| 1978-1979 | Assistant Professor of Medicine, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA. |
| 1980-1987 | Assistant Professor of Medicine, Columbia College of Physicians & Surgeons, New York, NY |
| 1982- | Faculty Member, Institute of Nutrition of Columbia University |
| 1987-1993 | Associate Professor of Clinical Medicine, Columbia College of Physicians & Surgeons, New York, NY |
| 1993- | Adjunct Associate Professor of Nutrition and Education, Columbia Teachers College, New York, NY |
| 1994-1998 | Associate Professor of Medicine, Columbia College of Physicians & Surgeons, New York, NY |
| 1998 | Professor of Medicine, Columbia College of Physicians & Surgeons, New York, NY |
| 1978-1979 | Staff Physician, Philadelphia Veterans Administration Hospital, Philadelphia, PA |
| 1979-1986 | Assistant Attending Physician, St. Luke's-Roosevelt Hospital Center, New York, NY |
| 1986- | Associate Attending Physician, St. Luke's-Roosevelt Hospital Center New York, NY |
| 1989- | Director, Section of GI Immunology, Gastrointestinal Division, St. Luke's-Roosevelt Hospital Center New York, NY |
| 1991- | Associate Chief, Gastrointestinal Division, St. Luke's-Roosevelt Hospital Center New York, NY |
| 1997- | Senior Attending Physician, St. Luke's-Roosevelt Hospital Center New York, NY. |
| 2000- | Director, Gastrointestinal Division, St. Luke's-Roosevelt Hospital Center New York, NY |
| 2000- | Director, GI Training Program, St. Luke's-Roosevelt Hospital Center New York, NY |
| 2000- | Director, GI Endoscopy Unit, St. Luke's-Roosevelt Hospital Center New York, NY |
| 1965-1969 | Dean's List |
| 1968 | Phi Beta Kappa |
| 1968-1969 | Henry Rutgers Scholar in Physiology |
| 1969 | Oakley Van Der Poole Award in Microbiology |
| 1973 | Alpha Omega Alpha |
| 1978 | Third Prize, Komarov Competition |
| 1982 | Named in Who's Who in Frontier Science and Technology |
| 1984 | Named in Who's Who in the East |
| 1984,1989,1992 | Selected as participant in Citizen Ambassador Program by People to People International |
| 1987 | Visiting Professor, Boston City Hospital, Boston,MA |
| 1988 | Named in American Men and Women in Science |
| 1988 | Named in International Leaders in Achievement |
| 1988 | Visiting Professor, Temple University, Philadelphia, PA |
| 1988 | Fellow-American College of Nutrition |
| 1989 | Named in Who's Who of Emerging Leaders of America |
| 1991 | Visiting Professor Westminster Hospital, London, England |
| 1991 | Visiting Professor Yale University, New Haven, CT |
| 1991 | Named in New York Magazine's, Best Doctors in New York |
| 1992 | Visiting Professor, University of Texas, Houston, Texas |
| 1993 | Visiting Professor, University of Pennsylvania, Pennsylvania, PA |
| 1993 | Named in Who's who in Science and Engineering |
| 1993 | Visiting Professor, SUNY Upstate Health Center, Syracuse, NY |
| 1993 | Visiting Professor, University of Wisconsin, Milwaukee, WI |
| 1994 | Visiting Professor, University of Cincinnati, Cincinnati , Ohio |
| 1996 | Visiting Professor, Medical College of Virginia, Richmond, Virginia |
| 1997 | Named in New York Magazine's, Best Doctors in New York |
| 1997 | Named in Who's Who in Medicine and Healthcare |
| 1998 | Visiting Professor, Graduate hospital, Philadelphia, PA |
| 2001 | Named in Castle Connolly America's Top Doctors |
| 2001 | Named in Castle Connolly Top Doctors: New York Metro Area |
| 2002 | Named in Best Doctors of America |
| 2003 | Visiting Professor, Brown University, Providence, RI |
| 2004 | Visiting Professor, The Mount Sinai Hospital |
| 1981- | Research Associate, Obesity Research Center, St. Luke's-Roosevelt Hospital |
| 1982-1986 | Gastroenterology Consultant, Columbia University Student Health Service, New York, NY |
| 1982- | Member, Bioengineering Institute of Columbia University |
| 1987-1992 | Member - AIDS Clinical Treatment Group, St. Luke's-Roosevelt Hospital |
| 1988-1989 | Member - National Task Force on Nutrition in AIDS |
| 1988-1990 | Member - Scientific Advisory Board, Community Research Initiative, NYC |
| 1989- | Research Associate, Brookhaven National Laboratories, Upton, NY |
| 1989-1991 | Ad hoc member - NIH Study Section, AIDS Expedited Review Study Section |
| 1990-1991 | Co-Chair - Enteric Parasite Pathogen Study Group, ACTG, NIAID |
| 1990-1995 | Member - Nutrition Committee, Physicians Association for AIDS Care |
| 1990-1991 | Member - Advisory Board, Visiting Nurse Service of New York |
| 1991 | Member - Advisory Group for GI Infections, World Congress of Gastroenterology |
| 1991-1996 | Member - Editorial Board, American Journal of Gastroenterology |
| 1991- | Member - Board of Directors, Community Research Initiative on AIDS, New York, NY |
| 1992-2001 | Trustee - Royal Marks Foundation |
| 1993- | Medical advisor, Treatment Action Group |
| 1993-1995 | Trustee - Physicians Association for AIDS Care |
| 1994- | Member Editorial Board - Journal of Parenteral and Enteral Nutrition |
| 1996- | Vice President - Board of Directors, Community Research Initiative on AIDS, New York, NY |
| 1997-2000 | American Gastroenterological Association Clinical Teaching Project |
| 2000-2002 | International AIDS Society USA Committee on Treatment Guidelines for HIV Lipodystrophy |
| 2001 | Office of AIDS Research, National Institutes of Health, Etiology and Pathogenesis Planning Committee |
| 2001-2003 | Member, Board of Directors, National Center for the Study of Wilson's Disease |
| 2001-2003 | Member, Medical Advisory Board, Wilson's Disease Association of America |
| 2002- | IAS-USA Core faculty |