A gram of prevention: a modest increase in fiber consumption may reduce risk of preeclampsia.

E vidence from randomized, controlled clinical trials shows that a diet high in total fiber (i.e., >25 grams/ day (g/d)) is associated with decreases in blood pressure, insulin resistance, and markers of cardiovascular disease, including cholesterol, triglycerides, and inflammation.1,2 In this issue, Qiu et al.3 report a significant protective effect of fiber intake during the first trimester of pregnancy on subsequent risk of preeclampsia. This paper is timely. Few epidemiological studies have investigated dietary fiber intake and risk of preeclampsia. Moreover, clinical trials testing for protective effects of aspirin, calcium, and vitamins C and E on preeclampsia risk have reported null findings, and new reports indicate increased population rates of preeclampsia,4 leaving clinicians with little evidence-based preventative advice to offer. This study has several strengths. First, data come from the Omega Study, an ongoing cohort study of maternal dietary and lifestyle risk factors for preeclampsia. Second, the authors asked women at ~13 weeks gestation about their firsttrimester diet using the psychometrically sound Women’s Health Initiative Food Frequency Questionnaire (WHI FFQ). WHI FFQ reliability studies report minimal 3-month recall bias and high validity across ethnic groups.5 Furthermore, the authors obtained blood samples at about 14 weeks gestation to examine the association between total fiber intake and plasma lipid concentrations. As projected, increased fiber intake was associated with decreased levels of triglycerides and increased levels of HDL-cholesterol. Not known is whether total fiber intake or its lipid level correlates conferred greater protection against preeclampsia, because the authors did not include triglyceride and HDL-cholesterol levels in the same model. This study reports a stronger association between dietary fiber intake and preeclampsia than previously reported.6,7 Qiu et al. found a 67% reduction preeclampsia risk (relative risk (RR): 0.33, confidence interval (CI): 0.14–0.79) when comparing the highest to lowest quartiles of total fiber intake. Using current definitions of preeclampsia, the comparable level of protection was only slightly less at 63% (RR: 0.37, CI: 0.12–1.12). The authors conclude that a diet high in fiber (i.e., ≥21.2 g/d) is associated with a significant reduction in risk of preeclampsia. Of note, significant reductions in risk were also observed in the second and third quartiles of intake, suggesting that even moderate fiber intake confers protection compared to very low intake (<11.9 g/d). If adequately powered, this or future studies should analyze fiber intake as a continuous variable to identify clinically relevant thresholds. Generalizeability is limited given the number of cases (n = 64). Frederick et al., using a different sample of subjects from the Omega Study with more cases (n = 172), also reported reduced preeclampsia risk with increased fiber intake over the course of pregnancy. Their data collection, timing of exposure, and intake quartiles, however, differed in ways that could limit comparability. The suggestion that a moderate consumption of dietary fiber may reduce risk of preeclampsia has public health importance. The difference between first and second quartile medians is about 5 g—roughly three tablespoons of bran cereal or a large, raw apple. Encouraging women with low-fiber intake to eat a small serving of cereal or an apple gives pregnant women a far less daunting goal than asking them to consume the 28 g/d of fiber currently recommended.8 Moreover, when compared to medical interventions, modest dietary change is low cost, easy to implement, and low risk. New well-powered cohort studies and clinical trials that assess fiber intake prior to and during the entire course of gestation should be conducted. Such research can expand etiologic insights into the role of obesity, insulin resistance, and dyslipidemia in the common end point of preeclampsia.