A colonoscopy exam is only as good as the doctor who performs it. The ability to spot a cancerous polyp in the colon during a colonoscopy, no matter now small in the size, is what separates an exceptional doctor from an average one. At the La Peer Colonoscopy Center of Excellence, our doctors are second to none.

Our physicians were trained at the top medical schools in the country. They are involved in cutting-edge research, have written textbooks, are published in peer-reviewed publications, and have lectured to physicians around the world. Our doctors have also been featured in national media such as Discovery Health, The Oprah Winfrey Show, The Doctors, The New York Times, People, Entertainment Tonight, The Insider, CNN, ABC News, Fox 11 News, and ELLE magazine and more.

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Medical Directors at the Colonoscopy Center of Excellence


Shabab Mehdizadeh, MD, GastroenterologyShahab Mehdizadeh, MD

A co-director of the Colonoscopy Center of Excellence, Shahab Mehdizadeh, MD is board-certified in gastroenterology, internal medicine, and diseases of the liver. His research focuses on new and advanced endoscopic techniques with particular emphasis on prevention of cancers of the colon. Dr. Mehdizadeh greatly values the importance of nutrition in the treatment and prevention of disorders. He is board certified by the American Board of Physician Nutrition Specialists.

Dr. Mehdizadeh has been involved in numerous research projects and is published in several major journals (see publications). His research focuses on new and advanced endoscopic techniques. He has received a letter of recognition from the Journal of Gastrointestinal Endoscopy for his outstanding publication. He also received the Senior Fellow Abstract Award and the Best Clinical Research Award by the American College of Gastroenterology.

In obtaining his Bachelors and Masters degrees from the University of California Los Angeles (UCLA) with both departmental honors and UCLA college of letters and sciences honors, Dr. Mehdizadeh was also awarded the prestigious UCLA Chancellor Service award for his contributions to the University. He then attended the University of Rochester School of Medicine where he received commendations on his performance on two consecutive years. He subsequently completed his residency in internal medicine at Cedars-Sinai Medical Center where he was the recipient of the American Liver Foundation and the AASLD Resident Scholar Award. Dr. Mehdizadeh then completed three years of specialty training in gastroenterology and liver disorders at the combined UCLA/Cedars-Sinai Medical Center program. You can learn more about Dr. Mehdizadeh at www.beverlyhillsdigestivecare.com.

Arash Ari Nowain, MD, GastroenterologyArash Ari Nowain, MD

Arash Ari Nowain, MD, co-director of the Colonoscopy Center of Excellence, is board-certified in gastroenterology and internal medicine and specializes in medical disorders of the digestive system. Dr. Nowain treats acute and chronic GI problems with a heavy focus on prevention of colon cancer. Dr. Nowain has staff privileges at the Cedars-Sinai Medical Center and other local hospitals in Los Angeles. He is a Los Angeles native and is thrilled to practice where he grew up.
Dr. Nowain received his medical degree from the University of Southern California, Keck School of Medicine and was the recipient of the Clinical Medicine Scholarship award in his fourth year of medical training. He completed three years of residency training in Internal Medicine at the Los Angeles County / USC General Hospital. In all three years of residency, Dr. Nowain received the Resident of the Year award. He then completed three years of fellowship training in the Department of Gastroenterology and Liver Diseases at the USC Keck School of Medicine.

In addition to being one of the directors of the Colonoscopy Center of Excellence, Dr. Nowain also is the founder of the Center for GI Health. In his private practice, Dr. Nowain specializes in medical disorders of the digestive system which includes the esophagus, stomach, small intestine, colon, liver, gallbladder, pancreas, and hemorrhoids. He performs an array of diagnostic and therapeutic techniques including upper endoscopy (EGD) and lower endoscopy (colonoscopy). He treats acute and chronic GI problems and also focuses heavily on prevention of diseases such as colon and esophageal cancer.

The Rest of Our Talented Team

Siamek Tabib, MD, GastroenterologySiamak Tabib, MD

Siamak Tabib, MD is board-certified in Internal Medicine, Gastroenterolgy and Hepatology. Dr. Tabib incorporates both health maintenance and disease prevention in his practice of Gastroenterology and Hepatology. These two specialty fields of medicine deal primarily with conditions of the digestive tract. His goal is to maintain health primarily through disease prevention, and when necessary, to intervene with appropriate state of the art methods.

Payman Khorrami, MD, GastroenterologyPayman Khorrami, MD

Payman Khorrami, MD is board-certified in Gastroenterology and Hepatology and has had the additional education to diagnose and treat complex gastrointestinal problems. He has been expertly trained to perform colonoscopies when they are required to determine the cause of a patient’s complaints. Dr. Khorrami has appeared on several television and radio talk shows to discuss disorders of the gastrointestinal tract.

Mark Davidson, MD, GastroenterologyMark Davidson, MD

Mark Davidson, MD is board-certified in both Gastroenterology and Internal Medicine. Dr. Davidson is an Attending Physician at Cedars Sinai Medical Center and other local hospitals in Los Angeles. He graduated from David Geffen School of Medicine at University of California, Los Angeles (UCLA) and completed his residency in internal medicine at UCLA-Veterans Affairs Medical Center. His practice focuses on clinical medicine and a variety of endoscopic procedures. Thousands of patients seeking a qualified Los Angeles gastroenterologist have trusted their medical care to Dr. Davidson for a variety of medical disorders but especially for screening of colon cancer. In addition, he specializes in treating cases such as constipation, fecal incontinence, hepatitis, hemorrhoids, and more.

Leo Treyzon, MD, MS, GastroenterologyLeo Treyzon, MD, MS

Leo Treyzon, MD, MS is board-certified in gastroenterology and clinical nutrition with a sub-specialization in nutrition and obesity. He is currently the Chief of Gastroenterology at Cedars-Sinai Medical Center. He also serves on the Cancer Committee at Cedars Sinai and is an active member in four Centers of Excellence at Cedars Sinai: Weight Loss Center, Esophageal Disorders Center, the Colorectal Cancer Center, and the Inflammatory Bowel Disease Center.

Peyton Berookim, MD, Gastroenterology

Peyton Berookim, MD

Peyton Berookim, MD is board-certified by the American Board of Internal Medicine and Subspecialty Board of Gastroenterolgy. Dr. Berookim’s key areas of interest are colon cancer screening, surveillance, and prevention. As a member of the American College of Gastroenterology and the American College of Physicians, Dr. Berookim has placed special emphasis on continually educating himself on the latest and most advanced procedures and treatments in gastroenterology.

Maurice Elihu, MD, Gastroenterology

Maurice Elihu, MD

Dr. Maurice Elihu is a board-certified gastroenterologist that specializes in the comprehensive evaluation and prevention of colorectal cancers. He believes that the key to proper diagnosis and treatment is personal attention to every patient. Dr. Elihu is an active member of American College of Gastroenterology & Southern California Society of Gastroenterology as well as a Diplomate of the American Board of Internal Medicine and American Board of Gastroenterology.

Farshid Sam Rahbar, MD, GastroenterologyFarshid Sam Rahbar, MD

Farshid Sam Rahbar, MD is the leading integrative gastroenterologist in Los Angeles, California. He is board-certified in Gastroenterology, Internal Medicine, Integrative Holistic Medicine, and Anti-Aging, Regenerative, and Functional Medicine. Dr. Rahbar incorporates anti-aging & functional medicine for an integrative-holistic approach to digestive care. He brings over 20 years of excellent technical skills in endoscopy and colonoscopy along with a Holistic-Integrative approach to each.

Eiman Firoozman, MD, ColorectalEiman Firoozmand, MD

Eiman Firoozmand, M.D. is board certified in colorectal and general surgery. He is currently Chief of the Division of Colorectal Surgery at Cedars-Sinai Medical Center in Beverly Hills. Dr. Firoozmand’s main practice involves treatment of colon and rectal cancer. Dr. Firoozmand has written numerous articles for peer-reviewed publications including The American Surgeon, The Journal of Trauma, and Surgical Laparoscopy & Endoscopy.

Liza M. Capiendo, MD, ColorectalLiza M. Capiendo, MD

Liza M. Capiendo, MD is board-certified by and a member of The American Society of Colon and Rectal Surgeons. Dr. Capiendo has published the results of her original research on the Radiotherapeutic Pretreatment of Colon Xenografts in The Journal of Immunopharmacology and has also presented the results of her investigation into recurrent colon and rectal cancer to The American Society of Colon and Rectal Surgeons Convention in Philadelphia. Dr. Capiendo is currently serving as the Clinical Chief of the Department of Colon and Rectal Surgery at Cedars Sinai Medical Center in Los Angeles.

Gary Hoffman, MD, ColorectalGary Hoffman, MD

Gary Hoffman, MD is a board-certified colorectal surgeon. He is a member of The American Society of Colon and Rectal Surgeons, Southern California Society of Colon and Rectal Surgeons, The American College of Surgeons and The American Medical Association. Dr. Hoffman’s main clinical and research interests involve the laparoscopic, minimally invasive treatment of colon and rectal malignancies. He has been published the peer-reviewed Diseases of the Colon and Rectum and Surgical Rounds.

Allen Kamrava, MD, ColorectalAllen Kamrava, MD

Allen Kamrava, MD is board-certified in Colon and Rectal surgery and is a colorectal surgeon at La Peer Health Systems and Los Angeles Colon and Rectal Surgical Associates, Inc. Dr. Kamrava’s clinical research interests include the care of patients with inflammatory bowel disease, advanced colorectal cancers, and complex anal diseases.He simultaneously received certification in advanced laparoscopic and robotic surgical techniques.

Benjamin Basseri, GastroenterologistBenjamin Basseri, MD

Benjamin Basseri, MD is a gastroenterologist who specializes in the evaluation and management of difficulty swallowing (dysphagia), indigestion (dyspepsia), abdominal pain, irritable bowel syndrome, inflammatory bowel disease, and colorectal cancer screening. Dr. Basseri is also an active member of the American Gastroenterological Association, American College of Gastroenterology, and American Society for Gastrointestinal Endoscopy.

David Magner Colorectal SurgeonDavid P. Magner, MD

Dr. Magner is board-certified in minimally-invasive and laparoscopic colon and rectal surgery. Through an interdisciplinary, patient-centered approach, Dr. Magner specializes in the treatment of all aspects of colorectal disease. Dr. Magner’s expertise includes pelvic floor dysfunction, benign anorectal conditions, advanced gastrointestinal malignancies, and inflammatory bowel disease.

Dr. Makhani, GastroenterologistMarc D. Makhani, MD

Dr. Marc D. Makhani is a gastroenterologist who is native of Los Angeles. Dr. Makhani centers his principles on a passion for promoting overall health and wellbeing. Dr. Makhani has a wide range of clinical and research interests that include colon cancer screening and prevention, motility disorders of the gastrointestinal tract, gastroesophageal reflux disease, peptic ulcer disease, irritable bowel syndrome and inflammatory bowel disease.

Marc Edelstein, GastroenterologistMarc Edelstein, MD, FACP, FACG

Dr. Edelstein is a board certified gastroenterologist with expertise in diagnosing and treating digestive disorders. He earned his medical degree from Boston University then completed and internship and residency in Internal Medicine at UCLA Medical Center. He also completed a Gastroenterology fellowship at UCLA Medical Center.  In addition to being a Diplomate of the American Boards of Internal Medicine and Gastroenterology, he has been elected a Fellow of the American College of Physicians and the American College of Gastroenterology.

Maziar Ghodsian, MD

Dr. Maziar Ghodsian, or Dr. Maz, as he is so kindly referred to by his patients, is a highly specialized Proctologist and Colorectal Endoscopist. He specializes in diseases of the colon and rectal surgery as well as aesthetic anal beautification and rejuvenation. Dr. Maz also performs diagnostic and therapeutic colonoscopies for colon cancer and rectal cancer.

Dr. Maz obtained his Bachelor of Science in Biology and a Minor in Philosophy from the University of California, Riverside. Dr. Maz continued his training at the Johns Hopkins University, where he received a second Bachelor of Science in Nursing followed by a Juris Doctor with a concentration on Healthcare Law and Policy from the Pace University School of Law. He then attended medical school at Western University of Health Sciences in Southern California and completed his internship at Arrowhead Regional Medical Center. Dr. Maz completed his residency training in Proctologic Surgery at Ohio University-Grandview Medical Center/Kettering Health Network in Dayton, Ohio. Additionally, Dr. Maz completed a portion of his residency training in Proctologic Surgery at the Cleveland Clinic Foundation and Cedars Sinai Medical Center with world renowned experts. Dr. Maz is a Board Member of the American Osteopathic College of Proctology.

Dr. Maz is one of only two practicing Proctologic Surgeons in California that have completed a residency in Proctology.

Using his specialized minimally invasive and aesthetic approach, Dr. Maz uses exceptional technical skills in treating his patients with both surgical and non-surgical treatment modalities. Dr. Maz is highly specialized in the cosmetic removal of anal skin tags, lesions, warts and hemorrhoids.

Contact Our Colonoscopy Experts

If you are nearing the age of 50 and need to schedule your first colonoscopy or need to schedule a second or third screening, contact our Los Angeles colonoscopy doctors. Additionally, our doctors can perform colonoscopies at Cedars Sinai Medical Center. If you are interested in seeing a Cedars Sinai colonoscopy specialist or would like to undergo Cedars Sinai colonoscopy, please feel free to contact our surgery center. You can reach our office by phone at or by filling out our online contact form. We look forward to providing you high quality patient care.

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