Human body weight different from body mass index
Fluctuation
Body weight varies throughout the day, as the amount of water in the body is not constant. It changes frequently due to activities such as drinking, urinating, or exercise. Professional sports participants may deliberately dehydrate themselves to enter a lower weight class, a practice known as weight cutting.Ideal body weight
Ideal body weight (IBW) was initially introduced by Ben J. Devine in 1974 to allow estimation of drug clearances in obese patients; researchers have since shown that the metabolism of certain drugs relates more to IBW than total body weight. The term was based on the use of insurance data that demonstrated the relative mortality for males and females according to different height-weight combinations.
The most common estimation of IBW is by the Devine formula; other models exist and have been noted to give similar results. Other methods used in estimating the ideal body weight are body mass index and the Hamwi method. The IBW is not the perfect fat measurement, as it does not show the fat or muscle percentage in one's body. For example, athletes' results may show that they are overweight when they are actually very fit and healthy. Machines like the dual-energy X-ray absorptiometry can accurately measure the percentage and weight of fat, muscle, and bone in a body.