Essential, in more ways than one.

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