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Katz and his colleagues explain why it is obsolete.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.”
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