Obesity is diagnosed when the patient’s BMI is greater than 30 kg m–2 (MarginNote 10.3). It is characterized by an excess of fat in the body, particularly underthe skin and is generally recognizable when a person is 20% above their IBW. Environmental and genetic factors can determine body weight, but overeating combined with lack of exercise are its usual causes. Very rarely, obesity may be secondary to endocrine disease , for example hypothyroidism that decreases energy requirements, Cushing’s syndrome where the distribution of body fat is altered, and some hypothalamic disorders that are associated with overeating.
A number of diseases occur more frequently in obese individuals (Figure10.25), including type 2 diabetes mellitus , coronary heart disease,hypertension , cholelithiasis and osteoarthritis . Not surprisingly, mortality rates are also greater as body weight increases. Some of the complications of obesity are listed in the Table 10.7.
The increasing incidence of obesity in many developed countries (Figure10.26 (A)), and particularly in children of the USA and UK (Figure 10.26 (B)),is of concern.