The purpose of the study is to determine whether administration of a prebiotic, inulin, can improve the symptom complex associated with traumatic brain injury and whether inulin administration can alter the bacteria that live in the gut.

The investigators will study subjects (aged 18-70 years) with a history of moderate/severe traumatic brain injury (n=10) and healthy controls (aged 18-70 years) (n=10). All subjects will undergo a 3-month intervention of oral inulin treatment. The traumatic brain injury subjects will be administered oral inulin twice daily for 3 months. Testing including cognitive function assessment (Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), and questionnaires of fatigue, mood and quality of life and sleep will occur at month 0, 3 and 6. Blood sampling for measurement of amino acid levels, hormones, short chain fatty acids and markers of neuroinflammation will be drawn before and 90 minutes (+/- 10 minutes) after a standardized meal will occur at month 0 and month 3. In addition, fecal samples for analysis of the GI microbiome will be collected at month -1, month 0, month 1, month 2, month 3, and month 6 along with an assessment of gastrointestinal health. Traumatic brain injury subjects will be selected from residents at a long term residential rehabilitation center. Healthy control subjects will be administered oral inulin twice daily with meals for 3 months. Quality of life will be assessed by questionnaires at months 0, 3 and 6. Blood sampling for measurement of amino acid levels, hormones, short chain fatty acids and markers of neuroinflammation will be drawn before and 90 minutes (+/- 10 minutes) after a standardized meal will occur at month 0 and month 3. Fecal samples will be collected at month -1, month 0, month 3 and month 6 for analysis of the GI microbiome along with an assessment of gastrointestinal health. A member of the study team will check monthly for adverse events and overall well-being and ensure compliance and ongoing consent.