in fat and when you combine certain plant foods, they can make up a complete protein.  There is a common misconception that in order to increase muscle mass you must eat a lot of meat but think about our close relatives Gorillas.  I don’t know about you, but I wouldn’t want to be in a fight with a Gorilla!  Their diets are 100% plant based.  Some well known athletes also follow a vegan diet (Top 10 Most Successful Vegan Athletes, 2018).

  • Venus Williams – Tennis player
  • Tony Gonzalez – NFL player
  • David Haye – Boxer
  • Nate Diaz – UFC fighter
  • Heather Mills – Skier
  • Kendrick Farris – Weightlifter
  • Scott Jurek – Long distance runner
  • Jermain Defoe – Football player
  • Patrick Baboumian – Body builder 
  • Lewis Hamilton – Formula one driver

Protein supplements have become very popular in recent years for both professional athletes and the general public.  They are being used as meal replacements and for weight loss.  They have alleged health benefits which have unfortunately led to overuse in both teenagers and adults (Health Risks of Protein Drinks – Consumer Reports, 2010).   The protein supplement market in a multi-billion dollar industry (Samal and Samal, 2018).  A study was carried out on 15 different protein supplements.  The supplements were sent to an outside lab for analysis to find out if they contained any toxic compounds.  Results showed that 8 out of 15 of the supplements contained levels of lead that would require a warning notice in California under law (Health Risks of Protein Drinks – Consumer Reports, 2010).  If you are using protein supplements you need to be extremely careful where you source them.  Unlike food and medication, in the USA nutritional supplements such as protein powders and protein supplements are not regulated by the FDA to ensure they do what they say they are going to do, or even if they are safe for human consumption.  There is also no legal requirement that supplements be tested to make sure they contain what the labels say they contain. Studies have shown that many dietary supplements sold in major drug store chains, health food stores, and respected online outlets.  do not contain what they are supposed to or contain potentially harmful ingredients not listed on the label (Hirschfield, 2018).  However, since 2002 food supplements have been regulated in the EU under the Food Supplements Directive 2002/46/EC (Coppen, 2018).  A food supplement is defined as “foodstuffs the purpose of which is to supplement the normal diet and which are concentrated sources of nutrients or other substances with a nutritional or physiological effect, alone or in combination, marketed in dose form, namely forms such as capsules, pastilles, tablets, pills and other similar forms, sachets of powder, ampoules of liquids, drop dispensing bottles, and other similar forms of liquids and powders designed to be taken in measured small unit quantities.”  This directive covers;

  • general requirements for food safety, responsibilities for producers and obligations for traceability, information provision and recall of harmful products (Regulation (EC) No 178/2002)2
  • preparation and hygiene of foodstuffs based on the principles of Hazard Analysis and Critical Control Points (HACCP) (Regulation (EC) 852/2004)
  • food labelling with the aim of adequately informing the consumer about the composition, properties and use of foodstuffs (Regulation (EU) 1169/2011)
  • use of nutrition and health claims, which must be authorized before they can be used (Regulation (EC) 1924/2006)
  • conditions for the use of additives (Regulation (EC) 1333/2008)
  • maximum levels for residues and contaminants (Regulation (EC) 369/2005 – Regulation (EC) 1881/2006)
  • approval of novel foods and food ingredients not on the European market before 15 May 1997 (Regulation (EU) 2015/2283)

As mentioned above, not enough protein in the diet can lead to conditions such as Kwashiorkor.  It can also lead to stunted growth in children.  Muscle wasting including the heart.  Weakened immune system.  Poor wound healing, Anaemia due to fewer red blood cells or less than normal quantity of haemoglobin in the red blood cells.  Oedema, Fatty infiltration of the liver due to its inability to be transported from the liver.  You’ll notice all these symptoms correspond to proteins essential functions.  The amount of protein you require depends on your age and gender.  The average adult needs approximately 0.8g of protein for every kilo they weigh.  Below is a table showing how much protein different ages and genders require.  Notice how growing children and pregnant/lactating women require a lot more.

Table 1: Recommended amounts of protein depending on age and gender (Dietary Reference Values | DRV Finder, 2017)

Protein deficiency in developed countries is almost unheard of.  Western diets get more than enough protein easily from our food, no need to add extra with supplements in my honest opinion.  At least if you’re getting it for good quality foods you can be sure you’re not putting nasty chemicals in your body which as of now may be deemed as safe, but the long-term effects still aren’t known for sure.  Like anything, too much can nearly be as bad as too little.  A long-term high protein diet has been shown to have some long-term adverse health effects such as;

  • Disorders of the bone
  • Calcium homeostasis
  • Disorders of renal function
  • Increased cancer risk
  • Disorders of the liver
  • Progression of coronary artery disease (Delimaris, 2013)

In conclusion, I feel people should be able to get enough protein from food sources regardless of whether they are vegan/vegetarian or not.  If you do need to take protein supplements be careful where you source them.  You should get a registered dietician or medical professional to recommend what kind and how much to take.  Choose healthy protein sources that are low in saturated fat.

References

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Busher, J.T. (1990) Serum Albumin and Globulin. In: H.K. Walker, W.D. Hall, and J.W. Hurst (eds.) Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition Boston: Butterworths,.

Carbone, J.W., Pasiakos, S.M., Vislocky, L.M., Anderson, J.M. and Rodriguez, N.R. (2014) Effects of short-term energy deficit on muscle protein breakdown and intramuscular proteolysis in normal-weight young adults. Applied Physiology, Nutrition, and Metabolism = Physiologie Appliquee, Nutrition Et Metabolisme, 39(8) 960–968.

Cooper, G.M. (2000a) Signaling Molecules and Their Receptors. The Cell: A Molecular Approach. 2nd edition, Available from https://www.ncbi.nlm.nih.gov/books/NBK9924/ [accessed 19 November 2020].

Cooper, G.M. (2000b) The Central Role of Enzymes as Biological Catalysts. The Cell: A Molecular Approach. 2nd edition, Available from https://www.ncbi.nlm.nih.gov/books/NBK9921/ [accessed 19 November 2020].

Coppen, P. (2018) Food Supplements in the European Union: the Difficult Route to Harmonization Available from https://www.raps.org/news-and-articles/news-articles/2018/7/food-supplements-in-the-european-union-the-diffic [accessed 19 November 2020].

Delimaris, I. (2013) Adverse Effects Associated with Protein Intake above the Recommended Dietary Allowance for Adults Available from https://www.hindawi.com/journals/isrn/2013/126929/ [accessed 19 November 2020].

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G. Coulthard, M. (2015) Oedema in kwashiorkor is caused by hypoalbuminaemia. Paediatrics and International Child Health, 35(2) 83–89. Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4462841/ [accessed 19 November 2020].

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Hamm, L.L., Nakhoul, N. and Hering-Smith, K.S. (2015) Acid-Base Homeostasis. Clinical Journal of the American Society of Nephrology : CJASN, 10(12) 2232–2242. Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4670772/ [accessed 19 November 2020].

Hankins, J. (2006) The role of albumin in fluid and electrolyte balance. Journal of Infusion Nursing: The Official Publication of the Infusion Nurses Society, 29(5) 260–265.

Hashimoto, A. and Kambe, T. (2015) Mg, Zn and Cu Transport Proteins: A Brief Overview from Physiological and Molecular Perspectives. Journal of Nutritional Science and Vitaminology, 61 Suppl S116-118.

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Heikens, G.T. and Manary, M. (2009) 75 years of Kwashiorkor if Africa. Malawi Medical Journal, 21(3) 96–100. Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3717488/ [accessed 19 November 2020].

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Lamanda, A., Cheaib, Z., Turgut, M.D. and Lussi, A. (2007) Protein Buffering in Model Systems and in Whole Human Saliva. PLoS ONE, 2(2). Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1803027/ [accessed 19 November 2020].

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Li, P., Yin, Y.-L., Li, D., Kim, S.W. and Wu, G. (2007) Amino acids and immune function. The British Journal of Nutrition, 98(2) 237–252.

Martínez Cuesta, S., Rahman, S.A., Furnham, N. and Thornton, J.M. (2015) The Classification and Evolution of Enzyme Function. Biophysical Journal, 109(6) 1082–1086. Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4576142/ [accessed 19 November 2020].

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Samal, J.R.K. and Samal, I.R. (2018) Protein Supplements: Pros and Cons. Journal of Dietary Supplements, 15(3) 365–371. Available from https://www.tandfonline.com/doi/full/10.1080/19390211.2017.1353567 [accessed 19 November 2020].

Schroeder, H.W. and Cavacini, L. (2010) Structure and Function of Immunoglobulins. The Journal of allergy and clinical immunology, 125(2 0 2) S41–S52. Available from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3670108/ [accessed 19 November 2020].

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