Fiber intake and risk of nonfatal acute myocardial infarction

Objective: To investigate the association between fiber intake and risk of acute myocardial infarction (AMI), also according to type and source of fiber, in a Mediterranean country. Design: Hospital-based case-control study. Setting: Northern Italy. Subjects: A total of 507 cases of first nonfatal AMI and 478 controls in hospital for acute conditions. Interventions: Subjects were interviewed with a questionnaire that included a validated food frequency section. Odds ratios (OR) were obtained using multiple logistic regression, and adjusted for several recognized risk factors for AMI. Fiber was measured as non-starch polysaccharides. Results: Compared with the lowest one, the OR in the highest tertile was 0.72 for total fiber, 0.64 for soluble fiber, 0.77 for total insoluble fiber, 0.71 for cellulose, 0.81 for insoluble non-cellulosic polysaccharides, 0.82 for vegetable fiber, 0.64 for fruit fiber and 1.11 for cereal fiber, and the estimates were statistically significant for soluble and fruit fiber. When further adjusted for β-carotene, vitamin C and vitamin E intake, the fruit fiber still showed the strongest inverse relation, although the association was no longer significant. The protective effect of fiber was more marked in, or restricted to, subjects with other AMI risk factors, such as smokers, diabetics and hypertensives. Conclusions: Though an inverse association between fiber intake and AMI risk appears established, the causality of this association is still open to debate. In this population, cereal fiber derives chiefly from refined grains, and this may explain the lack of protection by this type of fiber.