Obesity is a global epidemic and one of the major health burdens of modern times. The prevalence of obesity is increasing worldwide; it constitutes a serious problem in developed as well as developing countries. Beside adults, the number of obese teenagers and children in particular has dramatically increased. Obesity is characterized by accumulation of excess fat in adipose tissues in an extent to produce adverse effects on health, leading to a reduction in life expectancy and/or a raise in health hazards. People are classified as overweight (pre-obese) and obese on the basis of the Body Mass Index (BMI), crude measure which compares weight to height. Obesity is usually associated with and can lead to many disease conditions, mainly type-2 diabetes, cardiac diseases, hypertension, sleep apnea, cerebrovascular incidents, osteoarthritis and certain types of cancers. The tremendously increasing number of reviews on the subject of obesity obviously reflects the amount of investigations currently dedicated to this field. The core of obesity treatment is dieting and physical exercise. The consumption of energy-dense food is reduced versus an increase in that of dietary fibers. Conventional medication relies mainly on drugs which either reduce appetite or inhibit fat absorption. However, drug treatment of obesity despite short-term benefits, is often associated with undesirable harmful side effects, rebound weight gain after discontinuation of drug intake, and the incidence of drug abuse. If diet, exercise and pharmacological therapy are ineffective; surgical intervention may be useful. The anti-obesity potential of natural products if accurately explored might provide an excellent alternative strategy for the scientifically-based development of safe and effective drugs. Especially that, they are actually widespread for this purpose as nutritional supplements. OTC anti-obesity natural products are mostly complex in terms of chemical composition and may exert a variety of pharmacological actions leading to weight loss. These include: inhibition of lipases activity, suppression of appetite, stimulation of energy expenditure, inhibition of adipocyte differentiation and regulation of lipid metabolism. A variety of natural products, including crude extracts and isolated compounds induce body weight reduction and prevent diet-induced obesity. Examples of these constituents are polyphenols, triterpenoidal and steroidal saponins, pregnane glycosides, alkaloids, abietane diterpenes and carotenoids amongst others. In addition, a number of lipase inhibitors are obtained from microbial sources.
The present chapter is intended to survey the vast array of natural products from plant and microbial origin currently suggested as conventional drug alternatives for management of obesity. This will cover the natural sources, extracts, safety assessment and structures of bioactive compounds, as well as the biochemical markers used to evaluate the anti-obese effect and/or determine the mechanism of action. New drug targets that may play a role in the regulation of body weight will also be considered.