I Did A 3-Day Water Fast:
The How, Why + Tips
Thinking of trying a water fast? I recently did a 3-day water fast. Read on to learn the how and why – plus the science behind water fasting. I’m also answering your common fasting questions like “can I have coffee?” and “does fasting produce autophagy?”
Disclaimer – fasting is not for everyone. Talk to your doctor before beginning a fast. Fasting for 7 days or more should be medically supervised. If your only goal is weight loss, I personally believe there are better, more sustainable options.
I have a secret to tell you — I recently did a 3-day water fast.
I know. It sounds a little crazy, extreme, and totally contrary to the fad-free, evidence-based nutrition information that I usually share here, but bear with me for a second and let me explain.
If you’ve read my previous posts on intermittent fasting and time-restricted eating, then you know that the science on various types of caloric restriction is solid.
It’s pretty remarkable actually, caloric restriction can extend lifespan in mice up to 50%. Decades of research have shown that fasting improves some measures of metabolic health in humans and prevents chronic disease in animals.
I’m a big fan of what I call “Common Sense Fasting” – simply putting at least 12 hours between dinner and breakfast. You can learn more about that in my intermittent fasting post.
But water fasting, well that’s a different ballgame.
I’d heard of people going 3 to 30 days without food, and always thought it seemed a little insane. But the thing is, if you look at the science, it’s not that outlandish.
While short-term fasting, 12-18 hours, has been shown to reduce disease risk factors in humans, one of the major purported benefits of fasting is cellular rejuvenation, aka autophagy, which doesn’t occur in mice until about 24 hours of fasting.
You’ve probably heard of “dog years” – they’re shorter than human years – well, mice days are similar. One day of fasting for a mouse is not equivalent to one day of fasting for a human. So, if it takes 24 hours to increase autophagy in a mouse, it’s going to take even longer in humans.
So basically, typical intermittent fasting protocols (while beneficial in other ways) are likely not long enough to reap cellular regenerative benefits.
Unfortunately, the research on “prolonged fasting” in humans is pretty sparse. But many fasting experts, including my former professor Dr. Valter Longo, recommend it 1-2 times a year for overall health.
I decided that a yearly prolonged fast was something I wanted to include in my disease-prevention toolbox. Three years ago, I did a 5-day Fasting Mimicking Dietary Protocol. Then I spent almost two years pregnant and breastfeeding, so of course, no fasting then.
This time, I wanted something shorter and a three-day fast seemed like a good way to dip my toes into the world of water-only fasting. Whether or not it was long enough to induce autophagy – I can’t say for sure. Be sure to check out my video/post for an in-depth look at the research on autophagy and what we actually know about it.
What I know is it was worth a shot to potentially reduce my risk of chronic disease.
Both my maternal grandmother and her sister died in their 50’s of colon cancer. Both my paternal grandparents suffered from heart disease and my dad had a heart attack and quadruple bypass last year. I – like the majority of people – have a family history riddled with chronic disease. I’m willing to try almost anything as long as it’s safe to ensure I live a long, healthy life.
So, with that said, a 3-day water fast seemed like a pretty non-invasive way to support my health!
Stick around until the end of the video and read on for more background on the science behind fasting and answers to common water fasting questions!
My 3-Day Water Fast Diary: Watch the video! >>
WHY TRY WATER FASTING?
While various types of fasting have recently become trendy, the practice actually dates all the way back to early humans. Unlike in our modern-day society, historically, food was scarce. Fasting was the norm and our bodies have been evolutionarily programmed to handle long bouts without food. Of course, we no longer have to endure long periods of time without food, but our genes haven’t changed much. Some medical experts believe that our current round-the-clock eating patterns may be contributing to chronic disease and that fasting may be the key to treating and prevent chronic disease.
In animals, prolonged fasting has been shown to prevent and reduce cancer incidence, diminish the negative side effects of chemotherapy, and increase lifespan.
During “prolonged fasting,” usually 72 hours or more, a process known as autophagy is believed to occur. Autophagy is the body’s cellular recycling process in which it breaks down damaged and dysfunctional proteins and other cellular components. Prolonged fasting is one way to induce this, though we don’t know exactly how long this takes in humans. Exercise has also been shown to induce autophagy in both humans and animals.
WHAT HAPPENS METABOLICALLY WHEN YOU FAST?
Our body’s preferred source of energy is the monosaccharide, glucose. Glucose is stored in the body in chains known as glycogen. During a fast, our body taps into our glycogen stores to get the energy it needs. Once the stored glycogen is used up (usually after about 24 hours), the body starts breaking down protein and fat. After about 48 hours, the body goes into a protein-sparing mode and relies predominantly on fat for fuel, turning it into glucose and molecules known as ketones to be used as energy. This adaptation is known as “ketosis,” the body’s starvation mode.
Without incoming nutrients, many physiological processes related to growth slow down. Fasting results in decreases in the hormone, insulin-like growth factor 1 (IGF-1). High levels of IGF-1 have been associated with chronic disease in adults. Fasting also results in decreased levels of insulin and leptin and increases in the fat-burning hormone adiponectin. Meanwhile, antioxidant and stress-resistant enzymes are activated in response to decreases in these hormones, which is believed to be one mechanism by which fasting results in disease prevention.
Additionally, some individuals report increased mental acuity during fasting. However, one study of a three-week ketogenic diet showed no differences in cognition and mood in healthy adult participants.
Note – you may have heard of ketosis in relation to the ketogenic diet. While short-term ketosis (which occurs during water fasting) may be beneficial for health and reducing disease risk factors, long-term ketogenic diets have not been shown to be beneficial for health, except in the case of severe epilepsy.
WHO SHOULD NOT FAST?
While it is perfectly safe for most people to do a short-term water fast, the following populations should not fast: pregnant and breastfeeding women, people who need to take medication, patients with diabetes, anyone who is underweight (BMI <18.5), children, and anyone struggling with an eating disorder.
HOW TO DO A 3-DAY WATER FAST
A 3-day water fast means that for 3 days, you will be consuming only water – no food and no other drinks. Decide when you are going to start and end your fast. You should plan it out so that you have at least 72 hours between your last and first bite of food.
Leading up to the fast, try not to overindulge. I ate ice cream at 9 pm the night before my fast. Bad idea. This just delays the inevitable. The goal is ketosis, which only occurs once your body depletes its glycogen stores. The more you eat and later you eat, the longer it will take to get to your goal.
I suggest having a small, balanced dinner in the early evening and beginning your fast after.
During the 3 days that you are fasting, make sure to clear your schedule as much as possible so you have time to rest, and you don’t have to worry about work, plans with friends, or anything else. I was surprised to find that I had bursts of energy where I was able to work, but there were moments when I felt weak and tired and needed to lay down.
Remember to speak with your doctor if you have had any health issues that may preclude you from trying a 3-day water fast.
HOW TO END A WATER FAST
Any fast should be broken with a light meal or snack, for example, a piece of fruit. For the following few days, it’s best to take it easy and avoid going overboard on heavy meals or caffeine and alcohol.
During fasting, the stomach’s production of hydrochloric acid (HCl) decreases because there is no food for it to break down. When you start eating again, your stomach needs to adjust to food again. Eating too much or consuming a lot of high-fat or very acidic foods and beverages could result in an overproduction of HCl and lead to painful acid reflux.
COMMON QUESTIONS ABOUT WATER FASTING
Can you have coffee while water fasting?
A water fast should include just that – water. Consuming coffee or tea activates the liver to detoxify caffeine molecules, so while your digestive system is getting a break, your liver is still working hard. That said, some experts say if it’s between not fasting or fasting with coffee/tea, use them.
Should you brush your teeth?
Yes! Your mouth has a microbiome, and you will still build up bacteria on your teeth, even if it isn’t from food.
Do you need salt/electrolytes?
Studies show that during a short-term fast, although sodium levels drop, they do stay in the normal range. However, long-term fasts (longer than 7 days) should be medically supervised to ensure the body does not go into starvation mode. To be safe, I’d recommend consuming a few bottles of electrolyte infused water per day or taking a daily multivitamin along with a pinch of salt.
What about ketoacidosis?
Ketoacidosis occurs when fat is being broken down too quickly, and it can cause serious health problems. Ketoacidosis is most commonly seen in patients with Type 1 Diabetes, but extended periods of ketosis can also trigger ketoacidosis.
While a short-term fast is generally safe for healthy individuals, fasting while dealing with other physical stressors including exercise, lactation, or low body fat percentage can cause ketoacidosis.
Be sure to consult your doctor if you have any concerns prior to or during a fast.
Do I need to worry about refeeding syndrome after water fasting?
Refeeding syndrome is an imbalance of electrolytes or fluids when nutrients are absorbed too quickly after a period of starvation. Refeeding most commonly occurs in people who have been chronically undernourished, have reduced physiological reserve (low body fat), or have suffered physical trauma including a stroke or heart attack.
Fasting for three days is highly unlikely to produce refeeding syndrome. However, it is recommended that people begin eating gradually, ~50% of typical intake, following water fasts that last for longer than 5 days.
Will I lose weight from fasting?
Depending on how long the fast is, you may lose weight. A 3-day water fast will likely result in minimal weight loss from water weight, while a longer fast may result in greater weight loss. Keep in mind that this weight will likely return when you go back to eating your normal diet.
I don’t recommend fasting for weight loss. What works for weight loss? A sustainable, healthy dietary pattern. Read my article on Weight Loss and Plant-Based Diets for more! >>
Can I exercise while fasting?
During a fast, the body is relying on stored energy, and we know that exercise uses up more energy. So, because the body is already tapping into energy stores and trying to conserve as much energy as possible, exercise is not recommended while fasting.
I recommend going on a light walk or doing gentle, restorative yoga if you’re jonesing for some movement.
Fasting sound too tough? There’s another option – ProLon Fasting Mimicking Diet.
PIN the post! >>
Weigh-in: Have you tried fasting? Would you try a 3-day fast?
Menopause Symptoms says:
Incredibly interesting and informative article! Once I was interested in the issue of fasting, but it didn’t go beyond ordinary interest. I never knew that this affects the rejuvenation of the body, although you have denied the significance of this fact, but it still stays a very interesting fact for me. Honestly, I would probably not be able to withstand three-day fasting, a maximum of 1-1.5 days. Perhaps you know whether there will be any sense in such fasting, if reduce the total amount of the days? I would really like to try it, but in my position, with menopause, it would be very difficult now, because I often have an uncontrolled urge to eat and depression. For three days without food, I will definitely eat my husband!)))
So interesting! I haven’t read up much on this so this was so helpful. You have me intrigued now to try this too!
Amanda Howard says:
I found this so interesting, loved your video diary of it and you were so inspiring how you got through it. Certainly something I’d love to try and do
About to embark on a 4 day water fast… usually I drink coffee during my fasts….looking forward to the improved water only fast… I am not new to fasting and I actually love the feeling it gives, it empowers my mind as well as my bod … Thanks Witney for confirming my thoughts about water only, so glad I found you….I have heart disease in my family history and am an avid reader on the subject of health…. I totally agree with the direction your taking your health and I will be a diligent follower… Thanx Phillip, I’m going to let your hard work PAY OFF FOR ME Thank You
Leopold Gering says:
Check out, “Beat the Heart Attack Gene: The Revolutionary Plan to Prevent Heart Disease, Stroke, and Diabetes”
Book by Amy Doneen, Bradley Bale, and Lisa Collier Cool
It was an interesting read.
Would be good if you could post about the after-effects you experienced both short and long term…did you notice an effect on your appetite?
Kanwal Bajaj says:
I believe the biggest challenge to doing a 3-day water fast is psychological and old habits. Doing this fast is also a way to practice self-discipline and develop will power
Hello all ,
Thanks for all helpful information you provided in
Today is my second day fasting in water .
First day was all good till I wake up 3 am with severe headache. I went to the toilet and I couldn’t stop not to vomit a lot of acid, after that I made a cup of hot water and I drank it slowly .I kept myself warm then I went back to bed.
today I’m feeling so much better ,I’m lighter definitely .
I start feeling fasting is helping cleaning my body. this is my second day and it’s nearly lunch time.
Santana e says:
I loved watching your process. Can you answer a few questions I have?
1. I Jazzercise daily, would you recommend stopping doing so during my fasting?
2. Would squeezing fresh lemon in my water break my fast?
3. I take vitamins day and night, would you recommend stopping doing so during my fast?
Thank you so much for your help!
Whitney E. RD says:
Hi there! If you’re taking the vitamins as prescribed by your doctor, you should continue them. Light exercise is likely ok but it’s best to rest during a fast. Unclear about the lemon – it’s likely so low in calories that it won’t “register” but there are no studies on this to verify. Hope that helps!
Rashidah Rashid says:
I am taking a hormones replacement medicine. Is it ok to do a 3 day water fasting while taking my medicines.
I know that you like to get the science right so you may want to note the following:
There is no scientific basis for the assertion that “ Our body’s preferred source of energy is the monosaccharide, glucose.“. I’m fact, there is very strong evidence that fat is our body’s preferred energy source. It is certainly more efficient.
Also, keto acidosis is a condition that occurs in the presence of high blood concentrations of both ketones and glucose, usually the result of poor management of type 1 diabetes. It does not result from nutritional ketosis (unless, of course, there is undiagnosed type-1 diabetes present).
Don’t forget that ketones are usable by the brain. The only other fuel for the brain as the ketone is small enough to cross the blood brain barrier. This is why there is research into ketone / mct oil as a treatment for certain forms of neural degeneration where glucose metabolism is a factor of the disease. I agree regarding ketoacidosis, only seen with the absence of insulin AND glucose ingestion; so the body doesn’t use the ketones, causing the ketoacidosis.
Two things stop me from trying a 3 day fast:
1. I take a blood pressure pill and a uric acid pill each day.
2. My wife insists we eat twice a day. If I try to skip even one meal, I’m in the doghouse for leaving her to eat alone.
So for now, it’s intermittent fasting. We do 17:7 every day and eat LCHF.
What negates this article for me is the casual use (twice) of the term the body’s “starvation” mode. The is so much disinformation around fasting and pressure from family and friends if one attempts to skip one meal and panic that one is going into starvation mode someone purporting to like to be scientifically accurate has fallen woefully short.
I have successfully completed an 11-day water fast. There is lots of good info out there about fasting.
I imagine you wouldn’t want to do a fast while you’re on your period, right?
Thanks. I was inspired by you. I did it! Surprisingly, I was neither craving for food nor felt any weakness. I had to endure disturbed sleep and a slightly heavy head!
I have been doing IF twice a week – both time and calorie restricted. Basically a 2-5. I started with 18 hrs – no eating after 12 noon until breakfast at 6 a.m. I just switched to 24 hrs – no eating breakfast to breakfast. Originally this was for weight loss but I have apparently developed neurosarcoidosis and I’m learning about autophagy so I did 48 hrs this week. It wasn’t bad at all. Based on your video and papers, as well as info from Peter Attia, I’ve read, I will try 72 hrs next month.
My question is – what about supplements? I take krill oil, 81 mg aspirin, alphalipoic acid, acetryl L-carnitine, D3, magnesium citrate, and B12. Should I stop taking them during fasting?
Also what about teas that do not contain caffeine?
Enjoyed the simple but very informative video. Will definitely continue to follow for health tips on dieting and fasting.
“Feeling like a kid before Xmas”!!! Loved it!! Thank you for this very informative 20 minutes! I feel more confident to start my water fast in a few hours. Wish me luck :)))
Did you weight yourself before and after?
How much water per day do u recommend