Like HowStuffWorks on Facebook!

How Fasting Works

Fasting for Weight Loss

One might think that avoiding eating would be a good way to lose weight, but is it healthy? Although there are many opinions on this subject, several things seem evident. Fasting can be effective for fairly quick weight loss. After all, eating less reduces the number of calories the body receives. Because we use the calories in the food we eat for energy, once the body stops taking in more calories it starts using up its stored fat deposits.

But that doesn't mean that fasting is a good way to lose weight. Studies have shown that people who fast sporadically -- a few days here, a few days there -- generally put the weight back on when they go back to their usual way of eating. Thus, fasting is effective for quick, temporary weight loss, but does not work as a long-term weight loss solution. Modern medicine has also repeatedly found prolonged fasting to be unhealthy for the human body. Not eating causes blood sugar levels to drop. That, in turn, can lead to above-mentioned headaches, dizzy spells, nausea and disorientation. Fasting decreases one's metabolic rate; in other words, the body realizes that it's being starved and tries to conserve energy and calories. After the fast is over and you go back to regular eating habits, the hormones that regulate your appetite may push you to eat more [source: WebMD].

More importantly, fasting for prolonged periods of time is not considered safe. The reason for that is the fact that the body needs various vitamins and minerals to function and stay healthy. Without these minerals, you'll probably feel tired and dizzy, and you may have trouble fighting off colds.

In the next section, we'll take a more in-depth look at the various effects of fasting.