William Lustig is an American endocrinologist and professor known for his research on obesity and metabolism. He gained prominence for his work on the role of sugar and insulin in weight gain and chronic diseases. Lustig advocates for dietary changes to combat obesity and related health issues. In addition to his research, Lustig is a public speaker and author, having written books like Fat Chance: Beating the Odds Against Sugar, Processed Food, Obesity, and Disease. He has also produced documentaries that highlight the dangers of excessive sugar consumption and its impact on health.