1950, Coleman of the United States first discovered an obesity-related recessive factor (OBASE) in mice, which connected the circulatory system of obese mice with that of normal mice, and as a result, obese mice lost weight. This suggests that obese mice may lack some substance to regulate their weight. When it is connected with normal mice, it is supplemented from normal mice, so obesity is suppressed. Normal mice carry OB factor, which exists in adipocytes. It is found that daily intake of OB protein extracted from OB factor can reduce body weight, fat content, food intake and plasma glucose and insulin concentrations.

In the efficacy test of OB protein, the weight of mice treated with OB protein decreased by more than 50% compared with untreated mice. This shows that OB protein can not only reduce the food intake of rats to lose weight, but also reduce weight by increasing animal activity and accelerating metabolism.

OB protein is now named leptin, which comes from leptos—— in Greece-thin.