Longitudinal Associations of Dietary Fiber Intake with Glycated Hemoglobin and Estimated Insulin Sensitivity in Adults with and without Type 1 Diabetes

Dietary fiber, an essential bioactive compound in plant-based diets, is of public health concern based on habitual low intakes in the general population. Not much data are available on how habitual dietary fiber is associated with glycemic control in type 1 diabetes (T1D) as well as in prediabetes and normoglycemic adults. To address this gap, we conducted a six-year longitudinal analysis of an original cohort in adults with and without T1D (n = 1255; T1D: n = 563; non-diabetes mellitus (non-DM): n = 692). Dietary data were collected from a validated food frequency questionnaire, biochemical measures were obtained after an overnight fast, and anthropometric measurements were collected at baseline as well as after three and six years for the follow-up study. Glycated hemoglobin (HbA1c) and estimated insulin sensitivity (eIS) were the main outcomes examined. In adjusted analyses, dietary fiber intake was inversely associated with HbA1c in a minimally adjusted model, but it was positively associated with eIS in a model involving all relevant covariates in non-DM adults. These associations were not significant in the T1D group. Furthermore, when examined by HbA1c cut-offs for glycemic control, an inverse association with dietary fiber was only observed in adults with prediabetes (all p < 0.05). At a six-year mean (±SD) dietary fiber intake of 17.4 ± 8.8 g for non-DM and 17.0 ± 8.2 g for the T1D group, protective associations against poor glycemic control were observed in those without diabetes and in prediabetes.