flatbusher – The Pasuk refers to Guarding your body from Danger. Smoking and overeating may kill you after years of doing it but getting hit by a car can kill you instantly, so you can fulfill the pasuk by crossing at the crosswalk with a green light and looking both ways.
The vast majority of Jews are not smokers so they don’t fulfill it by not smoking. Otherwise everyone should get credit for not eating ham. As far as excising in order to combat overweight, that too is dangerous look at all the medical emergencies during marathon races. Being overweight causes the heart to work harder resulting in heart problems. So Rav Moshe answer concerning smoking, of G-d watches out for the fool applies to overweight too.
Other examples of fulfilling this pasuk are wearing a seat belt while driving, not speeding, not talking on the phone while driving.