1. Exercise sometimes gives you a false sense of being on track on your diet. Wow, that was an amazing twenty minute walk I just went on - I think I can afford to eat that Snickers bar now!
2. If you increase your metabolism significantly through exercise then you might be in a dieting pickle if you have to stop. Injuries do happen and every year I can remember we do have a NH winter!
3. Too much exercise at one time can starting eating away at your muscles rather than just your fat. This is never a good thing!