A healthy diet is the key to being fit.Its more important to eat healthy since our weight doesn't define how healthy we are it all depends on the way we treat our body and this includes what we put into it. EAT HEALTHY,BE HEALTHY, AND LOSE WEIGHT FEEL GREAT=) OK
I think even if you have great genetics and sit on your lazy bum, your going to get fat. The fact is a combo of both produce someone who is in peak physical condition. The lazy bum who never tried is going to just get fat and nothing about his genetics is going to fix that.
A person may be predetermined and at risk for diseases such as heart disease, diabetes, and cancer. But I believe an predetermined individual can still prevent or less the severity of health conditions if they eat a healthy diet and avoid certain foods and certain foods just as it is beneficial to a unpredetermined person. A regular exercise routine is also beneficial to health.
Diet and exercise are certainly better determinants of health than genetics are. I would not have believed this a few years ago, until I started watching scientists do TED talks. You can actually change the behavior of your genes though diet and exercise, and turn a genetic predisposition into a strength.
I believe that diet and exercise are better determinants for health than genetics because you could come from a slim family and still be very overweight if you overeat and don't exercise. Diet and exercise control our daily lives and determine our future better than genetics. Unfortunately people blame genetics for bad health when it is really their diet and exercise causing it.