The Dangers of Fasting

Fasting has been around for thousands of years. It has been used to cleanse the body, lose weight and as part of religious ceremonies. In modern times, it is often used for weight loss alone. While short-term fasting for a day or so will not usually cause harm, your body will react by slowing the metabolism and, eventually, turning to muscle for nutrients. Prolonged fasting can be harmful to your body. Consult a doctor before beginning any type of fast.

How It Works

Fasting is usually done by refraining from eating and drinking only water for a set period of time, although there are some fasts that include drinking juices. In the first day of a water fast, your body turns to the stores of glycogen in the liver for calories, which breaks down to glucose. This usually runs out after the first 24 hours, and the body turns to its reserves of fat and protein to support most of the body, and the muscles to support the brain and red blood cells. After the third day, the body has used up all its reserves of glucose, and starts creating what's known as ketone bodies in the liver. The body can use them for fuel and it spares the muscles from wasting away. This process, known as ketosis, will continue as long as the body has enough fat stores. If you consume juices during the fast, some of this is mitigated due to the glucose in the juice.

Dangers

In addition to the side effects that can commonly occur as the result of fasting, such as dizziness, headache, nausea, muscle aches and anxiety, there are more serious problems that can arise. If you fast too long, your body may go into starvation mode, which can lead to anemia, hypoglycemia -- low blood sugar, and electrolyte imbalances that can lead to cardiac arrest and coma, according to Michael Picco at Mayo Clinic.com. Kidney and liver failure can also occur. Some people have died from prolonged fasts, usually because they were in a weakened state before fasting.

Who Should Avoid Fasting

There are certain instances where fasting is discouraged or should be limited to one or two days. If you are sick with a fever or fatigue, it is best not to fast. People with serious illnesses, such as cancer or AIDS, should avoid fasting. Those with kidney issues, diabetes or who are on prescription medications should not fast. Infants, women who are pregnant and those who have liver problems or anemia are at risk when fasting as well.

Considerations

For most people, fasting for 24 to 48 hours is not harmful although there are exceptions. It's best to consult a doctor before beginning any fast. If you are fasting to lose weight, realize that your weight loss will most likely be temporary. In addition, your body will go into starvation mode if you fast too long, and your metabolism will slow to conserve energy, meaning you won't burn as many calories. Prolonged fasting can often lead to binge eating once the fast is done, and many people gain any weight they lost back quickly.