Author: Troy Theodosiou

Water fasting is a type of fast that restricts everything except water. It has become more popular in recent years as a quick way to lose weight.

That said, human studies on water fasting are very limited. Moreover, it comes with many health risks and is not suitable for everyone.

Most water fasts last 24–72 hours. You should not follow a water fast for longer than this without medical supervision.

Here are a few reasons why people try water fasting:

  • religious or spiritual reasons
  • to lose weight
  • for “detoxing”
  • for its health benefits
  • preparing for a medical procedure

When the body does not have access to carbohydrates, which are its preferred source of energy, it will use fats. So, a fast can result in weight loss as the body uses up fats in the body for its energy.

Even if you stick to the recommended 24 to 72 hours, a water fast can still be detrimental to people with certain medical conditions. People who should not try a water fast include those with:

  • Chronic kidney disease—fasting may worsen kidney function7
  • Heartburn or gastroesophageal reflux disorder (GERD)—your stomach may continue to make stomach acid even without food, which can worsen symptoms of heartburn and GERD
  • Diabetes—fasting may increase a person’s risk of diabetic ketoacidosis and hypoglycemia (low blood sugar)
  • Eating disorders—fasting may lead to disordered eating patterns like a binge-restrict cycle

According to the Academy of Nutrition and Dietetics, the best way to lose weight is to take it slowly, combining a healthy diet with exercise. It is also important to try and change some eating habits, such as reducing the number of sugary foods and snacks eaten.

Although there may be some health benefits to water fasting, reducing overall calories is just as effective for weight loss, and is likely to be safer. Alternatives such as intermittent fasting could have more health benefits in terms of reducing the risks for heart disease and diabetes than a long-term water fast for days at a time and may be more sustainable.