Popular Protein Quality Scoring System (“DIAAS”) Should be Avoided for Plant-Based Diets and Exercise

A popular protein quality scoring system commonly used to prop up animal products should not be applied to plant-based diets, according to a new scientific paper. The scholarly review, published in Current Nutrition Reports and co-authored by the GCI team, explains why this approach is poorly suited not only to those who eat plant-based diets, but to athletes as well.

The Digestible Indispensable Amino Acid Score (DIAAS) was developed to help avoid global malnutrition, and can be useful in economically undeveloped nations. Its relevance to people following plant-based diets in developed nations however, is highly suspect. Typical Western plant-based diets surpass protein recommendations by 24% and common plant-based foods easily exceed indispensable amino acid (IAA) requirements. Recommendations to consume “high-quality” proteins, a poorly defined term frequently used to characterize animal foods, would lead people to overshoot IAA requirements by 40%. The authors, led by Joel Craddock of The University of Sydney, concluded, “Such inconsistencies cast doubt upon the utility of the DIAAS in informing the selection of protein sources for Western adult populations, including those who adhere to entirely plant-based diets.”

The team illuminated the tendency of the DIAAS to disproportionately penalize plant proteins and diets built around them in a number of ways. For example, all proteins contain nitrogen, but different sources contain different amounts. Recommendations were made to overlook this discrepancy when calculating the DIAAS by using a single, generalized factor for all foods. It turns out that using this oversimplified and inaccurate factor lowers the apparent scores for almonds and soybeans by 17% and 10%, while inflating scores for animal foods like skim milk and yogurt.

As another example, research on DIAAS-based protein digestibility in athletes has omitted contributions made by fruits and vegetables. People eating plant-based diets however, typically eat much more produce than those eating omnivorous diets, so dismissing these food groups disproportionately diminishes their scores. Beans and grains are also docked points since  raw foods are usually used to calculate DIAAS, and the digestibility of these foods increases significantly when they’ve been cooked, which they almost always are. 

The authors detailed several other limitations of the DIAAS, and noted its reappropriation from a tool designed to mitigate malnutrition in a global setting to a ranking system for the muscle-building potential of proteins in an exercise setting. They emphasized that the DIAAS wasn’t built for this purpose and quoted other scientists who acknowledged that it fails to consider “downstream physiological targets of interest to a physically active person or athlete.” As such, its use in the context of exercise is misguided and inappropriate.

The researchers concluded with a reminder that fixating on protein quality misses the forest for the trees. “As our understanding of plant-based nutrition has improved,” they wrote, “it has become increasingly apparent that emphasizing protein quality in developed nations is unproductive, influencing food selection with irrelevant metrics rather than more important dietary factors and truly prevalent nutritional shortcomings (i.e., fiber). Pervasive use of DIAAS and food selection based on this score is thus futile at best and harmful at worst.”

For more information, please contact info@gamechangersinstitute.com or access the full paper at https://rdcu.be/cdaPX.

Reference:

Craddock JC, Genoni A, Strutt EF, Goldman DM. Limitations with the Digestible Indispensable Amino Acid Score (DIAAS) with Special Attention to Plant-Based Diets: a Review [published online ahead of print, 2021 Jan 6]. Curr Nutr Rep. 2021;10.1007/s13668-020-00348-8. doi:10.1007/s13668-020-00348-8