Mark Pimentel, M.D., FRCPC, is Associate Professor of Medicine in Gastroenterology at Cedars-Sinai Medical Center, where he also serves as Executive Director of the Medically Associated Science and Technology (MAST) Program. He holds a faculty appointment at the Geffen School of Medicine at UCLA. Dr. Pimentel earned both his bachelor’s degree in microbiology and biochemistry and his medical degree from the University of Manitoba in Winnipeg, where he also completed his internal medicine residency. He continued his training with a fellowship in gastroenterology through the UCLA-affiliated program.

Dr. Pimentel is internationally recognized for pioneering research that reframed irritable bowel syndrome (IBS) as an organic, microbiome-driven disease. He and his team established the connection between small intestinal bacterial overgrowth (SIBO) and IBS, identifying IBS as an autoimmune condition triggered by infection. His work led to the development of the first blood tests for IBS, known as IBS-Smart, and to the discovery of rifaximin as an effective therapy for IBS with diarrhea. He also developed breath testing methods to measure hydrogen, methane, and hydrogen sulfide, providing more precise diagnostics to differentiate SIBO, intestinal methanogen overgrowth, and related conditions.

As head of the MAST Program, Dr. Pimentel leads a multidisciplinary team advancing microbiome-based diagnostics, therapeutics, and devices for disorders of gut motility, IBS, SIBO, and metabolic dysfunction. He has authored extensively in leading journals, including the New England Journal of Medicine, Annals of Internal Medicine, and the American Journal of Gastroenterology. Board-certified in internal medicine and gastroenterology, he is a fellow of the Royal College of Physicians and Surgeons of Canada and an active member of numerous professional societies in gastroenterology and motility research.