ABSTRACT
Adipose tissue is a highly specialized organ dealing mainly with processes for storage and release of energy. The underlying metabolic routes of these processes are regulated by a complex network to meet the energy requirements of the body. In times of a positive energy balance, i.e., energy (food) intake exceeding energy requirements, excess energy is stored as fat. In times of a negative energy balance, i.e., energy requirements exceeding energy intake, including the extreme situation of long-term fasting, fat resources are mobilized. Both processes operate in a highly efficient manner to prevent wasting of energy and to ensure survival of the organism. Adipose tissue has a highly adaptive capability for storing large amounts of fat. This can be achieved by increasing fat cell size or fat cell number (see also chapter 1 0 of this volume). Normally, a human subject has about 1 0 to 20 kg of body fat. Taking into account a caloric value of about 7 , 0 0 0 kcal per kg fat tissue, an energy reserve of 70,000 to 140,000 kcal (that is 300-600 MJ) is stored in adipose tissue. The caloric value for adipose tissue is lower than that for pure fat, i.e., triglycerides (about 9 ,0 0 0 kcal per kg) because the fat-storing adipocytes are normally not completely catabolized for generation of energy. Body fat mass can increase tre mendously (between 40 to 1 0 0 kg or more) and this accumulation of excess body fat is called obesity. Obesity is by no means an appearance of the late 2 0 th and the early 2 1 st century. One of the first reports of obesity is the “Venus of Willendorf”, a small statuette showing clear signs of abdominal obesity. 1 Obesity has been found in almost all old medical traditions including Egyptian, Chinese, Indian, Meso-American, Greco-Roman and Arabic medicine and there have been already single reports about treating obesity as a disease. 1 However, in all these traditions occurrence of obesity was limited to the “higher classes” . 1
It was the merit of Vague et al2 to show that not obesity per se but abdominal rather than gluteo-femoral body fat accumulation predisposes to obesity-associated diseases such as dyslipidemia, hypertension, diabetes mellitus, or arteriosclerosis-a complex known also as metabolic syndrome.2 This was the first indication of an obvious functional heterogeneity of adipose tissue depending on the location within the human body. With respect to anatomic location, different regions of white adipose tissue can be distinguished as listed in Table 8 . 1 .
