Interventions to prevent excessive gestational weight gain (GWG) have found limited success likely due to a lack of targeting mechanisms that drive GWG. Dietary fiber is a powerful prebiotic that changes the gut microbial composition and is related to reduced weight gain. No studies have assessed the impact of a high fiber (HF) diet on GWG. The purpose of this study was to assess the impact of a HF diet on GWG, fat accrual, and gut microbial changes during pregnancy.


Pregnant women were block randomized into a HF (>30 g/day; n=12) or usual care (UC; n=8) group. The 12-week intervention included weekly lessons to increase fiber intake. High-fiber snacks (10-12g/day) were provided for the first 6 weeks. Body weight, body composition (measured using the three-component model), and stool were measured or collected at baseline and 12 weeks. The microbial composition was profiled by sequencing the 16S rRNA gene V3-V4 region on the MiSeq Platform. Kruskal-Wallis examined changes in relative abundance between groups.


The HF group gained less weight (7.0 vs. 4.0 kg; p=0.044) and accrued less fat (5.1 vs. 2.5 kg; p=0.04) during the 12-week intervention. Looking at relative abundance of 9 phyla, Firmicutes and Bacteroidetes had the most evident change with decreased Firmicutes and increased Bacteroidetes in the HF group. The change in Firmicutes-Bacteroidetes ratio was significant when compared to the UC group (-2.3 vs. 3.75; p=0.03).


The HF group had less GWG, fat accrual, and decreased their Firmicutes-Bacteroidetes ratio, which is a favorable shift in microbial composition.