Chinese Healthy Eating Index and incident obesity: a prospective cohort study with repeated dietary assessments

Background Obesity is a growing public health challenge in China. Evidence remains limited on the association between incident obesity and long-term dietary quality repeatedly measured with the Chinese Healthy Eating Index (CHEI). Methods We analyzed longitudinal China Health and Nutrition Survey (CHNS) data collected in Hubei Province. The study included 1,527 adults aged ≥20 years without obesity at baseline who participated in at least two survey waves between 1991 and 2023. At each wave, diet was based on three consecutive 24-h recalls and parallel household food weighing over the same three days. We summarized long-term diet quality using the cumulative mean of available CHEI scores through the event or final follow-up. Cox models provided hazard ratios (HRs) and 95% confidence intervals (CIs) for incident obesity, and restricted cubic splines (RCS) characterized the shape of the association. Results Across 23,193 person-years of observation (median follow-up, 14.0 years), 159 incident obesity cases occurred. A 5-point increase in cumulative average CHEI score corresponded to an adjusted HR of 0.81 (95% CI: 0.68–0.96), representing a 19% lower hazard of incident obesity. The spline curve was L-shaped ( P for nonlinearity = 0.029): obesity hazard declined more sharply across the lower CHEI range and changed little at higher scores. In component analyses, per SD increases in the scores for whole grains and mixed beans (HR = 0.69; 95% CI: 0.56–0.85) and dark vegetables (HR = 0.78; 95% CI: 0.65–0.94) were associated with lower hazards of incident obesity. When the components were mutually adjusted, only the whole grains and mixed beans association remained robust (HR = 0.73; 95% CI: 0.59–0.91). Conclusion Adults with higher long-term CHEI scores had a lower incidence of obesity in Hubei Province, China, with an L-shaped dose–response pattern, suggesting that the potential for improvement is greatest among adults with poorer-quality diets. The findings indicate that improving and maintaining overall diet quality over time may be relevant to obesity prevention.