Water Fasting Benefits, Dangers, & My Personal Experience

Water Fasting and why I will do it again

I mentioned in a few recent podcast episodes and Instagram posts that I’ve been experimenting with water fasting, and immediately received a lot of questions about the specifics. I’ll answer all those questions here.

The short answer is that overall, water fasting was an amazing experience and I’ll definitely do it again. But before we go any further, I must emphasize that this is MY experience after a lot of research and after talking to several doctors and practitioners. I’m not suggesting anyone else try fasting, at least without the same due diligence. While fasting is generally considered safe for short amounts of time, not everyone can or should try it.

This is what worked for me…

What is Water Fasting?

As the name suggests, it is fasting on water. And only water. And nothing but water.

Herbal teas, black coffee, calorie free drinks, and supplements are not part of water fasting. Just water.

If it sounds tough, I can say that from my experience water fasting is much easier than other types of fasting (bone broth, juicing, etc.) and the results are much more profound. This type of fasting is also called block fasting or long-term fasting.

Fasting can vary in duration from 24-72 hours, which is considered safe for most people. Or the fast can extend to five days, seven days, or even 40-days. The longest I’ve personally fasted is 7 days.

Why I Decided to Fast (on Water Only)

Historically, every major religion recommends or requires fasting in some way. Throughout history, many people have fasted by default when access to food was limited or during travel when food was unavailable.

In modern times, the idea of voluntarily going without eating seems absurd to some, though to many people throughout history, the idea of eating 4-6 times a day would seem equally absurd. In fact, the modern idea of “six small meals a day” would have seemed crazy to even the wealthiest in the world until recently, as it simply wasn’t an option.

Even more shocking? Researchers estimate that Americans actually don’t even eat just 4-6 times a day. The actual number is closer to 17-18 times a day. Not you? Consider this… from a biochemical perspective, anytime we put something caloric in our mouths, there is a digestive event. Every hand full of nuts, every sip of smoothie between meals or coffee with cream. The body sees all of those as digestive events.

In short, these days we eat more, move much less, get less sunlight and much more artificial light exposure. The odds are not in our favor.

I decided to fast as much for the mental benefits as the physical, though there is research to back the physical benefits as well.

The Benefits of Water Fasting

Confession: I read medical journals for fun. I’m weird like that. (Want to read some of the studies I found? They are all in the sources below.)

I started finding studies that show that short term fasting can:

  • Create autophagy in the body
  • Lower age-induced inflammation in the body
  • Reduce oxidative damage
  • Lower NF-kB activation
  • Boost the immune system

Why are those things a big deal?

Because inflammation and oxidative damage correlate to lifespan. Increased inflammation and oxidative damage correlates to early death, while reduced levels equate to longer life. People who live to be 100+ years old share the common factor of low levels of inflammation in the body.

What is Autophagy?

Glad you asked.

It is a self-eating process (the word literally means “self-eating”). Essentially, during autophagy, the body recycles old parts to create new parts. Or as a recent study explains it a little more scientifically:

Autophagy also plays a housekeeping role in removing misfolded or aggregated proteins, clearing damaged organelles, such as mitochondria, endoplasmic reticulum and peroxisomes, as well as eliminating intracellular pathogens. Thus, autophagy is generally thought of as a survival mechanism.

Research shows that autophagy is a key part of the body’s ability to detoxify and regenerate itself. Fasting and high intensity exercise both stimulate autophagy and can lead to positive results for this reason. Even intermittent fasting can have benefits, though the biggest results seem to come from longer term fasting.

Studies have found that autophagy can lead to a decreased risk of cancer, heart disease and alzheimers. Other studies found that autophagy can increase longevity and reduce all cause mortality. Recycling = good for cardboard and good for our cells too!

While religions around the world have long revered fasting for its mental and spiritual reset, it turns out it has a biological reset component as well through autophagy.

Lower Inflammation and Oxidative Damage

Two other major reasons I decided to give fasting a try.

Studies show that fasting reduces pro-inflammatory cytokines and inflammation in the body. Specifically, researchers at Yale School of Medicine found that a compound called ?-hydroxybutyrate (BHB) inhibits NLRP3.

NLRP3 is part of a set of proteins called the inflammasome which drives the inflammatory response in several disorders including autoimmune diseases (important for me with Hashimotos), as well as type 2 diabetes, Alzheimer’s disease, heart disease, and other auto-inflammatory disorders.

The researchers found that BHB is produced by:

  • Fasting (most effective)
  • High intensity exercise
  • Caloric restriction
  • A ketogenic diet

Reduce Cancer & Heart Disease Risk

Emerging research also shows a link between fasting and reduced cancer risk. This is likely due to the two factors listed above: increased autophagy and reduced oxidative damage/inflammation.

But research also showed that water fasting may slow or halt the growth of tumors, as well as improve the effects of chemotherapy and reduce the side effects, making it potentially beneficial when combined with conventional cancer treatments.

Yet another study found that water fasting can help protect the heart against damage from free radicals.

One doctor I spoke to claimed that 1-2 five day water fasts a year could reduce cancer risk by more than 90%! Even if the results aren’t that dramatic, I decided it was worth a try!

Boost the Immune System

A 2014 study found that water fasting for just three days could regenerate the immune system. The researchers found that fasting “flips a regenerative switch” and prompts stem cells to regenerate new white  blood cells.

“It gives the ‘OK’ for stem cells to go ahead and begin proliferating and rebuild the entire system,” according to Dr. Valter Longo, Professor of Gerontology and the Biological Sciences at the University of California and author of The Longevity Diet.

This research makes fasting a promising practice for those with immune problems, those undergoing chemo, and for all of us as we age, since immune function declines with age.

Improve Brain Function

When fasting, the body switches from burning glucose to burning fat. Instead of glucose, the brain uses ketones for fuel. Ketones are largely considered more efficient fuel for the brain. For this reason, fasting is associated with increased mental clarity, focus and concentration.

My Experience Fasting on Water Only

I researched quite a bit and talked to several experts before jumping in to a water-only fast. Like I said, I’m not suggesting this for anyone else, just sharing my personal experience. Anyone considering water fasting should do additional research and talk to or be overseen by a qualified professional.

My husband decided to fast with me so we picked a week that was free of travel and any major scheduled activities. This turned out to be a good thing because fair warning.. the first few days of fasting are not fun. At all. But they also aren’t as bad as you might think.

The few days before the fast, we focused on eating a lot more green veggies, drinking enough water, and taking supplements (they aren’t allowed on a water fast either). We also made sure our electrolytes were up with homemade electrolyte drinks and adding salt to our food.

Testing on the Water Fast

My experiments with fasting were for research as well as the health benefits. To be able to evaluate the effects on my body, I did several types of testing before and during the fast, including:

  1. Full CBC and Thyroid Blood Panel- I ordered without a doctor through Life Extension (click on “lab testing”). I did this before and after the fast to measure results.
  2. Ketone Testing & Blood Glucose Testing– We used a Keto Mojo meter for both of these. According to the practitioners I talked to, you want a 1:1 or greater ratio of ketones:glucose in mmol/L during fasting to show autophagy. If you have a regular glucose meter that measures in mg/dl, you can divide that number by 18 to get the mmol/L. For instance, my normal fasting blood glucose of 71 divided by 18 is 3.94 mmol/L.
  3. Breath Acetone Testing– This test measures the amount of ketones actually being used and can predict fat burned. The blood ketone measurement above determines ketones in the blood, and this one measures how it is being used. We used the Levl device for this measurement. Of all the tests, I would consider this one the least important.
  4. Gut Testing– I’m still awaiting my follow up results, but I tested my gut using Viome before and after fasting to see if there were any dramatic shifts in gut health. I will update this when my results come in.

What Kind of Water on the Fast?

Since water is the only thing we consumed during the fast, it was important to make sure we had high quality water. We have a whole house filter and a 14-stage under the sink filter, so we were fine with drinking our tap water. Some people prefer to use distilled water while fasting.

Electrolyte depletion is one of the bigger risks of fasting (see the others below) so we added some high quality Himalayan salt to a couple of glasses of our water each day. This is supposed to help with the headaches and tiredness.

The amount of water is also important during a fast. Drinking too much water can cause problems, as can not drinking enough. Sources vary on the exact amount but it ranges between 2-4 quarts a day. I just drank when thirsty and added a pinch of salt to a couple glasses a day.

Avoiding Toothpaste & Lotion During the Fast

Sources disagree on what products, if any, should be used while fasting. Some claim that any lotion, toothpaste or deodorant will create a metabolic change and will break the fast. They recommend brushing with a plain wet toothbrush and scraping the tongue and skipping the deodorant. Others say that normal external products are fine.

Since I make almost all of my beauty and personal care products, I felt ok using them. I used a natural toothpaste and used magnesium oil for deodorant, since epsom salt baths are considered ok. I also used soap daily and didn’t notice any negative effects from this.

My Day-by-Day Water Fast Experience

I didn’t really know what to expect with fasting on water alone, other than the autophagy and hopefully increased stem cell activity. This is what I experienced day by day during the fast:

Day 1

For our first fast, we weren’t sure what to expect but we scheduled an easy first day. This was a good call. The first half of the day was just like any normal day, minus breakfast and lunch. By dinner, our bodies started to notice they hadn’t eaten all day and the hunger hit. Then the tiredness.

Overall, it wasn’t a terrible day and we just took it easy. We went to bed around 9 PM that night and got about 10 hours of sleep.

Day 2-3

These middle days were rough. We were still hungry (obviously) but also had fatigue and even slight body aches. I also got cold, and this is likely due to the changes in T3 that naturally happen during fasting. The body does this to protect muscle and it is a good thing, but I spent a lot of time on the couch with blankets these two days.

I wouldn’t go so far as to say these days were as bad as the flu (though it’s been a long time since I’ve had it), but they were rough. Now, these are days we plan to rest and sleep.

Days 4+

I loved days 4-7 of fasting! Energy came back with a vengeance and hunger disappeared. I was easily at 2-3x my normal productivity. Many sources claim that this is due to having more time without the need to cook food a few times a day. In my case, this wasn’t true since I still had to cook 3 times a day for our kids.

Since we were measuring blood ketones, I know that our ketones were above 4.0 on these days and our adjusted glucose was below it. This means we were in autophagy. The Levl device also confirmed we were effectively using ketones. Ketones are considered cleaner and more effective fuel for the brain by some experts, and I’m guessing the mental clarity came from the increased ketones.

The one complaint I had during this time was some itchy skin. From my research, this can be a common reaction to fasting and to weight loss, and an epsom salt bath alleviated it.

Breaking a Water Fast Carefully

Surprisingly, if not done correctly, the most dangerous part of fasting can be the return to normal eating. The longer the fast, the more important the post-fast refeeding period is. In extreme cases after long fasts, the body can encounter something called refeeding syndrome when fluids, insulin, and electrolytes get out of balance. In really extreme cases, this can be fatal, so breaking the fast correctly is VERY important!

The sources I read recommend starting with broth, soft cooked veggies, some gentle fruits and fermented vegetables. Meats, fish, dairy and raw vegetables are all a little harsh for breaking a fast, so we waited until day 3 post-fast for these. Additionally, we waited 4-5 days before adding in caffeine or alcohol in very small amounts. Our refeed looked like this by day:

  1. Broth, soft cooked veggies in olive oil, avocado, berries and sauerkraut (It all tasted amazing!). We broke the fast at night and kept it to 500 calories for the day to let our digestive systems start working slowly.
  2. Added in sweet potato and more volume of food.
  3. Added slow cooked meats and fish. Also added in supplements.

My Water Fasting Results

After the middle of day 3 we felt really good while fasting and I’d do it again just for the mental clarity. I was also testing my blood levels before and after fasting to make sure it didn’t negatively affect my thyroid. Not only was it not harmful for my thyroid, but my levels actually improved! The biggest changes I noticed from fasting are:

  • Weight loss– I lost over 15 pounds during a one-week fast, of which 12 pounds stayed off. The other three pounds were likely from water and food in the digestive system.
  • Fasting blood glucose– My fasting blood glucose was always pretty good- in the mid 80s most days. While fasting, it got as low as the 50s but has normalized and is consistently 71-73 every morning, even now that the fast has ended.
  • Thyroid levels– Thyroid antibodies were already low but got even lower after fasting. All other thyroid hormones stayed the same or improved.
  • Cholesterol– My cholesterol numbers and ratios have always been good, but improved post-fasting. For a short time, they were slightly elevated, which is normal after fasting, weight loss, or being in ketosis. Then, they normalized and returned to slightly better levels.
  • Faster Adaptation to Ketosis– I’m experimenting with cycling ketosis and using it sometimes for mental clarity. Since fasting, I can get into ketosis with dietary changes alone much more quickly. By day one of the fast, I had achieved ketosis and saw levels get as high as 5.8 during the fast. Since then, I can get into ketosis in one day by just restricting carbohydrates.

Who Should Not Water Fast

In short, no one should fast just because I did, and everyone should thoroughly research and talk to a medical professional before trying any water fasting. Common sense and research agree that fasting is also not a good idea for:

Pregnant and Breastfeeding Moms

The time spent growing and nourishing a baby is a special (and exhausting) time, and not a time to add fasting into the mix. Fasting during these times can lead to nutrient deficiencies and harmful substances being released into breastmilk.


This should go without saying, but growing children should never do an extended fast. In our house, our kids sometimes choose to “fast” for one meal rather than eat a food they don’t love or if they aren’t hungry. This encourages them to listen to their bodies and only eat when hungry. It is not the same as an extended fast and growing children should never restrict calories for extended periods of time. That said, kids do seem intuitive and often don’t want to eat much when sick, and as long as they consume enough fluids, this is generally considered ok.

Those With Medical Conditions

Anyone with a medical condition should talk to a doctor before attempting any major dietary change such as fasting. Those with gout, kidney disorders, eating disorders, or diabetes should not fast unless under the direct recommendation of a medical professional.

Other Ways to Fast

Water fasting is just one way to get the benefits of fasting. In my experience it produces the most rapid results, but similar effects can occur from:

Intermittent Fasting

Eating all meals in a restricted time window each day can have similar beneficial effects over time. Also called Time Restricted Eating (TRE), this type of fasting requires eating in a 6, 8, 10, or 12 hour window each day and avoiding calories outside this window. This post explains how.

The 5:2 Fast

This method involves eating normally five days a week and fasting entirely or limiting food to 500 calories two days a week. Many people seem to have good results with this method and find it easier to stick to.

Fasting Mimicking Diet

Recommended by Dr. Valter Longo, this method mimics fasting while still including food (as the name suggests). In his studies, this diet produces similar outcomes to water fasting and may be preferable for those with blood sugar issues or those who can’t fully fast.

Fasting mimicking diets are often done for 5-days a month. During these days, food is restricted to under 1,000 calories and to certain macronutrient ratios.

The Bottom Line of Water Fasting

I had a positive experience with water fasting… except for the first couple of days. I’d do it again for the mental clarity and physical benefits and I plan to work it into my schedule every few months. I also think, after researching about fasting, that diet variation is beneficial.

Additional Learning:


  1. Alirezaei, Mehrdad et al. “Short-Term Fasting Induces Profound Neuronal Autophagy.” Autophagy 6.6 (2010): 702–710. PMC. Web. 2 Mar. 2018.
  2. Castello L, Froio T, Maina M, et al. Alternate-day fasting protects the rat heart against age-induced inflammation and fibrosis by inhibiting oxidative damage and NF-kB activation. Free Radic Biol Med. 2010;48(1):47-54.
  3. Glick, Danielle, Sandra Barth, and Kay F. Macleod. “Autophagy: Cellular and Molecular Mechanisms.” The Journal of pathology 221.1 (2010): 3–12. PMC. Web. 2 Mar. 2018.
  4. Mah LY, Ryan KM. Autophagy and Cancer. Cold Spring Harbor Perspectives in Biology. 2012;4(1):a008821. doi:10.1101/cshperspect.a008821.
  5. Zare-shahabadi, Ameneh et al. “Autophagy in Alzheimer’s Disease.” Reviews in the neurosciences 26.4 (2015): 385–395. PMC. Web. 2 Mar. 2018.
  6. Shirakabe A, Ikeda Y, Sciarretta S, Zablocki DK, Sadoshima J. Aging and Autophagy in the Heart. Circ Res. 2016;118(10):1563-76.
    Brandhorst, Sebastian et al. “A Periodic Diet That Mimics Fasting Promotes Multi-System Regeneration, Enhanced Cognitive Performance and Healthspan.” Cell metabolism 22.1 (2015): 86–99. PMC. Web. 2 Mar. 2018.
  7. Levine, Beth, and Guido Kroemer. “Autophagy in the Pathogenesis of Disease.” Cell 132.1 (2008): 27–42. PMC. Web. 2 Mar. 2018.
  8. Lee, Changhan et al. “Fasting Cycles Retard Growth of Tumors and Sensitize a Range of Cancer Cell Types to Chemotherapy.” Science translational medicine 4.124 (2012): 124ra27. PMC. Web. 2 Mar. 2018.

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