Caloric Intake at Lunch Does Not Mediate the Impact of Eating Rate on Weight Gain Among Healthy Adults: Longitudinal Cohort Study

PurposeThis study aims to evaluate causal relationships among eating rate, caloric intake, and weight gain using longitudinal data and to clarify how caloric intake mediates the effect of eating rate on weight gain.DesignA longitudinal cohort study with a 4-year follow-up.SettingData were collected from Daihatsu Co, Ltd employees, a major Japanese automobile manufacturer with 4 plants in Japan.SubjectsOf the 12,816 working-age Japanese individuals who underwent health checkups in 2020, 7,784 without excess weight or non-communicable diseases were included.InterventionThe eating rate was self-reported, and caloric intake was calculated based on cafeteria meal choices.MeasuresAnnual change in body mass index (BMI), calculated as the difference in BMI between consecutive years.AnalysisMediation analyses using a mixed-effects model were conducted to assess whether caloric intake mediates the effect of eating rate on BMI.ResultsCaloric intake in the fast-eating and ordinal-eating groups exceeded that of the slow-eating group by 19.21 kcal [9.28, 29.13] and 10.01 kcal [1.20, 18.81], respectively. Higher caloric intake was associated with a more significant BMI increase, rising by .09 [.06, .13] per interquartile range increase. The proportion of mediated impact among the impact of eating rate is .19% [.09, .32].ConclusionFaster eating independently contributes to BMI increases, with minimal mediation by caloric intake. Interventions targeting eating pace may prevent obesity, though the study population may limit generalizability.