The increasing prevalence of obesity in many developed countries contributes to major adverse effect on public health.  The search for genetic and environmental factors that contribute to the epidemiology of obesity has led to the discovery of genes that regulate food intake and body weight. Obesity is defined as having very high amount of body fat in relation to lean body mass, or body Mass Index (BMI) 30 or greater. BMI is defined as the ratio of body weight in kilograms to square of height in meters. Obesity can be defined in absolute or relative terms. Assessment of obesity involves using three key measures: body mass index (BMI), if greater than 30, waist circumference, if greater than 40 inches. According to the World Health Organization: Obesity has reached epidemic proportions globally there are more than 1 billion overweight adults, at least 300 million of them obese. The levels of overweight adults worldwide will rise to 2.3 billion by 2015 and more than 700 million of them obese.  An estimated 22 million children under five are estimated to be overweight worldwide. Obesity accounts for 2-6% of total health care costs in several developed countries; some estimates put the figure as high as 7%. The true costs are undoubtedly much greater as not all obesity-related conditions are included in the calculations.

Multiple pathways including peripheral and central hormones and neurotransmitters are involved in regulation of food intake and body weight.