Protein Bioavailability and Why You Should Ignore it (mostly)

Remember in GCSE food tech when they told you that vegetarians were at risk of protein deficiency unless they ALWAYS paired "incomplete" proteins together?

Sadly this concept has permeated popular culture and I've been seeing some well meaning but inaccurate Instagram posts rating the quality of proteins.

The higher the rating the better according to many.

While this may be true for elite athletes, for the majority this is just a distraction.

Protein Digestibility

Protein quality can be rated on The protein digestibility-corrected amino acid score (PDCAAS) or more recently digestible indispensable amino acid score (DiAAS).

One of the limitations of such scores is that they use animal models - rats and pigs. (yes they fed them meat in the tests!). Humans have a unique digestive system and microbiota which cannot be replicated in animal tests.

Another issue is that plant-based foods are not well represented in the DiAAS or PDCAAS. With plant-based diets increasing in popularity I believe this has to change.

In addition, when the protein in foods is estimated, the amount of nitrogen is used in the calculation. It is assumed that all proteins have a nitrogen concentration of 16%. In fact this varies in different foods and may confuse the picture when we use given values in dietary recommendation.

Limiting Amino Acids

Amino Acids are building blocks which make up proteins. Certain amino acids need to be consumed as they cannot be made in the body. If a food lacks an essential (sometimes called indispensable) amino acids, it can be described as incomplete or low biological value.

Those terms sound quite negative. However these incomplete proteins are not as useless as some may have us believe.

In addition, amino acids can be stored short term for use when needed.

Soy contains all the essential amino acids, while other plant sources may not. However if a range of foods is consumed throughout the day, this should not affect you negatively at all.

Animal sources of protein are likely to contain all of the essential amino acids, but are generally more calorie dense meaning that too mush may lead to weight gain.

Realistically we do not eat one single food all day every day. each meal contains a mix of foods, each with have a different amino acid profile.

If you have a restricted diet, consider speaking to a dietitian to check your diet contains all the nutrients for optimal health.