Nutritional disorders Obesity
Storage of lipids in excess of daily requirements results in obesity - an excess of adipose tissue that is associated with a health risk. Obesity is defined as a 20% excess over ideal body weight and in many Western populations 30-40% of individuals are obese. Most obese individuals ingest excess calories that are then stored. The reasons for overeating are not clear, but they may involve psychosocial factors that modulate the activity of the satiety centre; this may be coupled with reduced calorie expenditure resulting from a sedentary existence, or with alterations of thermogenesis. In a small number of cases, obesity is secondary to diseases such as hypothyroidism, Cushing's syndrome and extremely rare disorders such as insulinoma.
The end result of excessive calorie intake is an increase in fat deposition around the internal organs and muscles, and in subcutaneous sites such as abdomen, buttocks, breasts, thighs, face and upper arms. Such obesity is associated with insulin resistance and glucose intolerance, hyperlipidaemia, hypertension and an increased incidence of thrombotic arterial and venous disease and of degenerative joint diseases. Weight reduction towards the norm is associated with improved life expectancy.
Tables of desirable weights are available for age, sex and height. A more acceptable and accurate assessment method is to use the Body Mass Index (BMI), which is calculated as weight in kilograms divided by height in metres squared. BMI values of 19-24 in women and 20-25 in men are associated with the longest life expectancy. Values over 30 (obese) and over 35 (morbidly obese) are associated with significant reduction of life expectancy. The problem is that BMI does not differentiate between upper and lower body fat distribution.