Nutrient profile | Proteins
Essential, in more ways than one.
Image credit: Daniella Witte via Pella Hedeby in Residence Magazine
Nutrient type Macronutrient
Overview Dietary proteins are composed of long polypeptide chains, which are digested to form smaller peptides and, eventually, single amino acids - ‘building blocks’ - that the body uses to produce its own proteins [1]. Of the 20 common amino acids, nine are known as essential amino acids, which cannot be sufficiently synthesised by the body and therefore must be obtained from the diet [1]. The remaining 11 are non-essential amino acids, and can usually be produced by the body if dietary intake is inadequate [1]. With an estimated 30,000 unique proteins found within the body - each supporting vital functions including tissue growth and repair, energy production, detoxification, nutrient transportation, and hormone and immune activity - consuming adequate amounts of dietary protein is critical, even for those of us who aren’t embarking on intensive training regimes in the gym [1; 2].
Rich food sources
High-quality protein may be sourced from animals or plants [1]. In general, animal-derived proteins (including lean meat, fish and other seafood, poultry, dairy products and eggs) are complete proteins and therefore contain all nine essential amino acids, unlike most plant-derived proteins [1]. Quinoa, soy products (e.g. tofu, tempeh, soy milk), spirulina and hemp seeds are all examples of complete plant-derived proteins; however, specific combinations - ideally within the same meal, otherwise over the course of a day - of other plant proteins such as legumes, nuts and seeds will also achieve a complete amino acid profile [1; 2].
Generally speaking, the following, complementary plant-derived protein sources may be combined to obtain all nine essential amino acids:
Legumes (e.g. lentils, chickpeas) + whole grains (e.g. oats, brown rice)
Legumes + nuts and seeds (e.g. pumpkin seeds, sunflower seeds) [2].
Functions and benefits
Tissue growth, repair and maintenance. Proteins are vital components of most body structures, especially muscle, skin and connective tissue, and are needed to replace dead or damaged cells [1; 2].
Energy production and metabolism. Proteins facilitate many biochemical reactions and metabolic processes in the body, including digestion and energy production [3]. Each gram of protein provides 17 kJ of energy [2].
Transportation of oxygen and nutrients. Certain proteins transport oxygen and other nutrients around the body, via the bloodstream; for example, haemoglobin transports oxygen, and transferrin transports iron. Other proteins within cellular membranes enable the movement of substances in and out of cells [1].
Hormone synthesis. Some amino acids - including tyrosine and tryptophan - support the synthesis of essential hormones and neurotransmitters including thyroid hormones, dopamine, epinephrine (adrenaline), norepinephrine (noradrenaline) and melatonin [3]. Meanwhile, other hormones - including insulin, growth hormone and antidiuretic hormone - are derived from peptides [3].
Detoxification and antioxidant activity. Glutathione, the primary antioxidant produced by the body (rather than obtained from foods,) is derived from peptides; it helps defend the body against oxidative damage caused by environmental toxins, supporting detoxification and also the body’s inflammatory responses [2; 3].
Immune activity. Proteins support the formation of white blood cells, antibodies and other immune proteins that defend the body against pathogens and disease [1].
pH and fluid balance. Proteins also influence the balance of blood and other fluids in the body; certain amino acids also help to neutralise or buffer fluid pH, helping to maintain the delicate acid-base balance in the body [1; 2].
Storage in the body The body is unable to store protein, meaning amino acids must be replenished daily [1; 2]. Protein that exceeds the body’s requirements is converted to either glucose (to be stored as glycogen) or ketone bodies (to be stored as fat) [1].
Signs and symptoms of inadequate protein intake A mild to moderate protein deficiency may result in low energy, frequent illness, brittle, thinning hair and nails, poor posture and/or muscle tone, and anaemia [2].
Recommended protein intake
Dietary guidelines suggest that 15-25 per cent of an individual’s daily energy requirements are met by protein [2].
Recommended dietary intake (RDI) | Protein
Women:
19-70 years: 0.75 g/kg of body weight, per day
70+ years: 0.94 g/kg of body weight, per day
Men:
19-70 years: 0.84 g/kg of body weight, per day
70+ years: 1.07g/kg of body weight, per day
Children:
Girls: 1.08 g/kg of body weight, per day (1-3 years); 0.91 g/kg of body weight, per day (4-8 years); 0.87 g/kg of body weight, per day (9-13 years); 0.77 g/kg of body weight, per day (14-18 years)
Boys: 1.08 g/kg of body weight, per day (1-3 years); 0.91 g/kg of body weight, per day (4-8 years); 0.94 g/kg of body weight, per day (9-13 years); 0.99 g/kg of body weight, per day (14-18 years) [4].
Note. Recommended dietary intake (RDI) refers to average amount of a nutrient needed each day to meet the nutritional needs of almost all healthy individuals within a particular demographic [5]. As such, an individual’s demand for a particular nutrient may extend beyond the RDI, depending on their energy requirements.
Indicative (approximate) serving sizes - examples only
1 fillet (~150 g) of grilled salmon provides 34 g protein
100 g grilled chicken breast provides 30 g protein
150 g firm tofu provides 19 g protein
2 large organic eggs provide 11 g protein
1 cup of soy milk provides 9 g protein
1 cup of cooked quinoa provides 7 g protein
Half a cup of natural yoghurt provides 6 g protein
1 tablespoon of hemp seeds provides 3 g protein
2 teaspoons of powdered spirulina provides 3 g protein [6].
Recipes to try | Complete protein sources
Miso glazed salmon with quinoa, broccolini + avocado, by Jacqueline Alwill (@brownpapernutrition)
Cypriot salad my way, by Jacqueline Alwill (@brownpapernutrition)
Tip. Further boost protein content by serving this salad alongside a complete protein such as grilled chicken, eggs or tofu.
Other notes
Alongside whole food protein sources, protein powders offer an incredibly convenient protein boost - it’s important though to choose one without unnecessary additives, especially if it’s part of your daily diet.
Whey protein isolate (WPI) formulas contain approximately 90% protein and very little lactose, and are therefore well-tolerated by those who are lactose intolerant; meanwhile, both lactose and fat content are higher in whey protein concentrate (WPC) formulas [7]. For these reasons, I like The Healthy Chef Pure Native WPI and Bare Blends Bare Whey Protein Isolate.
Meanwhile, for those of us unable to consume animal products or who are particularly sensitive to dairy (or who simply prefer a plant-based option), many sophisticated plant-based formulas - without the trademark gritty, grainy texture - are now available. I love The Beauty Chef Body Inner Beauty Support powder and Bare Blends Bare Plant Protein.
The RDI for protein increases with increased energy requirements, including those associated with pregnancy and breastfeeding [4].
References.
[1] Whitney, E., Rolfes, S., Crowe, T., & Walsh, A. (2019). Understanding nutrition (4th ed.). Cengage Learning Australia Pty Limited.
[2] Paxton, F. (2015). Foundations of naturopathic nutrition: A comprehensive guide to essential nutrients and nutritional bioactives. Routledge.
[3] Gropper, S. S., Smith, J. L., & Carr, T. P. (2022). Advanced nutrition and human metabolism (8th ed.). Cengage Learning, Inc.
[4] Australian National Health and Medical Research Council [NHMRC] and New Zealand Ministry of Health [NZMoH]. (2019). Protein. Nutrient Reference Values for Australia and New Zealand. Retrieved August 17, 2022, from https://www.nrv.gov.au/nutrients/protein
[5] NHMRC and NZMoH. (2017). Introduction. Nutrient Reference Values for Australia and New Zealand. Retrieved August 17, 2022, from https://www.nrv.gov.au/introduction
[6] Food Standards Australia and New Zealand. (2021). Australian Food Composition Database. https://www.foodstandards.gov.au/science/monitoringnutrients/afcd/Pages/default.aspx
[7] Rashmi, K., Gupta, M., Tarapdar, S., Duggal, M., Tyagi, S., Kaur, H., Vyas, P., & Gupta, A. (2022). Influence of dietary molecules on human health: Whey proteins. Research Journal of Pharmacy and Technology, 15(4), 1910-1914. https://doi.org/10.52711/0974-360X.2022.00318