Like many other medical conditions, obesity is the result of an interplay between environmental and genetic factors.[2][3] Studies have identified variants in several genes that may contribute to weight gain and body fat distribution; although, only in a few cases are genes the primary cause of obesity.[4][5]
Polymorphisms in various genes controlling appetite and metabolism predispose to obesity under certain dietary conditions. The percentage of obesity that can be attributed to genetics varies widely, depending on the population examined, from 6% to 85%,[6] with the typical estimate at 50%. It is likely that in each person a number of genes contribute to the likelihood of developing obesity in small part, with each gene increasing or decreasing the odds marginally, and together determining how an individual responds to the environmental factors.[7] As of 2006, more than 41 sites on the human genome have been linked to the development of obesity when a favorable environment is present.[8] Some of these obesogenic (weight gain) or leptogenic (weight loss) genes may influence the obese individual's response to weight loss or weight management.[9]