William Sullivan, MD

William Sullivan, MD, is medical director of the Joslin Center for Diabetes and Endocrinology at Beth Israel Deaconess Hospital–Needham. He is also a senior endocrinologist at Joslin Diabetes Center. An assistant professor of medicine at Harvard Medical School, his main focus is the care of patients with diabetes, but he also is involved in caring for patients with other endocrine disorders, particularly thyroid disease. Prior to joining BID–Needham, he was an attending physician at Beth Israel Deaconess Medical Center in Boston, where he continues to see patients. At BID–Needham, Dr. Sullivan helped start a continuous glucose monitoring program for patients on intensive insulin therapy. A graduate of the Georgetown University School of Medicine, he completed his internship in medicine at Thomas Jefferson University Hospital, his residency at Wilford Hall USAF Medical Center, and fellowships in diabetes and endocrinology at Joslin Diabetes Center and Yale-New Haven Hospital.

Richard S. Beaser, MD

Richard S. Beaser, M.D., is a practicing physician in the Joslin Clinic and holds the position of Associate Clinical Professor of Medicine at Harvard Medical School. He has also been the Medical Executive Director of Professional Education at Joslin and was instrumental in developing that activity at Joslin, a department he founded in 1990. He currently serves as the Chair of the Continuing Medical Education Committee at Joslin Diabetes Center and is active in professional education as well as the care of people with diabetes.

Dr. Beaser has been on the staff of the Joslin Diabetes Center since 1982. He has held numerous past positions at Joslin, including Section Chief of the Adult Diabetology Practice, Medical Director of the Diabetes Treatment Unit, Coordinator of the Patient Education Section, and Medical Director of Joslin TrialNet, a clinical trials network. He has been a clinical research investigator, including the landmark Diabetes Control and Complications Trial.

Dr. Beaser has authored four books: Joslin Diabetes Manual, Outsmarting Diabetes, The Joslin Guide to Diabetes, and Joslin’s Diabetes Deskbook: A Guide for Primary Care Providers. Dr Beaser is a well-known national lecturer on clinical diabetes and its comorbidities. He is the author of numerous publications in peer review journals, review articles, and book chapters.

Natasha Kasid, MD

Natasha Kasid, MD has joined the Joslin Center for Diabetes and Endocrinology at Beth Israel Deaconess Hospital–Needham. Dr. Kasid is board certified in Internal Medicine and her clinical interests are general diabetes and diabetes in pregnancy. She graduated from Howard University College of Medicine in 2010 and finished her residency training in Internal Medicine at Dartmouth-Hitchcock Medical Center in 2013. Dr. Kasid completed her fellowship in Endocrinology, Diabetes and Metabolism at Beth Israel Deaconess Medical Center and the Joslin Diabetes Center.

Nurse Practitioner

Angela Kaptsan, MSN, BC-ANP, CDE

Angela Kapstan, MSN, BC-ANP, CDE, joined the Joslin Center for Diabetes and Endocrinology in 2011 as a nurse practitioner. Her medical interests include helping patients manage type 1 and type 2 diabetes, hypertension, hyperlipidemia and metabolic syndrome. In addition, she has more than 10 years of nursing experience in emergency medicine, having worked in emergency departments in Israel and Pennsylvania. Board certified by the American Academy of Nurse Practitioners, Ms. Kapstan received her bachelor's degree in nursing from Tel Aviv University and her master's at Wilmington University. Fluent in Russian, she was born in Ukraine and lived in Israel for seven years before coming to the United States.

Certified Diabetes Educators

Mary Paschal, RN, MS, CDE

Nurse Educator

For the past 20 years, Mary Paschal, RN, MS, CDE, has been a registered nurse and certified diabetes educator at the Joslin Center for Diabetes and Endocrinology. In addition, she is the Joslin Center program manager. She completed her undergraduate and graduate degrees at Boston College.

Marissa Bunnewith, MS, RD, LDN

Registered Dietitian

Marissa graduated from Johnson & Wales University with a bachelor’s degree in Culinary Nutrition, and an associate degree in Baking & Pastry Arts. During her undergraduate work, Marissa learned about all aspects of food and nutrition, how to take dietary restrictions and food preferences, and turn them into restaurant-worthy dishes. Before becoming a registered dietitian, Marissa worked as a head pastry chef on Nantucket and the kitchen management team for America’s Test Kitchen. Marissa earned her master’s degree in clinical nutrition from Rutgers University and completed her dietetic internship in 2020. There she completed an intensive supervised learning experience at University Hospital in Newark, New Jersey, including several ambulatory rotations at Children’s Specialized Hospital, DaVita Dialysis, and Care One. She even traveled to Greece to learn about the origins of the Mediterranean diet.

Marissa specializes in both acute care medical nutrition therapy and outpatient diabetes counseling. She focuses on meeting the client where they are, making small changes that lead to successfully meeting their goals. Marissa helps people figure out how to adapt their dietary restrictions to meals without compromising flavor and variety. She helps both new and practiced diabetes patients take control of their diets, taking the guesswork and complexity out of meal planning. Marissa has experience with nutrition counseling in those with prediabetes, type 1 and type 2 diabetes, cardiovascular disease, renal disease, weight management, digestive disorders, pregnancy, and tube feeding assessments.

Unit Coordinator

Ann McDonald

Practice Assistant

Nicole Monkman

Medical Assistants

Lisa Cohen
Alexis Shatz