He is professor emeritus of pediatrics in the division of endocrinology at the University of California, San Francisco (UCSF), where he specialized 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.

[2] Lustig's publications discussed a proposed toxic effect of dietary fructose – a component of sucrose (table sugar), honey, fruit and some vegetables – on the development of obesity.

[13][14] Excessive consumption of fructose-containing beverages is likely a cause of weight gain and obesity in many people due to the additional caloric intake rather than a specific toxic effect of fructose.

[13][15][16][17][18] Fructose – when consumed in excess as a sweetening agent in foods and beverages – is associated with surplus calories and greater risk of obesity, diabetes, and cardiovascular disorders as components of metabolic syndrome.