As logical as it seems that being overweight or obese is associated with one’s metabolism, it is for the most part an urban legend or myth. With the exception of people who suffer from an under-active thyroid gland or hypothyroidism, it is quite uncommon for individuals to be overweight because of a sluggish metabolic rate. Generally, hypothyroidism is not a prevalent condition amongst the morbidly obese and overweight.

Nevertheless, a medical evaluation may determine the contributing factors behind weight gain. An individual’s basal metabolic rate is measured according to their lean body mass. In the body, muscle tissues are supported by burning more calories than are expended to sustain fat. In other words, muscles burn more calories than fat does. Moreover, lean body mass is impacted in three ways: body size, sex and age.

For the most part, overweight people carry between 20-35 percent of excess weight as lean tissue. For instance, when an individual packs on the pounds, not only is weight gain experienced in the body, but fat is increased in lean tissue so that it can support the fat. Dissimilar to the belief weight gain lowers the metabolism; the basal metabolic rate is increased because of the expansion of the lean tissue devised to support the body's fat.

In the realm of the genders, men usually have a higher caloric intakes and basal metabolic rates than women require. It is based on their biological make-up. After adulthood is reached, the body’s metabolic rate decreases by 2 percent every 10 years. As the body ages, hormonal levels coupled with the body’s composition shift. With the diminution of lean muscle mass, the loss is replaced by fat.

Weight loss begins with gauging one’s body’s caloric needs. There are a couple of ways to determine an individual’s sedentary caloric needs. While certain calculations are more accurate than other formulas, the most precise method for measuring the basal metabolic rate is used at healthcare facilities. The measurement is assessed by using a technique that measures the oxygen consumption.