One Form of Fasting May Bring Benefits More Quickly Than Others

Dry fasting, meaning abstaining from water in addition to food, may offer more rapid healing, but necessitates a slower, more deliberate approach.

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Digestion is an important biological function with cascading effects on the entire body. Ceasing digestion can be just as vital for health because it offers the body a state of rest in which it can repair itself.

Research continues to document the benefits of fasting, especially for longer periods. However, the practice can be difficult even for those who can tolerate it.

“The problem with prolonged fasting is the prolonged part,” chiropractor and health influencer Eric Berg told an audience at a recent Hack Your Health conference in Austin, Texas. “It’s not easy. I have a solution. It’s something that can get better results in faster time.”

Called “dry fasting,” it’s a form of fasting that removes all forms of hydration—tea, coffee, supplements, and even water—as well as food. Animal and other studies hint that dry fasting for one day may offer the same benefits as three days of fasting from food while still drinking water—known as “water fasting.”

More recently, researchers have conducted human studies noting benefits that are protective against heart disease, cancer, and inflammation.

Dr. Berg explained, however, that the practice of dry fasting requires a gradual approach, knowledge about how to fuel the body correctly when breaking the fast, a mindset shift regarding dehydration, and possibly a conversion with your doctor.

“It’s pretty easy to do, especially if you do it on a gradient slowly. You can do it for 12 hours, between sunsets and sunrises,” he said. “It is not that hard to do a dry fast for 12 hours, and it’s not dangerous.”

Protective Benefits

Many religions practice fasting, and Muslims fast from all food and water from sunrise to sunset for an entire month during the time of Ramadan. The fasting during Ramadan has allowed researchers to examine the effects of dry fasting.

One study published in 2022 in Metabolic Open found decreased proteins associated with atherosclerosis, heart disease, and cancer promotion and an increase in proteins capable of suppressing cancer and inflammation among those fasting for Ramadan.

Researchers sampled blood before the fasting period of 14 subjects who had metabolic syndrome and compared them to blood samples taken the day fasting ended and one week after the completion of fasting. The testing was done on peripheral blood mononuclear cells—major cells in human immunity—offering a glimpse of cellular-level metabolic pathways.

“After fasting, our participants lost weight, and their blood pressure and insulin resistance improved,” said Dr. Ayse Leyla Mindikoglu, corresponding author of the study and associate professor at Baylor College of Medicine, in a news release. “The findings of this study are important because we were able to confirm the favorable effect of dawn-to-dusk dry fasting at the cellular level.”

The subjects all suffered from metabolic syndrome, a group of conditions that includes obesity, high blood pressure, insulin resistance, and other factors that put them at risk of heart disease, cancer, and Type 2 diabetes.

The news release noted that during the non-fasting times, the participants ate anything they wanted and were not required to exercise or attempt to lose weight. At the end of the month of fasting, apolipoprotein B—a more accurate risk predictor for developing atherosclerotic heart disease than low-density lipoprotein (LDL) cholesterol—had significantly decreased and remained low one week after fasting.

Dr. Mindikoglu said the study also revealed how fasting can help reset circadian rhythm, which is considered a major factor in protecting human health. Disrupted circadian rhythm has been associated with heart disease and Type 2 diabetes.

Previous research on daytime dry fasting published in 2021 in Frontiers in Nutrition has shown that it may advance circadian rhythm slightly—like setting your clock ahead by an hour—but that it readjusts after fasting and was still associated with improvements in fat metabolism.

Speeding up Autophagy

A 2016 rodent study notes that one day of dry fasting offers the same benefits as three days of water fasting based on measurements of autophagy, a process cells undergo to recycle damaged proteins and other substances to improve cell function.

Autophagy can also help the body rid itself of bacteria and viruses, as well as prevent cells from morphing into cancerous cells, according to the National Cancer Institute.

The study examined autophagy‑specific long‑chain protein 3 over four days in three groups of mice—those that drank water but didn’t eat, those that ate but didn’t drink water, and those that had no food or water intake.

All types of fasting activated autophagy in cerebral cells of the studied mice. However, in the mice deprived of both food and water, autophagy increased significantly on the first day, whereas the other groups had a sustained, cumulative effect over three days.

A human study published in March 2024 in Metabolism Open examined the effects of dry fasting on 13 obese subjects and noted that it “appears to be a unique treatment to reduce low-grade chronic systemic inflammation caused by visceral obesity, without compromising the body’s innate and adaptive immune mechanisms.”

Research on dry fasting shows “a fascinating situation where your immune system gets enhanced, your autophagy gets super-enhanced,” Mr. Berg said.

Understanding Dehydration

Mr Berg said there are more than 50 genes that protect the body against dehydration, though the practice of dry fasting hasn’t been immune to critics, many of whom use inaccurate information to warn against it.

He mentioned the following often-cited dehydration misconceptions:

• If you are thirsty, you are already dehydrated.
• Without water, you won’t live beyond three days.
• You need water to flush out toxins.
• You should drink water until your urine is clear.

“There are a lot of fixed ideas in the area of dehydration,” Mr. Berg said. “You typically want to drink when you’re thirsty. Just as we have dehydration, we also have over-hydration.”

The 2016 rodent study showed no loss of water in cells during any of the fasting periods.

Dr. Christopher Labos, health writer and cardiologist/epidemiologist, wrote an article on the topic of water myths for McGill Office for Science and Society and noted a study in the Journal of the American Medical Association showing drinking more water doesn’t offer additional benefits for kidney function.

Precautions for Some

Still, some doctors aren’t likely to issue a broad permission slip for anyone to try prolonged dry fasting—especially those with a medical diagnosis.

A 2023 review article on intermittent dry fasting related to Ramadan noted that while there’s a long list of benefits, certain people experienced aggravation of gut-related disorders.

Specifically, the review noted minimal risk for problems associated with dry fasting and inflammatory bowel disease, though older men with ulcerative colitis appeared to have exacerbation of symptoms.

Also, patients participating in Ramadan fasting with duodenal ulcers had higher risk of hemorrhage. There were mixed results for patients with moderate to severe liver disease who had a higher risk of disease complications and flares while fasting.

However, the review noted the practice can aid in weight loss for obese patients, lower LDL cholesterol and triglyceride levels, optimize circadian rhythms, improve the gut microbiome, modify gut hormone levels, and lower proinflammatory markers like cytokines and blood lipids.

Start Slow

For those who have their doctors’ blessings, the best advice is to begin the practice slowly and gradually, Mr. Berg said. He offered the following tips:

1. Practice intermittent fasting before prolonged fasting. Intermittent fasting is shortening your eating window. For instance, you might eat all your meals in an eight-hour period during the day.
2. Try water fasting before attempting dry fasting.
3. Begin with short periods of dry fasting. For instance, on the first attempt, dry fast through the night. On the second attempt, skip breakfast, including coffee and other hydration. On the third attempt, make the window of eating and drinking a shorter time frame later in the day.
4. You can work up to longer periods of dry fasting for two to three days, and for some, even longer.
5. Do not do high-intensity interval training while fasting. Fasting should be the main stressor on your body.
6. Eventually, you’ll want to alternate between shorter fasts and longer ones.
7. Refrain from caffeine for three days before fasting.
8. Come off the fast as gradually as you go on. That means for longer fasts, ease into hydration with bone broths and juicing. Stay away from fat and salt in the first few days after longer dry fasts.

“Kefir is a really good one to take, usually diluted, throughout this refeeding, because your microbiome has literally been asleep,” Mr. Berg said. Kefir is a fermented milk drink containing millions of probiotics, or good bacteria.

Insulin resistance will make fasting more challenging, he said and will require longer to adjust to fasting. Insulin is a hormone made in the pancreas that helps pull sugar from the blood to use as energy. When the cells stop responding to insulin, the condition is called insulin resistance—a scenario that can cause elevated blood sugar levels and lead to Type 2 diabetes.

“Some people are very good at fasting. When I started doing fasting, I had a hard time doing it. It can take months to get used to it,” Mr. Berg said.