Objective: To better understand the association between a modified Mediterranean diet pattern in young adulthood, cardiorespiratory fitness in young adulthood, and the odds of developing pre-diabetes or diabetes by middle age. Research design and methods: Participants from the Coronary Artery Risk Development in Young Adults (CARDIA) study who did not have pre-diabetes or diabetes at baseline (year 0 (Y0), ages 18-30) and who had data available at the Y0 and year 25 (Y25) visits were included in this analysis (n=3358). Polytomous logistic regression models were used to assess the association between baseline dietary intake and fitness data and odds of pre-diabetes or diabetes by middle age (Y25, ages 43-55). Results: At the Y25 visit, 1319 participants (39%) had pre-diabetes and 393 (12%) had diabetes. Higher baseline fitness was associated with lower odds of prediabetes and of diabetes at Y25. After adjustment for covariates, each SD increment in treadmill duration (181 s) was associated with lower odds for prediabetes (OR 0.85, 95% CI 0.75 to 0.95, p=0.005) and for diabetes (OR 0.71, 95% CI 0.60 to 0.85, p=0.0002) when compared to normal glycemia. A modified Mediterranean diet pattern was not associated with either pre-diabetes or diabetes. No interaction between cardiorespiratory fitness and dietary intake was observed, but baseline fitness remained independently associated with incident pre-diabetes and diabetes following adjustment for diet. Conclusions: Higher cardiorespiratory fitness in young adulthood, but not a modified Mediterranean diet pattern, is associated with lower odds of prediabetes and of diabetes in middle age. Trial registration number: NCT00005130.