Another myth that seems to have gripped the popular consciousness is that exercise is the key to weight loss. In no uncertain terms: THIS IS WRONG.
I bring this up because well-educated colleagues in the Physics department have made this mistake multiple times recently. These are people that with a few salient facts could calculate a rough estimate of the energy expenditure involved in a particular exercise and would promptly realize the absolutely trivial amount it represents. I have heard a tenured professor excuse digging into the cookie jar because he went to the gym yesterday.
As calculated here you would need to do an entire year’s worth of bench pressing in order to burn one pound of weight. The energy expenditure of an actual intense weightlifting session is probably no more than 200 calories, the equivalent of not drinking that soda with dinner. Don’t drink a sugary soda that is probably bad for you beyond its calorie count or spend a grueling hour in the gym? I know which one I will take every time.
Another problem is that overtraining is a very real problem with sometimes antithetical results. According to that study, doing moderate amounts of cardio actually yielded better results in terms of fat loss.
My suggestion then is to determine your goals. Realize that fat loss is best done through diet and do exercise to push in that direction but mostly for your health.