Fasting has its benefits, research shows, but there is plenty of information to know ahead of time to make sure it's done safely.
With a variety of different fasts, it's important to establish a reason to go without food, as well as be prepared for the body's possible responses.
Registered dietician Lisa Andrews of Cincinnati's Sound Bites Nutrition believes the practice yields some red flags, so fasting is an exercise that requires some prerequisite homework.
1. How does fasting safely help you lose weight?
Andrews has seen fasting gain pulsing popularity for weight loss programs over the past few years.
"Fasting may improve insulin resistance , which may help with weight loss," Andrews said. "Fasting through simple starvation results initially in loss of glycogen (carbohydrate in storage) and water. The pancreas secretes a hormone called glucagon, which signals the liver to release glycogen in a process called glycogenolysis."
Within the first 24 hours of fasting, glycogen is depleted. However, there are some cases where this loss comes with a warning.
Anyone working to increase their fitness level, gain muscle mass or have a history of eating disorders should avoid fasting.
"Muscle tissue is also lost because the body uses protein for fuel in the absence of carbohydrate," Andrews said.
Fasting should never last for a prolonged period of time, as anorexia nervosa becomes a risk. When deprived of food for more than 24 hours, the body uses fat for calories in place of food to preserve muscle tissue. During this process, fat and protein are lost.
2. How often is too often to fast?
Frequency of fasting should be carefully considered to maintain proper health for the long haul. Fasting is practiced regularly in some religions, in which the body has developed familiarity with food abstinence. The body can become used to fasting through a consistent schedule that lasts more than five years, according to Andrews.
When your body becomes accustomed to a fasting routine, she says a once per month regimen appears safe.
On the other hand, some individuals should never fast, as their health could be jeopardized by lack of food.
"Fasting is not advised in persons that are pregnant, breast-feeding, elderly, children, chronically ill persons or those with diabetes," Andrews said.
3. What if I get hungry during a day of fasting?
Each hour of a day of fasting can seem longer and longer when you go without eating. Your hunger could lead to a feeling of weakness before you hit your "I gotta eat" breaking point.
Is there a food you can eat during a fast that won't count against your practice? Cleansing specialists suggest that a small serving of white rice or a few bites of organic berries are okay during a fast, but Andrews said research begs to differ.
"Most research suggests you should try to continue the fast for any health benefit," she said. "In a recent small study in healthy men in Utah, researchers note that fasting for less than 20 hours at a time will not yield many health benefits."
A fasting period can involve feelings of lightheadedness or dizziness because your body isn't getting the food it normally takes in. If those feelings begin, try drinking more water to make sure you're well hydrated. Be careful when doing so, but try to refrain from eating for the most rewarding fast.
"Consuming food or juice would stimulate insulin secretion, and in the absence of other calories, your body would use protein and some fat for energy," Andres said.
4. Can fasting prevent cancer?
Yes, 24 hours without food can help keep cancer away. One theory, according to Andrews, suggests that reducing your food consumption for one day reduces oxidation and metabolism of food.
"End products of metabolism may produce free radicals (unstable molecules that do cellular damage), which can lead to cancer," Andrews said. "Glucose (from carbohydrates) feeds all cells, including cancer cells. By reducing food intake, cancer cells are not 'fed.'"
Plus, high levels of IGF-1 (insulin like growth factor), glucose in the blood and being heavy (overweight or obese) all increase the risk for cancer, she noted.
Cancer patients who participated in a recent study fasted for three days found that their immune system received some benefits, like increased protection from illness.
"Fasting lowers white blood cell counts and triggers stem cell-based regeneration of new immune system cells," Andrews said.
She cautions that fasting might not be ideal for all cancer patients, as eliminating food intake likely will worsen malnutrition.
5. My body was designed to eat, why should I starve myself?
Feeling reluctant to fast makes sense. Eating is a natural, repeated process we do each day, so a ritual that counters that could seem scary.
Fear not - fasting could help you live longer.
"A group of scientists known as the Cronies (Calorie Restricting Society ) have done numerous studies that find that even reducing calorie intake by 25 percent of estimated needs may increase your lifespan," Andrews
If you start fasting, be mindful of your appetite during the next day. You might feel hungrier, but it's important to maintain healthy, controlled eating habits to fully benefit from a fast.
As Andrews sees it, the following day can be mistakenly see as an opportunity to “make up” for what you didn’t eat.
"There is concern for an increased risk for eating disorders if fasting for weight reduction is taken too far," she said.
Stay tuned into your body when taking on a fast. Listen to what it tells you, be mindful of how you feel and remember to play it safe when it comes to food limitations.