The words obesity and overweight are generally used interchangeably. However, according to the Institute of Medicine report, their technical meanings are not identical. Overweight refers to an excess of body weight that includes all tissues, such as fat, bone, and muscle. Obesity refers specifically to an excess of body fat.

It is possible to be overweight without being obese, as in the case of a body builder who has a substantial amount of muscle mass. It is possible to be obese without being overweight, as in the case of a very sedentary person who is within the desirable weight range but who nevertheless has an excess of body fat. However, most overweight people are also obese and vice versa. Men with more than 25 percent and women with more than 30 percent body fat are considered obese. The USFDA has released a chart detailing recommended weights relative to height; women should be in the lower end of their appropriate weight range, according to the chart.