Why do I stay thin regardless of what I eat?

They all boil down to the same question, which is what underlies the differences between human beings between their body weight trajectories throughout life. In other words, why do some people remain thin while other people become fat. Obesity is terribly simple. There are just two sides to the equation and that's energy in, that is how much you eat, and energy out, how much you expend. So really we all know the answer, and that's that one side is greater that the other. The paradox is that it's very difficult to accurately measure energy in and energy out in any one individual throughout their life. You only need a tiny disturbance on a day-to-day basis, such as a half finger of twix too much every day for thirty years, and that can add up to 20 kilograms of weight. Our ability as scientists to measure each individual is difficult, especially when we try to take into account what people perceive as stuffing themselves. Ken's idea of stuffing himself might be nothing in comparison to my idea of stuffing myself, and I'm a big guy! Our research suggests that genetics is an underestimated factor. Body weights tend to run in families very strongly, and those genetic differences may affect the same parts of the brain that we talked about when we were saying about leptin hitting the brain. Our research is indicating quite strongly that it's variation in those parts of the brain might control both what you want to eat and in some cases, what you want to expend. If we can understand those, then perhaps we can manipulate them.