If you were an active person before Ideal Protein, after the first 3 weeks or so you can go back to some exercise. The diet is so low calorie, that you will need to add an extra packet within 1/2 hour of finishing exercise, to give your body fuel for recovery. The most important thing is to pay attention to what your body is telling you - if you feel overly fatigued, dizzy, etc...that's a sign to dial down the intensity. Some have been able to exercise at higher levels of intensity while on IP, but as many have found that doing more than light exercise stalls their weight loss. You can't improve the results of IP by adding exercise, but if it's something you enjoy or if you want to work on flexibility/toning while losing the weight, try it out.