"When glycogen is in short supply, your body also reverts to breaking down protein -- your muscles' building blocks -- for fuel," Pritchett says. So, while you may shed more fat when exercising on an intermittent fasting diet, you may lose more muscle, too. If you're heading out on a long run, but haven't eaten any carbs, your body might start burning protein within a couple of hours.
That won't just thwart how much weight you can bench press or how toned your butt looks. It will also slow your metabolism, which can make losing weight more difficult in the long run. In an effort to prevent starvation, your body adapts to the number calories you give it. So if you're frequently making drastic cuts to your calorie intake, your body will eventually adjust, burning fewer calories per day to ensure you have enough energy left to stay upright, breathing and healthy, Pritchett says.
In one small study from the Pennington Biomedical Research Center, after a group of men and women fasted every other day for 22 days, their resting metabolic rates (how many calories they burned each day by simply living), had dropped by 5%, or 83 calories. That's not exactly ideal for any exercise plan that's supposed to end in weight loss.
You can do an intermittent fasting diet and exercise, too, without hurting yourself. But you have plan carefully.
www.cnn.com