Objective: Randomized, double blind, placebo-controlled, crossover, clinical trial to examine the effects of the food additive glutamate (in the form of MSG) on IBS and fibromyalgia.

Setting and Subjects: The Fibromyalgia Research Database at OHSU will be utilized to identify and recruit fibromyalgia patients who also have IBS to OHSU study centers.

Intervention: Approximately 60 male and female subjects aged 18-75 will be placed on a 1-month glutamate-free elimination diet. Those that respond positively to the diet (we are estimating 30-40 subjects), will then be randomized to receive either a citrus drink containing 5 grams of MSG; or placebo (the citrus drink alone)on three consecutive days one week apart.

The investigators are hypothesizing that those who react positively to the elimination diet will have symptom occurrence statistically more frequently when given the glutamate challenge, than when given placebo.

Inclusion Criteria:

• Men and women aged 18-75 who fulfill criteria for Irritable Bowel Syndrome (IBS) and Fibromyalgia (FM)
• They must live in the greater Portland, OR, metro area, have transportation to/from study site, have access to email
• Willing to discontinue medications with bowel altering side effects

Exclusion Criteria:

• Asthma
• Inflammatory bowel disease
• Colon cancer or active endometriosis
• Any major abdominal surgery (excluding caesarean section, tubal ligation, hernia repair, gall bladder removal or appendectomy)
• Female and pregnant
• Currently taking pregabalin, gabapentin, or anti-psychotic medications and are unwilling/ unable to discontinue use
• Suffered from alcohol/substance abuse or psychosis in the last two years.