Dietary protein recommendations to support healthy muscle ageing in the 21st century and beyond: considerations and future directions

Morgan, Paul T, Witard, Oliver C, Højfeldt, Grith, Church, David D and Breen, Leigh (2023) Dietary protein recommendations to support healthy muscle ageing in the 21st century and beyond: considerations and future directions. Proceedings of the Nutrition Society. ISSN 0029-6651

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Abstract

This review explores the evolution of dietary protein intake requirements and recommendations, with a focus on skeletal muscle remodeling to support healthy ageing based on presentations at the 2023 Nutrition Society summer conference. In this review, we describe the role of dietary protein for metabolic health and ageing muscle, explain the origins of protein and amino acid requirements, and discuss current recommendations for dietary protein intake, which currently sits at ∼0.8g·kg·-1day-1. We also critique existing (e.g., nitrogen balance) and contemporary (e.g., indicator amino acid oxidation) methods to determine protein/amino acid intake requirements and suggest that existing methods may underestimate requirements, with more contemporary assessments indicating protein recommendations may need to be increased to >1.0g·kg·-1day-1. One example of evolution in dietary protein guidance is the transition from protein requirements to recommendations. Hence, we discuss the refinement of protein/amino acid requirements for skeletal muscle maintenance with advanced age beyond simply the dose (e.g., source, type, quality, timing, pattern, nutrient co-ingestion) and explore the efficacy and sustainability of alternative protein sources beyond animal-based proteins to facilitate skeletal muscle remodeling in older age. We conclude that, whilst a growing body of research has demonstrated that animal-free protein sources can effectively stimulate support muscle remodeling in a manner that is comparable to animal-based proteins, food systems need to sustainably provide a diversity of both plant and animal source foods, not least for their protein content but other vital nutrients. Finally, we propose some priority research directions for the field of protein nutrition and healthy ageing.