i disagree on this. if you have a strong willpower and are determined to get healthier, then your body will automatically be repulsed by fatty foods. however, subjecting yourself to constant torture at the gym will never be a fun activity (unless your goals are minimal).
Dietary fat isn't bad for you. You body has no regulation mechanic to avoid ingesting fat because it needs it to function.
Second, if it were easier to diet than exercise, the US would be full of skinny people with no muscle. Not fat people on treadmills.