Lean-to-Rich Healthy Aging: A New Hypothesis on Okinawa's Postwar Nutrition Transition and Longevity Trends

This review proposes a new life-course nutritional hypothesis generated from Okinawa's unique postwar history and changing longevity advantage relative to mainland Japan. After World War II, Okinawa underwent rapid socioeconomic and dietary change and experienced a nutrition transition earlier than mainland Japan. During subsequent decades, Okinawa developed a marked relative longevity advantage, which later diminished as longevity in mainland Japan continued to improve. We propose that this pattern may partly reflect differences in the timing and sequence of life-course nutritional environments. Older Okinawan cohorts experienced an initially relatively Lean nutritional environment followed by postwar nutritional enrichment, approximating a Lean-to-Rich trajectory. Comparable trajectories may have emerged later in mainland Japan, potentially contributing to national catch-up, while progressively younger Okinawan cohorts experienced the post-transition environment from earlier life stages, increasingly approximating a Rich-to-Rich trajectory. Mortality reanalysis confirmed an older-age advantage and a progressive generational gradient. We therefore propose the Lean-to-Rich Healthy Aging Hypothesis, distinguishing three conceptual trajectories: persistent relative nutritional restraint (Lean-to-Lean), transition from an initially Lean to a subsequently Rich nutritional environment (Lean-to-Rich), and prolonged nutritional abundance (Rich-to-Rich). We hypothesize that Lean-to-Rich may be more favorable for healthy longevity than either persistent Lean-to-Lean or prolonged Rich-to-Rich. The hypothesis does not specify the optimal timing, magnitude, duration, or composition of the transition, and available ecological evidence cannot distinguish a sequence effect from cumulative Rich exposure. Rather than establishing causality, this framework generates testable predictions concerning how the sequence and duration of nutritional environments across the life course may influence healthy longevity.