Hi Kathy,
Alli's plan is designed to control and maximize calories, while not placing extreme restrictions on your diet. You should be fine to execute the workouts, but let your body tell you if you need to supplement or adjust your diet in any way. If you are too fatigued or feel that you dont have enough energy to get through your workouts effectively, you may need to suppplement with a well-timed, nutritious, low-fat snack. If you need more calories to fuel intense workouts, your body will give you signs. You may also want to speak with the online dietician to be sure you're not over or under-doing it.
For now, give the workouts your all and stick with your eating plan and the pills as recommended.
Good Luck,
Paul