Robert H. Lustig (born 1957) is an American pediatric endocrinologist. He is Professor of Pediatrics in the Division of Endocrinology at the University of California, San Francisco (UCSF), where he specializes in neuroendocrinology and childhood obesity. He is also director of UCSF's WATCH program (Weight Assessment for Teen and Child Health), and president and co-founder of the non-profit Institute for Responsible Nutrition.

Lustig came to public attention in 2009 when one of his medical lectures, "Sugar: The Bitter Truth," became popular on YouTube. He is the editor of Obesity Before Birth: Maternal and Prenatal Influences on the Offspring (2010), and author of Fat Chance: Beating the Odds against Sugar, Processed Food, Obesity, and Disease (2013).