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.
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.
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Weigh-in: Have you tried fasting? Would you try a 3-day fast?