The fat cell, the functional entity of adipose tissue, is mainly involved in energy storage and mobilization. The deposition of fat in, and the mobilization of fat from, adipose tissue are precisely controlled by enzyme activities: LPL and HSL. These functions are under control of hormones such as insulin, catecholamines and, to some extent, steroid hormones. The adipocytes have been recently identified as the source of many factors that may act like hormones either in the local environment or at distant sites, are also target cells for many more hormones. Adipose tissue metabolism varies from one region of the body to another. The metabolic activity is the lowest in the subcutaneous gluteofemoral area, followed by the abdominal subcutaneous area, and the highest in the visceral region. The metabolic activity of gluteofemoral fat is activated in lactating mothers. Body fat content changes with female age. Puberty, parity and menopause seems to increase accretion of adipose tissue. Obesity is defined as an increase in body fat content. There is general agreement that obesity develops as an interaction between a genetic susceptibility and environment which is expressed when the subject is exposed to a certain set of environmental conditions. Obesity develops when energy intake exceeds energy expenditure over a prolonged period. Excess body weight is associated with several diseases which can shorten life expectancy. The prevalence of obesity is high and increases steadily. Approximately 20-40% of women are overweight (BMI 25-30 kg/m-2) and 5-20% are obese (BMI > 30 kg/m-2).