Examining widely held propositions on human dietary protein needs and benefits: a critical review of the science that shapes both the data and our understanding of an essential macronutrient

The essentiality of protein in the human diet is unequivocal. Yet researchers, clinicians, and lay people often believe numerous propositions about dietary protein despite insufficient supporting or refuting data in some instances. To address this disconnect, and to "pressure-test" current beliefs about dietary protein, the Indiana University School of Public Health-Bloomington convened a workshop in February 2025 titled "Human Dietary Protein Needs and Benefits: A Critical Assessment of Postulated Propositions." More than 20 international experts discussed (1) methodologic issues affecting data acquisition and interpretation; (2) "optimal" dietary protein intakes and effects on muscle protein synthesis rates, muscle protein accretion, muscle growth, and muscle repair; (3) protein needs during weight loss; (4) acute protein intake thresholds above and below which protein is no longer related to anabolism; and (5) dietary protein intakes above which protein may be detrimental to health. The experts rated each proposition on a scale from "existing evidence strongly supports the proposition" to "existing evidence seems sufficient to rule out the viability of the proposition." In most instances, the experts believed additional research was warranted. For many propositions the research base was insufficient in terms of quality (rigor), quantity (sample size, study duration), or pertinence (e.g., use of surrogate markers).