MODERNIZING THE DEFINITION OF PROTEIN QUALITY
Dr David Katz and colleagues call for the definition of protein quality to be modernized in their recent paper in Advances in Nutrition, because the current definition is misleading and antiquated they say. Historically, protein quality has been defined in biochemical and physiological terms reflecting the concentration of the 9 essential amino acids and their digestibility from specific food sources. The resulting measure, the Protein Digestibility Corrected Amino Acid Score (PDCAAS), is what the Food and Drug Administration (FDA) in the United States uses to measure protein quality in foods.
Katz and his colleagues explain why it is obsolete. “The popular concept that protein is “good,” and that the more the better, coupled with a protein quality definition that favors meat, fosters the impression that eating more meat, as well as eggs and dairy, is desirable and preferable. This message, however, is directly opposed to current Dietary Guidelines for Americans, which encourage consumption of more plant foods and less meat, and at odds with the literature on the environmental impacts of foods, from carbon emissions to water utilization, which decisively favor plant protein sources. Thus, the message conveyed by the current definitions of protein quality is at odds with imperatives of public and planetary health alike.”
In their paper, Katz and colleagues propose a modernized definition, which incorporates the quality of health and environmental outcomes associated with specific food sources of protein.
They also demonstrate how such an approach can be adapted into a metric, and applied to the food supply. Their metric still considers the distribution of essential amino acids, and their digestibility – but also considers, and weights appropriately, the net effects of the food on our overall health, and its environmental footprint. By such a measure, beans and lentils shoot up to the top of the rankings, and beef, for example, falls down because while it is indeed a concentrated protein source, it’s a food we should be eating less, not more. They conclude: “The adoption of such a shift in protein quality assessment would allow for clearer, more consistent messaging to the public and better alignment of nutrition policy with nutrition science.”