Association Among Eating Speed, Dietary Diversity, and Fat-Free Mass Index in Adults.

OBJECTIVE: Dietary diversity and eating behaviour are recognised as factors influencing body composition; however, their association with fat-free mass index and body fat mass index remains unclear. METHODS: This cross-sectional study analysed the relationships among body composition indices (BMI, FFMI, BFMI), self-reported eating speed, and dietary diversity in 10 644 healthy adults aged 18-64 years (4419 women and 6225 men; mean age 41.9 years) who visited hospitals for health checkups. RESULTS: The dietary variety score showed a positive association with muscle mass in men and a significant negative association with body fat mass index in women (fat-free mass index: β = 0.03, 95% confidence interval: 0.01 to 0.05, p = 0.04; body fat mass index: β = -0.07, 95% confidence interval: -0.15 to -0.01, p < 0.01). Regarding eating speed, a consistent trend was observed in both sexes: the fast-eating group showed significantly higher body mass index, fat-free mass index, and body fat mass index values (p < 0.01), whereas the slow-eating group had lower values. CONCLUSIONS: These associations were more pronounced in men than in women. Both dietary diversity and eating speed were associated with body composition indices, with notable sex-related differences. These findings suggest that dietary behaviour and diversity may influence body composition.