From Global Plates to Physiological States: A Multi-Scale Analysis of Dietary Protein Source in Human Ageing

Abstract

This thesis examines how plant-based (PB) versus animal-based (AB) protein affects human health across the lifespan, focusing on age-specific mortality and integrated biomarker indices, and how these effects manifest across biological scales amid global food system transitions. Global food systems produce roughly one-third of anthropogenic greenhouse gas emissions, creating pressure to adopt sustainable protein sources. The health effects of replacing AB protein with PB protein remain unclear across life stages. Although PB diets are linked to lower chronic disease risk and greater longevity, protein requirements and metabolic responses vary with age. Prior research has largely relied on single-scale analyses that overlook macronutrient interactions. This thesis applies the Geometric Framework for Nutrition to examine non-linear, interactive effects. Chapter 2 presents a population-level analysis examining associations between national protein supply and age-specific mortality. Chapter 3 presents an individual-level analysis examining associations between dietary protein intake and biomarker-based measures of physiological health. Chapter 4 presents a controlled intervention examining the effects of omnivorous versus vegetarian whole-food diets on biological age in older adults. At the population-level AB protein was associated with improved early-life survival but compromised late-life survivorship in high-fat nutritional environments. Individual-level analyses revealed systemspecific responses shaped by carbohydrate and fat intake. Intervention analyses confirmed these patterns, with older adults on PB diets showing improvements in biological age while omnivorous high-fat diets showed no benefit. These findings indicate that protein effects vary with age and macronutrient context, highlighting the need for age-specific guidance, targeted interventions, and multi-scale approaches to inform nutrition policy integrating human health and environmental sustainability.