Objective: To assess the association between Life eight ( LE8) scores and diabetes mellitus ( DM) ， and to examine the mediating effect of Methylmalonic acid (MMA). Methods: Based on cross-sectional data from the 2011—2014 National Health and Nutrition Examination Survey (NHANES) ，weighted multivariable logistic regression analyses were conducted to assess the association between the LE8 score and DM．A mediation model was further constructed to evaluate the mediating effect of MMA． Results: The weighted multivariable logistic regression analysis showed a significant negative correlation between LE8 score and the risk of DM．After adjusting for poten- tial confounders，a 1-point increase in LE8 was associated with a 7% reduction in DM risk ( OR = 0. 93，95% CI: 0. 92－0. 93，P = 0. 000 1) ．In contrast，the level of circulating MMA did not show a statistically significant rela- tionship with DM risk ( OR = 0. 99，95% CI: 0. 89 －1. 10，P = 0. 886 8) ．Further subgroup analysis by age re- vealed that in participants under 60 years of age，circulating MMA levels were positively associated with DM risk ( OR = 1. 39，95% CI: 1. 19 －1. 62 ，P ＜0. 000 1 ) ． Mediation analysis indicated that circulating MMA levels played a partial mediating role in the relationship between LE8 and DM，with a mediation ratio of 1. 5% (P < 0. 000 1) ． Conclusion High LE8 scores significantly reduce the risk of DM ，and circulating MMA levels may play a role in this，particularly among individuals younger than 60 years (individuals＜60 years of age