What Is Dry Fasting? What Health Experts Need You to Know
What is dry fasting?
Dry fasting—skipping fluids for a period of time for weight loss or potential health benefits—is a type of intermittent fasting. But is this type of fasting actually good for you? Most dietitians are quick to caution against dry fasting, suggesting that the risks may outweigh any benefits.
Dry fasting calls for not drinking any water or other fluids. Instead, you get your water from food sources such as fruits and vegetables that are high in water content, including cantaloupe, strawberries, watermelon, lettuce, cabbage, celery, and spinach. In its most extreme forms, dry fasting restricts both food and liquid for the fasting period.
Dry fasting is modeled after religious fasts. During the month of Ramadan, Muslims abstain from food and drink from dawn to dusk for 30 days to remind themselves of the less fortunate and encourage gratitude. The Jewish tradition of Yom Kippur is a dry fast from sundown the day before Yom Kippur to one hour after sunset the following day.
How long do dry fasts last?
When undertaken for weight loss or other health benefits, a dry fast can last for varying lengths of time. It can be coupled with other intermittent fasting methods like alternate day fasting, time-restricted feeding, or other types of modified fasts. In addition to avoiding food, you avoid water during your fasting windows or days. In contrast to dry fasts, most other fasts allow you to consume all of the water you want.
“Fasting has been done for millennia for health and spiritual reasons and is built into a lot of cultures,” says Robin Foroutan, RD, integrative medicine dietitian at Morrison Center in New York City and spokesperson for the Academy of Nutrition and Dietetics. “Still, it can be hard to draw conclusions based on data. The limited data we have on dry fasting comes from studies done of religious fasts.”
And as Foroutan points out, “Ramadan fasting is not a continuous fast. It is limited to one month and is done by healthy adults.”
In the context of health and weight loss, dry fasting can offer several benefits, according to limited science and several experts. This type of fasting can also come with certain risks.
Certain people should not participate in any type of fast. This includes women who are pregnant or breastfeeding, or women younger than 25.
Also, avoid fasts if you take insulin or other medications to control diabetes or any medication that must be taken with food, have a seizure disorder, or are at risk for eating disorders or disordered eating, says Dana Greene, RD, a registered dietitian in Boston. You should also avoid fasts if you work with heavy machinery.
Here’s what experts want you to know about the practice.
Dry fasting benefits
Some research suggests that intermittent dry fasting results in short-term weight loss. In a study in the Journal of Human Nutrition and Dietetics, people who fasted during Ramadan experienced weight loss after a one-month dry fast. A study in the Journal of Religion and Health found that dry fasting also produced reductions in LDL (low-density lipoprotein) or “bad” cholesterol levels and fasting blood glucose levels. Note, LDL improvement was seen particularly in male subjects. This suggests the body is properly using the hormone insulin to lower blood sugar levels and stave off type 2 diabetes.
Still, this is just water weight and it will come back the moment you start to eat or drink regularly again, says Greene. “Dry fasting may seem like a good idea to lose weight, but it can cause you to become dehydrated and feel nauseated,” she says.
Improved immune function
Limited calorie intake may improve your immune response.
“Some types of fasting reset your immune system by removing dead and damaged cells and regenerating new ones,” Foroutan says. This cellular anti-aging process is known as autophagy.
Healthier looking skin
Some research suggests that fasting slows down age-related changes, including skin aging. However, Greene cautions that the risks of not getting enough water are much greater than any perceived benefit, including healthier-looking skin. “The best thing you can do for your body is to get enough water,” she says.
Inflammation is linked to a growing number of diseases and conditions, and dry fasting may lower markers of this process. These positive changes peaked during the third week of dry fasting, according to a study in Nutrition Research.
Dry fasting risks
Not getting enough water is a setup for becoming dehydrated, says Lisa Richards, creator of The Candida Diet and a certified nutritionist in Wilmington, Delaware. About 60 to 70 percent of your body weight is made up of water, and every part of your body needs that water to function properly. “Dehydration is a serious risk when it comes to dry fasting,” she says. “Excessive hunger, fatigue, and irritability are common side effects among those actively dry fasting.”
To stay hydrated, women need about 11.5 cups of water a day and men need about 15.5 cups. These estimates include fluids from foods and drinks. According to the Academy of Nutrition and Dietetics, most individuals get about 20 percent of their water from food.
Some fruits and veggies contain 90 to 100 percent water content, including cantaloupe, strawberries and watermelon, as well as lettuce, cabbage, celery, spinach, and cooked squash.
Those with a 70 to 89 percent water content include bananas, grapes, oranges, pears, pineapples, carrots, cooked broccoli, and avocados.
A study, published in 2019 in the International Journal of Environmental Research and Public Health, showed that people who did not drink water for 36 hours experienced fatigue, short-term memory loss, reduced attention spans, and delayed reaction times. This study was designed to look at the effects of dehydration on mood, not dry fasting.
Dry fasting may increase your chances of developing painful kidney stones. They form more easily when there isn’t enough water to prevent stone-forming crystals from sticking together.
Urinary tract infections
The dehydration that could be associated with dry fasting may also increase your chances of a urinary tract infection. Water also helps you make more urine to flush out urinary tract infection-causing germs.
Dry fasting versus water fasting
Unlike dry fasting, water fasting is defined as the complete abstinence of any food or other liquids except for water. Generally, these fasts last 24 to 72 hours. “Both water fasts and dry fasts are extremely risky,” Greene says. What’s more, the weight loss they produce won’t last. Make sure to talk to your doctor before starting either of these fasts.
The last word
Dry fasting is the restriction of food and drink. Aside from religious purposes, the intent of this fast is to promote weight loss and good health. However, the science on this type of fast is limited. Dry fasting can lead to dangerous risks, including dehydration and other health conditions, like kidney stones.
- Robin Foroutan, RD, integrative medicine dietitian, Morrison Center, New York City and spokesperson for the Academy of Nutrition and Dietetics.
- Journal of Human Nutrition and Dietetics: "Effect of fasting in Ramadan on body composition and nutritional intake: a prospective study"
- Journal of Religion and Health: "Does Ramadan fasting alter body weight and blood lipids and fasting blood glucose in a healthy population? A meta-analysis"
- Dana Greene, RD, dietitian, Boston
- Nutrition Research: "Intermittent fasting during Ramadan attenuates proinflammatory cytokines and immune cells in healthy subjects"
- Lisa Richards, a certified nutritionist, Wilmington, Delaware and creator, The Candida Diet
- Academy of Nutrition and Dietetics: "How Much Water Do You Need"
- International Journal of Environmental Research and Public Health: "Effects of Dehydration and Rehydration on Cognitive Performance and Mood among Male College Students in Cangzhou, China: A Self-Controlled Trial"
- National Kidney Foundation: "Can Dehydration Affect Your Kidneys?"
- National Institutes of Health: "To Fast or Not to Fast: Does When You Eat Matter?"