Fasting has long played a role in diverse religious traditions. Catholics fast before receiving communion and abstain from meat on Fridays during Lent, Jews fast during Yom Kippur, and Muslims fast intermittently during the month of Ramadan.

The faithful aren’t the only ones who fast, though. Fasting is an increasingly popular way to lose weight, gain clarity, and “cleanse” the body of perceived toxins. However, fasting can be dangerous, particularly when it means depriving the body of vital nutrients over time. The right fasting strategy doesn’t have to be unhealthy. Here’s how to reap the spiritual, physical, and personal benefits of fasting without endangering your health.

Know Whether It’s Safe for You to Fast

Some groups should avoid fasting. Even religious traditions that view fasting as fundamental to faith will typically excuse people from fasting if doing so would endanger their health. So if you’re trying fasting for the first time, talk to your doctor. The following groups should not fast:

  • Pregnant women: Not eating can exacerbate morning sickness and dizziness. More importantly, it can endanger the developing baby. Nutritional deficits are a risk factor for a range of negative pregnancy outcomes, including neural tube defects, miscarriage, premature labor, and stillbirth.
  • Breastfeeding women: Breastfeeding burns several hundred additional calories, which means that breastfeeding women are more vulnerable to malnutrition and excessive weight loss. Malnutrition can affect milk supply, as well as the nutritional content of breast milk.
  • People with a history of eating disorders: If you have or previously had an eating disorder, extreme diets can trigger a relapse. Continue eating a regular, balanced diet. If you want to fast for religious reasons, consider giving up a much-beloved food instead.
  • People with certain chronic illnesses: Some chronic illnesses require regular, scheduled eating. People with type 1 or type 2 diabetes should usually avoid fasting, particularly if they take medication that lowers blood glucose. Those with kidney or liver disease, anemia, or medical conditions that require special diets should also avoid fasting.
  • Children: Children should not fast, even if they are overweight or choose to fast because of their spiritual commitments. Fasting can disrupt children’s physical and cognitive growth and make it difficult for them to concentrate at school, and in children with body image issues, it may lead to eating disorders.

Remain Hydrated

You can live a lot longer without food than you can without water, so continue drinking water even if you’re temporarily not eating. Adequate water intake can even make fasting a little easier since you won’t feel weak from dehydration.

Consider a Partial Fast

A partial fast offers the same benefits of fasting, but it decreases the risk of malnutrition. The basic idea is to narrow the window during which you eat. You might eat only at night, abstain from food in the hours leading up to a big event, or limit yourself to just one or two meals. Another option is to eliminate specific foods. This strategy can work well for people who want to cut calories, as well as those who want to cultivate a more spiritual mindset by making a significant sacrifice. Some options include:

Another option is to try an alternating day approach. With this style of fasting, you fast one day, limiting yourself to just a few hundred calories. On the following day, you eat normally. The theory is that you’ll eat fewer calories than you would otherwise, but the day of regular eating will prevent your body from going into “starvation mode,” potentially helping you lose weight.

Watch Your Calories Before and After the Fast

Before you fast, make sure you continue eating a balanced, varied diet to reduce the risk of malnutrition. After a fast, it may be tempting to gorge yourself on all the foods you’ve missed. If you’re trying to lose weight by fasting, this strategy can backfire. Even if weight loss is not your goal, binging can undermine your health. Instead, return to a varied, balanced diet.

Get Clear About Your Goals

If you plan to fast to cultivate a more spiritual mindset and avoid the distractions of the material world, think about how best to achieve this goal. The right timing is important. Stress, social outings, and exhaustion can make it more difficult to fast, so plan accordingly.  

If you hope to lose weight, then know that research on the role of fasting for weight loss is mixed. One study found that both fasting and traditional calorie reduction produced similar weight loss results. Other research suggests that people who fast tend to regain the weight they’ve lost after the fast. If you hope to lose weight and keep it off, you’ll need to watch your calorie intake even after you've finished fasting.

Weigh the Benefits of Juice Fasts

Juice fasts promise to reduce the calories you consume while providing enough nutrition and hydration to keep your body working well. If you can’t stomach the thought of giving up food for a day or two, a juice fast may be an easier and less stressful bet. Beware of juice fasts that encourage long-term fasting, or that promise to cleanse or detox the liver. The liver and kidneys are the body’s own detox system, and there’s little evidence that drinking juice will “cleanse” them.

Remember that fasting can never be a long-term weight loss strategy. Calories are not evil. They are fuel for the body and brain. Extended periods without eating can cause lasting damage. Body weight is just one way to measure health. No matter how much weight you lose, you won’t be healthy if you’re malnourished.