This is a pilot trial testing enteral feeds that are high versus low in prebiotic fiber in 20 critically ill adults. The long-term goal is to determine the efficacy of fiber for the prevention of pathogen colonization/infection in the ICU.

This study will test prebiotic fiber in 20 adults who are receiving broad-spectrum antibiotics in the medical or surgical ICU by open-label randomization of patients to approximately 20 g prebiotic fiber/day including 45% short-chain fructooligosaccharides versus 0 g fiber/day by providing one of two feeds. Per 10 ounces of feed, both the high and low fiber feeds contain identical micronutrients and have 296 kilocalorie (kCal), 19 g protein, 8 g fat, and 39 g carbohydrates. The sole difference is that the fiber-containing feed has 4 g fiber including 45% short-chain fructooligosaccharides per 10 ounces whereas the other feed has 0 g fiber. Randomization will take place at the time the order for enteral feeding is placed. Rather than supplying the feed itself, the investigators will supply a randomized recommendation for a feed type (i.e., high vs low fiber) and the feed will be obtained from the hospital pharmacy in the usual manner. Determination of the feed rate and duration will be decided on the individual patient's needs by the treating ICU team. The primary outcome will be to determine whether high fiber feeds alter the gut microbiome in the face of antibiotics and critical illness, calculated by comparing within-individual microbiome differences from baseline to Day 3 in each intervention group.

Inclusion Criteria:

• Medical or surgical ICU patients ≥18 years old at our institution;
• Receiving broad-spectrum antibiotics at the time of enrollment;
• Deemed appropriate for the study by the treating ICU team;
• With capacity to give consent or have an appropriate surrogate;
• Able to undergo assessment within 4 hours of the order for enteral feeds;
• Expected to receive enteral feeds for ≥3 days but not yet receiving them.

Exclusion Criteria:

• Inability to receive enteral feeds;
• Celiac disease or known allergy to fiber;
• Surgery involving the intestinal lumen within 30 days;
• Limited treatment goals (i.e., do-not-resuscitate (DNR), do-not-intubate (DNI), or no escalation of care);
• Lack of capacity to consent and lack of an appropriate legally authorized representative.

Sequencing data and corresponding metadata will be made available through the Short Read Archive (SRA) section of the National Center for Biotechnology Information (NCBI) at the time of publication of the study results.

Data will be made available at the time of publication.

Open.