Body mass index (BMI) is a measurement based on height and weight as it relates to body fat, and can be used to determine how much risk a person has of developing certain health problems because of his or her weight. As a point of reference, someone with a BMI of 27 is approximately 20 percent overweight. The higher the BMI, the greater the risk a person has to develop additional health problems.

Your BMR, or basal metabolic rate (metabolism), is the energy (measured in calories) expended by the body at rest to maintain normal bodily functions. This continual work makes up about 60-70% of the calories we use (or expend) and includes the beating of our heart, respiration, and the maintenance of body temperature. Your BMR is influenced by a number of factors, including age, weight, height, gender, environmental temperature, dieting, and exercise habits. Because of the increased activity of cells undergoing division, the younger the person, the higher (faster) the metabolism. And the taller and heavier a person is, the faster their metabolism. Because of the greater percentage of lean muscle tissue in the male body, men generally have a 10-15% faster BMR than women. And when you go on restrictive, traditional diets, your BMR can drop by as much as 20%. People living in tropical or very cold environments generally have BMR's 5-20% higher than those living in more temperate climates. In general, depending on the intensity and duration, consistent exercise can also increase your BMR.