What You Need to Know About Exercise
If exercising regularly is already part of your life, when you first start intermittent fasting, you may need to modify your workout routine — hunger from intense workouts will make it much harder to stick to your plan.
If you're used to hitting the gym in the morning, fasted workouts might "feel hard at first," Precision Nutrition coach and fitness trainer Austin Lopez, CSCS, told POPSUGAR. This is especially true if you usually eat before a workout and if your workouts are vigorous, "but your body gets used to it," he said, and soon you may even prefer it.
On the other hand, working out while fasted might make you feel super tired and unable to go as intense as you want, warned Kellilyn Fierras, MS, a registered dietitian, NASM-certified personal trainer, and instructor at EverybodyFights in Boston. If that's the case, listen to your body, and shift your workouts to a time during your eating window instead.
Or you might find exercise is too difficult to do at all when you first start intermittent fasting. So focus on getting your IF schedule established, which might mean putting your workouts on hold, doing easier forms of exercise, or changing the times you work out to suit your IF schedule. Gradually work up to your regular workout routine; this shouldn't take more than a few weeks.