〔Abstract〕 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 re- gression 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) .