Visit 2: The subject will give the study coordinator their 3-day food diary, 14-day IBS symptom diary, and stool sample. They will provide the date of stool collection, as well as the method of storing the sample. The physician will review their 14-day IBS symptom diary and confirm their eligibility. If they continue to be eligible, the physician will do a physical exam and take their vitals (such as weight, waist circumference and blood pressure). The subject will then be asked to fill out a series of questionnaires relating to their diet (VioScreen Food Frequency Questionnaire), IBS symptoms (IBS-Quality of Life questionnaire [IBS-QoL] and IBS Questionnaire by Whorwell and Francis), sleeping/circadian patterns (2 NIH sleep questionnaires, Munich Chronotype Questionnaire, Lark/Hummingbird/Owl questionnaire, food timing questionnaire), the Expectancy and Credibility Questionnaire, and the 34-item tool asking about their GI symptoms and severity. The subject will then be randomized into one of the two groups. Depending on which group they are randomized to, they will be provided with a 6-week supply of NTX-1 OR psyllium fiber products in an identical appearing sachet along with instructions for taking the fiber. They will be provided with a 3-day food diary and a daily and weekly IBS symptom diary to fill out prior to Visit 3. This visit will be about 3 hours in length. The next visit will be 6 weeks after Visit 2.