Dietary Fiber Intake over Two Years Following Metabolic and Bariatric Surgeryis Associated with Changes in the Composition of the Gut Microbiota

Studies have shown changes in gut microbiota post metabolic and bariatric surgery (MBS) but large prospective longitudinal studies relating these changes to dietary fiber intake over time are lacking. The aim of this study was to describe the changes in the gut microbiota longitudinally over time following MBS and relate these changes to dietary fiber intake over two years following the surgery. We hypothesized that increased dietary fiber intake will support the growth of some beneficial bacteria which will in turn increase microbial metabolites required for maintaining a healthy gut and weight maintenance. Adults planning to undergo Roux-en-Y Gastric Bypass or Sleeve Gastrectomy were recruited and assessed at baseline and at 1, 6-, 12-, 18-, and 24-months post-MBS. A 24h dietary recall method (the Automated Self-Assessment 24-hour [ASA-24] Dietary Assessment Tool) was used to record dietary intake at each time point. Fecal samples were collected at each time point and analyzed using 16s rRNA sequencing. Dietary fiber from the ASA-24 recorded at baseline was 50% lower than the recommended daily intake (13.29±6.91) g/day, with the lowest recorded one-month post-MBS (4.91±3.70) g/day. Dietary fiber intake increased minimally from 6 months (7.78±4.97) g/day to 24 months (9.36 ±5.11) g/day post-MBS, remaining below the recommended daily intake. Degraders of dietary fiber such as Lactobacillus, Akkermansia, Roseburia, Bifidobacterium, Ruminococcus and Faecalibacterium increased in abundance after MBS. Although the dietary fiber intake was below the recommended intake, microbes responsible for their breakdown were abundant. In future analyses, short chain fatty acids produced from dietary fiber breakdown will be analyzed and their concentrations correlated to the amounts of dietary fiber consumed and the abundance of dietary fiber degraders. This study was funded by grants 1R01DK112585 and 3R01DK112585-01S1 from the National Institute of Diabetes and Digestive and Kidney Diseases. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.