Is Dry Fasting Safe?

Medically Reviewed by Kathleen M. Zelman, RD, LD, MPH on May 02, 2023
3 min read

You've probably heard about the benefits of intermittent fasting, a diet plan that alternates between abstaining from food and eating on a regular schedule. There is evidence that it can help you manage your weight and prevent or reverse some diseases.

Dry fasting can be done with any intermittent fasting method by not drinking or taking in any fluids during the fasting period. Some of the popular fasting schedules include:

Daily time-restricted fast. Eat normally but within an 8-hour window, such as between 10:00 a.m. and 6:00 p.m.

5:2 fasting. Eat normally 5 days per week and fast for 2 days per week. 

Alternate-day fasting. Alternate between eating normally one day, then fasting completely or eating a small meal of under 500 calories the next day. 

Studies have shown a range of benefits from intermittent fasting, including a healthier body and a sharper mind.

There are some proponents of dry fasting, which is abstaining from all food and fluid for a set period of time, who claim it has as many or more benefits as intermittent fasting. However, there is not enough research on the benefits of dry fasting, and many doctors consider it a dangerous practice.

Talk to your doctor before starting a dry fast.

Some of the purported benefits of dry fasting include:

Weight loss. There is evidence that dry fasting causes weight loss. Ramadan is a holy month during which Muslims abstain from all food and drink from sunrise to sunset every day. A study of 240 people who fasted for at least 20 days during Ramadan found that after Ramadan, body weight and body mass index (BMI) decrease in everyone.

Reduced inflammation. Another study of people who fasted during Ramadan showed positive effects on the inflammatory status of the body and on some risk factors for heart disease. 

Chronic inflammation has been associated with heart disease, arthritis, cancer, diabetes, Crohn's disease, and ulcerative colitis.

Delayed aging. Proponents of dry fasting claim that it slows down the aging process. Animal studies have shown mixed results on the effects of fasting on the aging process. Human studies have mostly been short-term and haven't provided enough evidence that it is safe and effective long-term.

Most studies on the benefits of dry fasting have been done on people participating in Ramadan. Ramadan fasting is only done by healthy people and only for one month. 

More research is needed to know if it is safe long-term. Most studies of the effects of intermittent fasting have been done on overweight, middle-aged adults. More research is needed to determine if it is safe for people who are older or younger or people at a healthy weight.

Like intermittent fasting, the side effects of dry fasting can include:

Additionally, since dry fasting can cause dehydration, you may also experience:

  • Thirst
  • Dizziness or lightheadedness
  • Dry mouth, lips, and eyes
  • Dark, strong-smelling urine
  • Urinating less often and a smaller amount

The biggest risk of dry fasting is dehydration. The complications of dehydration can include:

Seizures. When your electrolytes, such as sodium and potassium are out of balance, your body can have trouble sending electrical signals from cell to cell. This can lead to involuntary muscle contractions and a loss of consciousness.

Brain swelling. When you are getting fluids again after being dehydrated, your body sometimes tries to pull too much water back into your cells. Some cells can swell and rupture during this process. If this happens to your brain cells, it can be especially serious.

Heat injury. If you dry fast during strenuous exercise or when you’re very hot, you can develop a heat injury. This can be mild, such as with heat cramps, or severe, such as with heat exhaustion or heat stroke. Heat stroke can be potentially life-threatening.

Kidney failure. If your kidneys are no longer able to remove excess fluids and waste from your body, it can lead to kidney failure, which can be life-threatening.

Low blood volume shock. This life-threatening condition called hypovolemic shock occurs when low blood volume in your body causes a drop in your blood pressure and a drop in the amount of oxygen in your body.

Coma and death. If not treated quickly, severe dehydration can be life-threatening.