SIBO Center for Digestive Health at NCNM

Meet Our Providers

Steven Sandberg-Lewis, ND, DHANPssl_2013_188

Dr. Steven Sandberg-Lewis has been a practicing naturopathic physician for 36 years, previously on Orcas Island in Washington state and now exclusively at the NCNM Clinic.  Dr. Sandberg-Lewis receives referrals of patients with digestive diseases who desire naturopathic treatment options; often these are conditions that have defied diagnosis by other physicians. He understands the diseases of the gastrointestinal tract, but also can assess function and often find successful treatments to regain normal function of the digestive system.

Allison Siebecker, ND, MSOM, LAc

Allison Siebecker, ND, MSOM, LAc, is the co-founder and Medical Director of the SIBO Center for Digestive Health at NCNM Clinic in Portland, OR, where she specializes in the treatment of SIBO. She is instructor of advanced gastroenterology at NCNM, teaches continuing education classes on SIBO, nutrition and gastroenterology for physicians, and is the author of the educational website  She is a frequent guest on health podcasts, summits and internet radio and is writing a book synthesizing the SIBO data into one source.

Dr. Siebecker received her Doctorate in Naturopathic Medicine and her Masters in Oriental Medicine from NCNM in 2005. She is an award winning author, having received the Best in Naturopathy award from the Townsend Letter in 2005, 2013 and 2015, for her articles “Traditional Bone Broth in Modern Health and Disease”(2005),  “Small Intestine Bacterial Overgrowth: Often Overlooked Cause of IBS” (2013) and SIBO: Dysbiosis Has A New Name (2015) (co-authored with Steven Sandberg-Lewis, ND, DHANP).

Melanie Keller, ND

Dr. Melanie Keller is an NCNM alumna and SIBO Center physician specializing in the treatment of digestive disorders. She currently serves as president of Gastro ANP. Her evidence-based naturopathic approach focuses on addressing the whole person by utilizing functional testing, nutrition, energetic psychology techniques, and visceral and structural manipulation.

While a student at NCNM, Dr. Keller had the privilege of an extensive internship with the renowned Dr. Steven Sandberg-Lewis. His influence during and after this internship greatly enhanced Dr. Keller’s practice philosophy. She has also received post-graduate extended training in Small Intestine Bacterial Overgrowth (SIBO) with Dr. Allison Siebecker. Dr. Keller has applied this training in her functional medicine practice where she has helped many patients to restore their health and vitality.

The SIBO-IBS Center wishes to thank Dr. Siebecker for her contribution of information about SIBO on this site. For more information about SIBO, visit her educational website at