Studies have shown that how much you exercise does not necessarily decide what you weigh. There has been many different experiments and tests that were done to try to figure out why some people gain more than others if eating and exercising the same. Scientists everywhere do not understand why some people gain more. They are doing everything they can to figure out why this happens.
Researches recently found out that there is a gene in mice that acts in the brain and controls how quickly calories are burned. Scientists figured this out while running tests on mice. The scientists deleted the gene in some of the mice's brains. They left the genes in other mice. What they found out was shocking.
The mice were consuming the same number of calories as lean mice, but they were gaining weight. Some scientists believe that some humans have the same gene and maybe that is why they are overweight. People have always thought that genes had something to do with weight and now those people are proven correct. Weight can be inherited.
So far, only one person has been found to have a disabling mutation with that gene. That person is severely obese. People have long thought that your weight has to do with self-control. Having self-control has a little to do with your weight but it is mostly your genes that control your weight. If your parents are overweight, then it is in your genes to be overweight. Exercising and eating right will not make that much of a difference.
http://www.nytimes.com/2013/07/19/health/overweight-maybe-you-really-can-blame-your-metabolism.html?pagewanted=1&_r=0&hp