The definition of obesity varies, depending on the method used to assess body composition. It is generally defined as being 20% over the recommended weight in height/weight. The problem with this criterion is that it incorrectly places the emphasis on body weight rather than body composition. Body mass index (BMI) measurements provide a better approach for classifying levels of fatness). Many experts use a BMI of 27 as a single value at which obesity occurs. The best methods involve actual body measurements. Body fat measurements of 25% for men and 32% for women are classified as moderately obese. , which provides six levels of body fat classification.

Regardless of which measurement technique is used, it is important to view body-fat assessment results as measures on a continuum. They are not precise points on a scale that when exceeded magically increase a person’s risk for health problems. For example, although 24.9% body fat for a man does not technically fall into the category of “obesity,” it is only one tenth of a percent removed from the “magic number” of 25 and for all practical purposes carries the same risk as someone who is classified as obese. Research on obesity shows that a man with 25% body fat should not view himself as crossing a line that somehow suddenly exacerbates his health risks more than his “non obese” peer who is at 24.9% body fat.

Causes of Obesity

The laws of thermodynamics state that energy cannot be destroyed; it is used for work or converted into another form. Accordingly the progressive accumulation of stored fat in the body is the result of consumption of more calories (energy) than are expended. Food energy in excess of the body’s need results in storage of fat in adipose cells. This relationship applies to almost all individuals. For the majority of people, excessive caloric intake and deficient energy expenditure are responsible for their obesity. What are more difficult to explain, however, are the differences in peoples’ responses to the laws of energy conservation and expenditure. Two people may be overfed the same number of calories and yet differ in the amount of weight gained, even if their activity levels are held constant. What accounts for these differences? The answer is not simple and suggests that obesity is a complex issue, involving both biological and behavioral theories.