Jules Hirsch was born in New York City and died at age 88 after a long illness. He was considered a notorious leader in the study of human metabolism, mainly in the area of lipids and obesity. His research at The Rockefeller University helped to establish the mechanism of obesity and lipid metabolism. Hirsch joined Rockefeller’s faculty in 1954 and remained there for the rest of his career. Hirsch’s research helped to support the idea of dynamic interactions among diet, physical activity, general metabolism and obesity. At that time, most scientists considered adipose tissue to be biologically inert, a passive insulator in which the body stored energy in the form of triglycerides. Another important contribution was to point out the relationship between diet and cardiovascular ailments, as well as metabolism disturbance. Hirsch had a natural characteristic of showing a nice smile and greeting for everyone he worked with at the university. Key words: Hirsch, diet, physical activity, obe