Describe the impact of fiber on the upper and lower GI tract.

• A. Upper GI transit is faster, and fiber in the lower GI slows transit.
• B. Fiber has no effect on upper GI and speeds lower GI.
• C. Upper GI transit is slower (especially with soluble fibers); lower GI transit hastens due to increased stool weight, water, and bacterial mass.
• D. Upper GI transit speeds up with soluble fiber, lower GI slows due to fiber fermentation.

Answer: (C)