diet is main factor that cause obesity

As societies become increasingly reliant on energy-dense, large portion, fast-food meals, the association between fast food consumption and obesity becomes more concerning. In the United States consumption of fast food meal has tripling and calorie intake from fast food has quadrupled between 1977 and 1995.

Agricultural policy and techniques in the United States and Europe have led to lower food prices. In the United States, subsidization of corn, soy, wheat, and rice through the U.S. farm bill has made the main sources of processed food cheap compared to fruits and vegetables.

There is little evidence to support the commonly expressed view that some obese people eat little yet gain weight due to a slow metabolism. On average obese people actually have a greater energy expenditure than thin people. This is because it takes more energy to maintain an increased body mass. What has been found is that obese people under report how much food they consume compared to those of normal weight. Tests of human subjects carried out in a calorimeter support this conclusion.