The human body is a remarkable food processor. As an adult, you may consume over a ton of food per year and still not gain or lose a pound of body weight. You are constantly harnessing, and consuming energy through the intricate mechanism of your body in order to remain in energy balance. To maintain a given body weight, your energy input must balance your energy output. However, sometimes the overall energy balance is upset, and your normal body weight will either fall or increase .
　　The term body image refers to the mental image we have of our own physical appearance, and This can be influenced by a variety of factors，including how much you weigh and how that weight is distributed. Research has revealed that about 40 percent of adult men and 55 percent of adult women are dissatisfied with their current body weight. Similarly findings have also been reported at high school level，mainly with female students. At the college level, a study found that 85 percent of both male and female first year students desired to change their body weight. The primary cause of this concern is the value that American society is in general a society to physical appearance. Thinness is currently an attribute that females desire highly. Males generally desire muscularity. The vast majority of individuals who want to change their body weight do it for the sake of appearance: most want to lose excess body fat. while a smaller percentage of individuals actually want to gain weight.