How to determine protein quality in your diet

What is protein & why is it important for the body?

Did you know that the human body is comprised of about 16 per cent protein[1]? Proteins are complex molecules which are required for the structure, function, and regulation of the body’s tissues and organs[2].

The functions of protein in the human body are grouped into five categories[3]:

  1. Structural: protein forms the main components in hair, skin, muscles and most other organs and tissues.
  2. Biochemical: either aided with or without enzymes, biochemical reactions turn food into energy and provide a sense of satiety. Protein also aids breathing, digestion and nervous system functions/transportation.
  3. Hormonal: some hormones are proteins, and change throughout life from childhood to the later stages of life.
  4. Cell division: proteins regulate cell division, to replenish dead or damaged cells
  5. Immune system: antibodies are part of the immune system, which fight infections.

Not all protein is created equal

Long chains of amino acids are the building blocks of protein, which can be broken down into 2 categories.

  • Non-essential amino acids: these 11 are produced by the body. The term “non-essential” is potentially misleading, as all amino acids play important structural and functional roles in the body.
  • Essential amino acids: the remaining 9 must be consumed from food. Foods which contain all 9 essential amino acids are “complete proteins”, while those lacking sufficient quantities of 1 or more of the essential amino acids are “incomplete proteins”. Foods with incomplete proteins can be combined together to form a complete protein source.
  • Complete protein food sources: meat, fish, dairy, eggs & soy.
  • Incomplete protein food sources: nuts/seeds, legumes, grains, vegetables.

Complete and incomplete proteins can be further examined and ranked by their quality. Protein quality is determined by either PDCAAS (protein digestibility-corrected amino acid score) or DIAAS (digestible indispensable amino acid score). Both of these scores were created by the Food and Agriculture Organization of United Nations (FAO), and it is their recommendation that DIAAS be used as the preferred method[4].

The DIAAS uses a mathematic equation to calculate the “individual indispensable amino acids in the dietary protein relative to human reference amino acid requirement pattern” [5]. Foods are then assigned a score, and ranked. Unlike DIAAS, PDCAAS truncates values to 1, so it isn’t able to account for minor variations like DIAAS[6].

How much is enough protein to consume?


The Australian and New Zealand governments created the Nutrient Reference Values based on currently available scientific knowledge[7]. The research body lists the EAR (estimated average requirement) and RDI (recommended dietary intake) for adults.

Even distribution & higher protein consumption

Recent research into the timing and consumption of protein suggests that even distribution throughout the day, with 25g-30g at each meal, can maximize muscle protein synthesis[8]. This amount of protein is significantly greater than the current RDI for women.

This study is of particular interest to older adults who are encouraged to consume considerably higher than the minimum protein requirements for optimal health[9]. The EAR and RDI do not “account for the compensatory loss of muscle mass”9 or lower rates of protein synthesis in older adults.

An increase in dietary protein for older adults has shown to increase lean mass gain, when combined with resistance exercise. 40 per cent of Australians in their 70s experienced a fall in the past 12 months[10]. An increase in lean muscle mass from dietary protein and resistance exercise has been found to reduce the incidence of falls among this cohort[11].












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