This is similar to the stress your body undergoes when you hit the gym. While exercising, that is a form of stress your body endures. As long as you give your body enough time to recover afterward, it will do your body good. The same applies for intermittent fasting — as long as continue to alternate between regular eating habits and fasting, it will continue to benefit you[*].
Side effects of fasting include dizziness, headaches, low blood sugar, muscle aches, weakness, and fatigue. Prolonged fasting can lead to anemia, a weakened immune system, liver and kidney problems, and irregular heartbeat. Fasting can also result in vitamin and mineral deficiencies, muscle breakdown, and diarrhea. When you drink laxative concoctions during a fast, there is an increased risk of fluid imbalance and dehydration.
Suprisingly, though, fasting may be a good idea. A recent review by Stephen Anton and colleagues, in the journal Obesity, found that intermittent fasting may come with a variety of health benefits, including reducing inflammation, improving the ratio of lean tissue to fat, improving cognitive function, preventing type 2 diabetes, and possibly even prolonging life span.
There are some downsides, however. As she explains, "By day two you may as well have all your calls forwarded to the toilet because you will be spending a lot of time in the bathroom. The first time I did the cleanse, I was out with my kids at the mall when all of a sudden I needed a bathroom, stat! It was a nightmare, trying to pack everyone up and find the restroom. I learned the mall is not the place you want to be when your body starts trying to eliminate toxins."