Dietary protein considerations in a sustainable and ageing world: a narrative review with a focus on greenhouse gas emissions and skeletal muscle remodelling and maintenance.

The rise in interest of plant-based protein foods has been meteoric, often leading to calls to adopt exclusively plant-based diets to reduce the intake of animal-based foods. In addition to impacts on human health, moving to an exclusively plant-based (or indeed animal-based) diet may have detrimental implications in terms of environmental sustainability. The impact of a rapid growth in global population on the sustainability of food systems poses clear consequences for the environment and thus warrants careful consideration at a national and, in some cases, global level. The requirement for high-quality dietary protein in an ageing population to offset chronic disease, such as sarcopenia, is an additional consideration. A reductionist approach to this sustainability issue is to advise a global population switch to plant-based diets. From a dietary protein perspective, the sustainability of different non-animal-derived protein sources is a complex issue. In this review, first we describe the role of dietary protein in combatting the age-related decline in skeletal muscle mass. Next, we explore the efficacy and sustainability of protein sources beyond animal-based proteins to facilitate skeletal muscle remodelling in older age. Taking a holistic approach, we discuss protein sources in terms of the muscle anabolic potential, environmental considerations with a predominant focus on greenhouse gas emissions across the food chain, the relevance of global malnutrition, and nation- and local-specific nutritional needs for dietary protein choices and food systems. Finally, we discuss implications for environmental sustainability and explore the potential of a trade-off between diet quality and environmental sustainability with food choices and recommendations.