To the Editor We appreciate the meticulous work performed by Huang et al1 in the Original Investigation “Association Between Plant and Animal Protein Intake and Overall and Cause-Specific Mortality,” recently published in JAMA Internal Medicine. However, there are some issues to which we wish to draw attention.
First, plant proteins come as a composite food together with other nutritive parts, such as fiber and polyphenols. Emerging evidence shows that these components could be independently associated with the course and mortality of many chronic diseases, such as diabetes, cancer, and heart diseases.2,3 For example, data show a highly significant interplay between diet; consumption of fiber, including plant protein fiber; the gut microbiota; and the incidence and progression of many chronic diseases.4 In a recent study,3 consumption of dietary fiber and fiber from beans, which are also high in protein, were associated with lower all-cause mortality. Therefore, considering that plant proteins are always combined with other components, the observed association could not wholly be attributed to the amount of plant protein consumed. The other nutritive components, which have been found to greatly influence the course of cancer and other chronic diseases, may have a more significant association with outcomes.