Protein
Photo by Aamulya
Proteins are an essential component for every single cell, tissue, and process in our bodies. So let’s take a step back and return to basics to look at what proteins are and what are their functions.
What are proteins?
Proteins are one of the three macronutrients found in our food - the others being carbs and fats. They are essential nutrients that we need to survive, come in many different shapes and sizes, and are found throughout our entire bodies - in muscles, bones, skin, hair, etc.
Proteins are made of many different amino acids - building blocks - linked together. There are 20 different amino acids found in plants and animals which are classified as either essential or non-essential.
Essential amino acids - cannot be produced by our bodies and need to come from our diet. There are 9 essential amino acids.
Non-essential amino acids - can be produced by our bodies and do not need to come from our diet. There are 11 non-essential amino acids.
The specific amount and sequence - how they are arranged - of amino acids are unique to each protein and determine the shape and function of that protein.
Unlike carbohydrates and fats, we do not have a significant reserve of body protein to use as a source of energy, therefore we need regular “top-ups” to avoid depleting our bodies of proteins.
Why do we need protein?
Proteins are the building blocks of our bodies and the structural component of all living cells and tissues as well as many enzymes & hormones. Essentially proteins play a role in everything - in every single process, in every single cell of our bodies.
Among these processes, proteins are involved in:
Body growth and repair - proteins help repair muscle, skin & other body tissues, and are particularly important during times of rapid growth - childhood & adolescence - or increased demand - pregnancy, breastfeeding & physical stress like exercise.
Carrying substances - proteins move essential molecules around our bodies, for instance, haemoglobin - a protein contained in red blood cells - delivers oxygen around our bodies.
Metabolism - digestive enzymes are proteins which help facilitate chemical reactions and are crucial to digest food.
Supporting immune protection - proteins make up our antibodies - the protective proteins produced by our immune system - to help us fight infections.
Blood sugar control - insulin is a hormone made of proteins which controls our blood sugar levels by helping our cells absorb sugar.
Movement - proteins found in muscles allow and support muscle contraction in order for us to move.
Providing a source of energy - proteins can be a source of energy for our bodies with 1 gram of protein providing 4 calories (kcals). However, proteins are not the preferred source of energy as they are invaluable for many other processes.
Additionally, it has been shown that protein-rich food promotes satiety - feeling of fullness - more than foods high in carbohydrates or fats.
How much protein?
Proteins are continuously in a state of turnover, whereby our bodies break down protein from our food into amino acids to make other proteins - protein synthesis. This means we consistently need to eat dietary protein to supply our bodies with amino acids and ensure the turnover continues.
The amount of protein we need depends on our age, sex, health and level of physical activity, with increases in periods of growth - childhood -, pregnancy, and breastfeeding.
Infants, children and adolescents - 0.83g to 1.31g per kg of body weight per day depending on age.
Adults (including older adults) - 0.83g per kg of body weight per day.
Pregnant women - additional intake of:
1g per day for the 1st trimester
9g per day for the 2nd trimester
28g per day for the 3rd trimester.
Breastfeeding women - additional intake of:
19g per day during the first 6 months of lactation
13g per day thereafter.
In other words, a 70kg adult should be aiming to eat at least 58g of protein every day - this is the amount of protein you can find in 200g of chicken, 220g of salmon or 2 cups of tofu.
What foods contain protein?
All foods contain some protein, but the amount and quality vary widely.
Proteins can be classified by ‘quality’ based on the amount of amino acids they contain, particularly essential amino acids. Protein from animal sources are often referred to as high-quality or ‘complete’ proteins as they contain the full range of essential amino acids to fulfill our bodies’ protein requirements, whereas plant foods may not provide all or have limited amounts of essential amino acids.
Even so, plant-based protein from a variety of foods - eaten during a day - can supply enough of all the essential amino acids - variety is key.
Some high-protein food sources include:
*Consuming high amounts of red & processed meat is associated with an increased risk of certain cancers. The World Cancer Research Fund (WCRF) recommends consuming no more than 3 portions of red meat per week (~ 350-500g cooked weight) and very little, if any, processed meat.
How much protein is in foods?
Generally, a portion of protein should fit into the palm of your hand. The table below shows the amount of protein found in an average portion of common animal and plant-based protein-rich foods:
Vegetarian and Vegan considerations
As previously mentioned protein ‘quality’ varies based on the amount of essential amino acids they contain, and the quality of plant-based proteins is usually lower than animal-based proteins.
However, a plant-based diet can provide enough protein if planned correctly.
Some plants do contain high-quality protein - for example soy -, and including a variety of plant-based protein - pulses, whole grains, nuts & soy products - throughout the day helps us to combine and complement the different amino acids to create complete forms of protein - containing all essential amino acids.
What’s the take-home?
Proteins are the building blocks of our bodies and essential nutrients that we need to survive.
Proteins are made of different combinations of amino acids which are categorised as either essential amino acids - which need to come from our diet - or non-essential amino acids - which can be produced by the body.
We need regular “top-ups” to avoid depleting our bodies of protein as they are involved in everything - body growth & repair, metabolism, immunity, etc.
We should be aiming to get 0.83g of protein per kg of our body weight per day - approximately 58g for a 70kg adult - which we can get from a variety of both plant-based or animal-based foods.
Vegetarians and vegans need to include a wide variety of plant-based proteins to ensure they are able to get the right amount of essential amino acids from their diet.
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References
British Nutrition Foundation. Healthy Sustainable Diets - Protein. 2021. Retrieved April 6, 2022, from https://www.nutrition.org.uk/healthy-sustainable-diets/protein/?level=Health%20professional
Leidy HJ, Clifton PM, Astrup A, Wycherley TP, Westerterp-Plantenga MS, Luscombe-Marsh ND, Woods SC, Mattes RD. The role of protein in weight loss and maintenance. The American Journal of Clinical Nutrition. 2015, 101(6), 1320S–1329S, https://doi.org/10.3945/ajcn.114.084038
European Food and Information Council (EUFIC). What’s in food - What are proteins and what is their function in the body? 16 Dec. 2019. Retrieved April 6, 2022, from https://www.eufic.org/en/whats-in-food/article/what-are-proteins-and-what-is-their-function-in-the-body
EFSA (European Food Safety Authority). Scientific Opinion on Dietary Reference Values for Protein. Available at: . European Food Safety Authority. 2012; 10(2):2557. Retrieved April 6, 2022, from https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/j.efsa.2012.2557
EFSA (European Food Safety Authority). EFSA sets population reference intakes for population. 9 Feb. 2012. Retrieved April 7 2022, from https://www.efsa.europa.eu/en/press/news/120209#:~:text=According%20to%20collated%20national%20food,g%20per%20day%20for%20women).
European Food and Information Council (EUFIC). Cooking Plant-based: how to get enough protein. 5 Jan. 2022. Retrieved April 6, 2022, from https://www.eufic.org/en/images/uploads/files/PlantBased_FactSheet_FINAL.pdf
World Cancer Research Fund / American Institute for Cancer Research. Continuous Update Project Expert Report - Meat, fish and dairy products and the risk of cancer. 2018. Retrieved April 7 2022, from https://www.wcrf.org/dietandcancer/meat-fish-and-dairy/
British Nutrition Foundation. Your Balanced Diet - Get Portion Wise. Nov 2021. Retrieved April 7, 2022, from https://www.nutrition.org.uk/media/ohunys2u/your-balanced-diet_16pp_final_web.pdf
McCance & Widdowson. The Composition of Foods integrated dataset 2021. 2021. Retrieved April 7, 2022, from https://www.gov.uk/government/publications/composition-of-foods-integrated-dataset-cofid