A study in the Journal of the American Medical Association followed the exercise habits of more than 34,000 women and concluded that it took about an hour a day of moderate exercise (walking at 3mph) to maintain weight.” (1) This study did not mention anything about LOSING weight.
That’s because your body is finely tuned to adjust to the workload you give it. If you run at the same pace every day for 1 hour, your weight loss potential drastically decreases after only one week. Your body gets used to what you do to it.
If, however, you focus more on the intensity of your workout rather than the duration of your workout, you can see more significant results in losing fat. “Researchers at the University of Western Ontario compared short but intense exercise to long, less-intense cardio. One group performed four to six 30-second "sprints" while the other group did cardio for 30 to 60 minutes. The results were nothing short of amazing. Despite exercising for a fraction of the time, those in the sprint category burned more than twice as much body fat.”(2) Basically, if you workout shorter but harder, you can effectively burn fat.
It is also noteworthy to mention that if you are running for 2-3 hours a day, you may even gain weight! This is because cortisol, a stress hormone, is released during exercise. A small amount of cortisol is ok, however, if you are working out so much that you release large amounts of cortisol, you throw off hormonal balance and you can even gain weight. If you push yourself TOO much, you can even suppress thyroid function and ultimately decrease your metabolism.
So what CAN you do to lose weight? When it comes to running, choose burst training routines no more than 20 minutes. Choose to work harder for a shorter period of time. Mix cardio training with weight resistance training in order to increase muscle mass. These two types of exercise (interval training and weight training) increase muscle and therefore maintain your metabolism higher for longer. Basically, your body will burn more calories at rest than before. So, when it comes to running, work smarter, not longer. Your body will thank you for it.