Obesity is caused by complex interaction of genetic and environmental factors. It is difficult to determine if genetics play a dominant role or environmental factors play the dominant role in causation of obesity. In general a favorable environment and a genetic susceptibility interact to cause obesity.

The actual causes of obesity are still not clear despite tremendous development in medical science, including understanding of molecular pathways which regulate energy balance in humans, an essential component in pathogenesis of obesity. The cause obesity seems to be simple, such as chronic and excess consumption of food (calories) than expenditure of energy. But this theory of chronic excess nutrient intake relative to the level of energy expenditure does not hold in every obese individual, which proves that there are several other causes of obesity than simple consumption of excess food than we need.

Genes vs. Environment in Obesity:

The most important consequence of obesity is increased risk of death. Obesity is one of the leading causes of health problems. Obesity is responsible for higher morbidity and mortality. The risk of death from all causes is approximately 100% higher in compared to a normal weight individual. Obesity and overweight (BMI of 25-30) is leading cause of preventable death throughout the world, including in underdeveloped and poor countries. Obesity is responsible for more than 300,000 deaths annually in United States alone. The life expectancy of moderately obese individual is 2-5 years less than normal individuals and much lesser in highly obese individuals.

The important consequences (complications) of obesity include development of insulin resistance and type-2 diabetes, different cardiovascular diseases, respiratory diseases, increased incidence of gall stones, increased incidence of cancer, reproductive disorders, diseases of bones and joints etc.