Redefining Protein Quality:  What’s New About Protein?

by Vesanto Melina, MS, Registered Dietitian

A paper published by the American Society for Nutrition makes the case for modernizing the definition of protein quality. This is a welcome development. The current definition is outdated and fails to protect public health because it assesses how well various proteins meet human requirements based solely on digestibility and the content of essential amino acids. People may think this narrow definition is a good thing, but protein-rich animal products such as cured meats (ham, bacon, sausage, hot dogs, and so on) can get high protein quality ratings even though the World Health Organization has placed them in the same “convincing carcinogens” category as roundup/glyphosate, asbestos, and cigarette smoke. Red meats (such as beef and lamb) can also get high ratings for protein quality under the current definition, but these are  classified by the WHO as a “probable carcinogen”.

Moreover, the production of these foods has huge and devastating environmental impacts. (For outstanding research see  Poore & Nemecek (2018) Reducing food’s environmental impacts through producers and consumers. Science.    [free pdf

In response, dietary choices are changing, feedlots are closing, meat subsidies are being questioned, and a British University is banning beef from its menus.

To give some historical background, early research on protein, which began over a half-century ago, mainly used rats to provide biological data. As it turns out, these small mammals have significantly different protein needs from those of humans. Baby rats double their birth weight in 4 days and triple it in a few weeks. Humans are not meant to gain weight that fast – and do not want to! Rats also have fur, and growing fur uses specific amino acids. The research rats were only allowed a single food as their protein source, such as meat, egg, or wheat, rather than the mix that any animal or human would freely choose. The animals were slaughtered when experiments ended, ensuring that any long-term health impacts on the rats never came to light.

The limited parameters of this early research led us to undervalue plants as a quality source for our somewhat different human protein needs. Early research also found protein deficiency in some malnourished populations whose diets were mainly plant-based. It was later recognized that the real nutrition problem stemmed from lack of food variety (such as 80 percent of calories from unleavened bread, or from rice), and insufficient calorie intake. More recent research has clearly established that human protein and essential amino acid requirements are easily met by entirely plant-based diets.

A modernize definition of protein quality should therefore include:

  • the concentration of protein and amino acids required to meet our human needs
  • evidence of health outcomes
  • potential environmental impacts.

Plant foods pack more nutrients into fewer calories. They promote a healthy gut microbiome, and are strongly associated with lower risk of chronic disease. And their environmental impacts and carbon footprint are far smaller.

Vesanto Melina is a Vancouver Dietitian and author of award-winning nutrition books.


Katz DL et al. Perspective: The Public Health Case for Modernizing the Definition of Protein Quality. Adv Nutr. 2019 May 8. pii: nmz023.

Davis B, Melina V. Becoming Vegan: Comprehensive Edition Book Publishing Co.

O\’Malley K et al. Vegan vs Paleo: Carbon Footprints and Diet Quality of 5 Popular Eating Patterns as Reported by US Consumers (P03-007-19). Curr Dev Nutr. 2019 Jun 13;3(Suppl 1).

Poore & Nemecek (2018) Reducing food’s environmental impacts through producers and consumers. Science.  [free pdf]   Also see the lecture at   and see

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