Water Fasting: What Is It and Should You Do It?

Water fasting. What is it? Why do people do it? Is it safe? These are all the questions we had when we first heard about water fasting. Although new to western medicine, it's an ancient technique used in eastern medicine to detox and treat chronic diseases. Like every other diet "trend" that's out there, advocates share all the benefits, while opposers share the dangers. First, let's start with what water fasting is, the pros, cons, and if it's worth the effort.

What is Water Fasting?

Water fasting is exactly what it sounds like-- you consume only water for anywhere between 24-72 hours. Sounds intense, right? The effectiveness and safety of this new "diet" is highly debated. Since not much medical research has been done on the science behind water fasting, the health benefits and side effects are still not fully known.

While opinions on water fasting vary depending on who you talk to, what we do know is this: certain groups of people should be very cautious when water fasting. People with gout, diabetes, chronic kidney disease, eating disorders, older adults, pregnant women, and children have a high risk of negatively affecting their health by doing a water fast. If you fall into any of these categories, seek advice from a healthcare specialist, nutritionist, or doctor.

A typical water fast lasts between 24-72 hours and you are not allowed to eat or drink anything besides water. Water fasts should never last beyond 72 hours without professional guidance; doing this can pose certain health risks. Depending on your needs, your water intake will vary. Most people drink two to three liters of water per day, or half their body weight in ounces. Some people have also claimed to feel dizzy or weak during a water fast, so it may be best to avoid operating heavy machinery and driving. Others see this time as an opportunity to rest, reflect, and start the healing process.

Post-fast Phase

Since you haven't had a substantial meal for days, food should be re-introduced into your diet slowly-- this is the purpose of a post-fast phase. The post-fast phase lasts for one to three days and is a period of time where you should resist the urge to eat a large meal... no matter how much you want to. This phase is crucial after longer fasts because your body is no longer used to large meals. If you decide to indulge, you may be at risk of refeeding syndrome, a potentially fatal condition where the body undergoes rapid changes in fluid and electrolytes1.

If you can't have an actual meal, then what can you have? It's recommended to break your fast with a smoothie or lighter meals. As you feel more comfortable, introduce larger meals into your diet. Always listen to what you body is telling you and adjust accordingly. If you need to extend your post-fast phase longer than three days, that's completely okay!

Benefits of Water Fasting

Even though research is limited, studies have shown that a water fast has some potential benefits.

Stabilize Insulin, Leptin, and Glucose Levels

Insulin and leptin are hormones in your body that affect metabolism. Insulin helps your store nutrients from the bloodstream, while leptin helps you feel full. Research has shown that water fasting can make your body more sensitive to these hormones. Greater sensitivity = higher efficiency. When insulin is more sensitive, it means that your body is more efficient at reducing blood sugar; when leptin is more sensitive, it means that you body processes hunger signals more efficiently, which in turn, lowers your risk of obesity1.

It's said that this is the best benefit that water fasting has to offer. Along with becoming more sensitive to insulin, your body also learns to control it, along with glucose. When your body has constant spikes in insulin and glucose, it never burns its own fuel. When you eat, testosterone levels drop, causing glucose and insulin levels to spike; this causes inflammation and aging. However, your eating habits change during fasts, teaching your body to feed from itself and maintain optimal glucose levels3.

Promote Autophagy

Research from animal studies finds that water fasting may help promote autophagy. Autophagy is "a process where old parts of your cells are broken down and recycled1," or also known as "self-eating3." Cellular debris is removed and bad cells die off. During autophagy, your body "eats" the bad sells and proteins first, leaving only the healthy ones behind. Several studies have shown that autophagy may help protect your body from diseases such as cancer, Alzheimer's disease, and heart disease when kicked into high gear. Autophagy may also be the secret machine behind shrinking tumors, "vanishing" skin tags, dying viruses, and more. New cells also mean a revamped immune system. Dr. Valter Longer's study showed that a 4 or more day water fast can reset the immune system. As you age, your blood contains too many memory T-cells and not enough naive T-cells. Like the name suggests, you need more naive T-cells to fight off new challenges or diseases. Water fasting completely rebuilds your immunity with brand new naive T-cells.

While this sounds promising, there are very few human studies on water fasting, autophagy, and disease prevention. More research is needed before water fasting can be fully recommended to promote autophagy.

Lower Blood Pressure

Research showed that longer, medically supervised water fasts helped people who suffer from high blood pressure lower their blood pressure. In one study, 68 people who had borderline high blood pressure participated in an aggressive 14-day, medically supervised, water fast.

Although aggressive, the results paid off. 82% of people saw that their blood pressure fell to healthy levels, which is around 120/80 mmHg. On top of that, the average drop in blood pressure was 20 mmHg for systolic, or upper value, and 7 mmHg for diastolic, or lower value. That's significant!

In a separate study, 174 people with high blood pressure water fasted for an average of 10-11 days. Results showed that 90% of people reached a blood pressure lower than 140/90 mmHg-- this is the benchmark used to diagnose high blood pressure. The average fall in systolic blood pressure was 37 mmHg!

However, there are no human studies that link short-term water fasts to lowering blood pressure.

Dangers of Water Fasting

Everything has its side effect, right? Water fasting definitely has some health risks that you should learn about and consider before you commit to trying it.


Ironically, a water fast could cause dehydration. Seems contradictory, but 20-30% of your daily water intake actually comes from the foods you eat1! If you don't increase the amount of water you usually drink, but cut out foods, you may not be getting enough water. Symptoms of dehydration include dizziness, nausea, headaches, constipation, low blood pressure, and low productivity. If you notice any of these symptoms, it's crucial that you drink more water than usual.

Orthostatic Hypotension

Orthostatic hypotension is a drop in blood pressure and happens when you suddenly stand up-- you may feel dizzy, lightheaded, and on the verge of fainting1. This is really common in people who fast. When suffering orthostatic hypotension, you need to avoid operating heavy machinery and driving, which may significantly interfere in daily life. If you begin to experience these symptoms during a water fast, then it may be best to stop if you don't have the downtime to spend at home.

Worsen Pre-existing Medical Conditions

Some preexisting conditions may worsen with water fasting. People with these medical conditions should consult with a physician before starting a water fast:

  • Gout: Water fasting may increase uric acid production, which increases your risk for gout attacks
  • Diabetes: Water fasting may increase the risk of adverse side effects of both type 1 and type 2 diabetes
  • Chronic kidney disease: Water fasting may cause further damage to your kidneys
  • Eating disorders: Water fasting may encourage eating disorders, especially in teenagers
  • Heartburn: Water fasting may trigger heartburn-- your body may continue to make more stomach acid than usual without any food to digest

Lack of Nutrients

According to Whitney Linsenmeyer, Ph.D., R.D., spokesperson for the Academy of Nutrition and Dietetics, and instructor in the department of nutrition and dietetics at Saint Louis University, you are depriving your body of nutrition when water fasting. When depriving your body of nutrients, your metabolism shifts into a "fasting state," which is also known as a precursor to the "starvation state." This is when your body recognizes that it's not getting what it needs, and resorts to using stored protein and lipids. Even in the 24-72 hour window, Dr. Linsenmeyer says that water fasting can quickly become dangerous. Lack of nutrition for extended periods of time can result in mild symptoms such as fatigue, irritability, anxiety, drop in blood pressure, heart arrhythmias, confusion, seizures, or even loss of consciousness2. It's your body's way of telling you that it doesn't have what it needs to function properly and it's miserable.

Is It Worth It?

The decision to try water fasting is ultimately up to you. Some have found healing through water fasting. Although highly discouraged in western medicine, water fasting was used as a method for healing in eastern and alternative medicine for thousands of years and is highly promoted by True North, a California-based health center. Many of their fasting patients end their fast feeling enlightened, happier, and some are even rid of chronic pain!

Jordan Younger of Balanced Blonde tried out a 2-week long water fast after suffering from imbalanced hormones, eczema, uterine cysts, and more. True North assisted her through the whole thing, and even after the body aches, shakes, and dizziness, she said her entire approach to life has changed. Her rashes are gone, energy feels unlimited, and she's thriving. Isn't that what we all want? Ben Marcus, writer at GQ, documented his 6-day long water fast journey as well. He, too, experienced extreme fatigue, restlessness, and aches, but agrees that water fasting made him a new man. His chronic pain that stemmed from an autoimmune disease was GONE at day 6. However, the true test of the effectiveness of a water fast is the long-term affect. Even after you're done, True North recommends that you stick to a fully plant based diet and cut out any processed foods. This may seem impossible or unrealistic to some, but if kept, you may reap some of the long-term benefits doctors say water fasting has.

Even with these success stories, the dangers of water fasting should always be considered. Be smart about it. Take the testimonials with a grain of salt, do your own research and always consult your doctor before trying any type of fast or diet. If you've water fasting, let us know what your experience was like! We're always reading the comments blow!