Background: Prospective studies on fiber and magnesium intake and risk of type 2 diabetes mellitus were inconsistent. We examined associations between fiber and magnesium intake and risk of type 2 diabetes and summarized existing prospective studies by meta-analysis.

Methods: We conducted a prospective cohort study of 9702 men and 15 365 women aged 35 to 65 years who were observed for incident diabetes from 1994 to 2005. Dietary intake of fiber and magnesium were measured with a validated food-frequency questionnaire. We estimated the relative risk (RR) by means of Cox proportional hazards analysis. We searched PubMed through May 2006 for prospective cohort studies of fiber and magnesium intake and risk of type 2 diabetes. We identified 9 cohort studies of fiber and 8 studies of magnesium intake and calculated summary RRs by means of a random-effects model.

Results: During 176 117 person-years of follow-up, we observed 844 incident cases of type 2 diabetes in the European Prospective Investigation Into Cancer and Nutrition-Potsdam. Higher cereal fiber intake was inversely associated with diabetes risk (RR for extreme quintiles, 0.72 [95% confidence interval [CI], 0.56-0.93]), while fruit fiber (0.89 [95% CI, 0.70-1.13]) and vegetable fiber (0.93 [95% CI, 0.74-1.17]) were not significantly associated. Meta-analyses showed a reduced diabetes risk with higher cereal fiber intake (RR for extreme categories, 0.67 [95% CI, 0.62-0.72]), but no significant associations for fruit (0.96 [95% CI, 0.88-1.04]) and vegetable fiber (1.04 [95% CI, 0.94-1.15]). Magnesium intake was not related to diabetes risk in the European Prospective Investigation Into Cancer and Nutrition-Potsdam (RR for extreme quintiles, 0.99 [95% CI, 0.78-1.26]); however, meta-analysis showed a significant inverse association (RR for extreme categories, 0.77 [95% CI, 0.72-0.84]).

Conclusion: Higher cereal fiber and magnesium intakes may decrease diabetes risk.