The practice of fasting has been around for thousands of years. Often it includes abstaining from food and drink for a period of time. However, with a water only diet, food, but not water is excluded. In recent history this practice has become a popular way to lose weight quickly. Some studies have shown potential benefit from water fasting such as lower risk of some diseases. It also seems to also help your body recycle old cell parts.1,2 The truth is however, that there is very limited research on water fasting. In addition, there are health risks that should be considered. In short, it is NOT for everyone.
What is Water Fasting?
Most fasting lasts anywhere from 24-72 hours. It really isn’t a good idea to go any longer than this. You might go on a water only diet for religious reasons, to lose weight, to detox, for health benefits or in preparation for a medical procedure. These are all great reasons and more and more people are water fasting for the health benefits.
Several studies have suggested some notable health benefits to a water only diet. Lower risk of cancer, heart disease and diabetes are a few of the biggies.1,2,3 But it also promotes a process by which your cells break down and reuse old parts. This is important because these old, damaged parts can be hazardous.4 You may have heard of lemon juice detox cleanses which uses the same idea. It prescribes a mixture of water, lemon juice, maple syrup, and cayenne pepper multiple times daily for up to 7 days.5
Proper Water Fasting
First, there are no science-based guidelines of water fasting. Nevertheless, there are some groups of people that should NOT do it. Anyone with gout, either type of diabetes, kidney disease, eating disorders, the very old and very young and pregnant women.6,7 Even if you aren’t one of these folks, fasting is hard and so you should begin preparing a few days prior. This could include eating smaller meals and fasting for only one meal.
During Your Water Only Fast
Remember, this is WATER ONLY for 1-3 days, so you want to drink plenty of it. That means 1-3 liters per day and more if you find yourself in conditions that use up more water. Examples of this include talking a lot, non-resting activities or hot weather. Again, it is not a good idea to do this longer than 72 hours unless supervised by a doctor. There are health risks, even for otherwise healthy people, particularly the longer the water fast. In fact, you are likely to experience dizziness, weakness and even mild disorientation during your fast. Thus, it is a good idea to avoid some activities. For instance, its probably not a good idea to re-shingle your roof or operate a backhoe while water fasting.8
After Your Water Only Fast
You will be very hungry after your fast, even if it is only for 24 hours. But you should not give in to the temptation you will experience to gorge yourself. Purposely eat a small meal and wait a couple hours to eat more. Otherwise you will have some serious digestive problems. You probably want to focus on carbs and fats as well. A lot of protein after a fast can cause problems. This is more important the longer your fast is.
When you do a water only fast, you literally cause chemical changes in your body. Eating a large meal can cause this chemistry to rapidly change and trigger refeeding syndrome. This can kill you as fluids and electrolytes rapidly change and damage cell function.9 You can expect to take the number of days to build up to normal meals as you fasted. In other word, if you fast for 2 days, you should take 2 days to slowly work up to a normal meal size. Don’t overlook this as refeeding syndrome is real and potentially fatal!
Benefits of a Water Fasting
There are several studies that have linked water fasting with health benefits. One of the most prominent is autophagy. This is the fancy term for cells breaking down and reusing parts that are otherwise old and damaged.4 This process seems to protect against diseases such as Alzheimer’s and heart disease.10,11,12 In other words, if your cells do not do this properly, your risk of these two diseases is higher. Your cancer risk is also connected to autophagy. When old cell components build up, cancer can result because these parts ‘get in the way’ and prevent proper cell function.13 Animal studies consistently show that water fasts promote this process. It may even increase your lifespan!1,3,14 Most studies have been on animals, not people, so it is hard to be sure a water fast will promote autophagy in humans.
Water Fasting May Also Lower Blood Pressure. Research indicates that this is the case with longer fasts.15,16 For example, in one study, 68 participants did a water only fast for almost 14 days. Don’t worry, they were under medical supervision! In any case, 82% of them, after this one single fast, lowered their blood pressure down to 120/80 or better. The average decrease was 20 points for systolic pressure and 7 points for diastolic pressure.15 In other words, on average, they started out at 140/87.
Another study found a similar result for folks fasting for 10-11 days. They all had high blood pressure to start with, but 90% of them dropped to 140/90 or better. This reading is considered the lower limit of high blood pressure. Their systolic pressure decreased an average of 37 points; much greater than in the previous study that included a longer fast.16 There are no studies on short-duration fasts and blood pressure.
Insulin causes the body to uptake sugar while leptin controls your feeling of fullness. Both are significant hormones that effect body chemistry.17,18 According to research, when you water fast, your body becomes more sensitive to these hormones.19,20,21,22 In other words, they work better. Your body becomes more effective at managing blood sugar levels and controlling hunger. Both imply a protective effect against obesity or even becoming overweight.23,24
Diabetes, cancer and heart disease are among disorders that might be avoided better as a result of water fasts.2,25,26 One study of 30 people who only fasted for 24 hours found lower levels of cholesterol and fat in the blood. Both are intimately connected with heart attack, stroke and heart disease27 Other studies suggest that water fasting protects the heart from free radical damage.2,28 Free radicals are basically toxic byproducts from cells that can cause damage. They are known to cause chronic disease when left unchecked.29 Furthermore, fasting may inhibit genes that normally help cancer cells to thrive and may improve the negative effects of chemotherapy.30
The Dark Side of Water Fasting
Wait a sec, isn’t weight loss a benefit of water fasting? Yes, but the type of weight you lose should be considered. Typically, you will lose as much as 2 pounds per day on a water only diet, but much of that is in fact water.7 You will burn carbs as well, but a lot of muscle mass also. Your body is in the business of survival and it lasts longer with more fat and less muscle. You must understand that you are literally starving your body on a water fast. The longer you do a fast, the more your body will try to preserve fat while using muscle for energy.
It seems a little counter-intuitive to think that a water fast will dehydrate you, but it is a real risk. Although you might not realize it, there is water in food too. Much of your normal water intake comes from what you eat, not what you drink.31 So not only do you need to drink plenty during a water fast, you also have to make up for the roughly 30% of your daily water intake that comes from food.
If you don’t drink enough, you could experience dizziness, nausea, headaches, constipation, low blood pressure or low productivity. Since some of these symptoms can come just from fasting, you should drink tons of water during a water fast.32 One good way to tell if you are drinking enough is to look at the color of your urine. If it is yellow, drink more. If it is clear or close to clear, you’re getting about the right amount.
Without getting too medical terminology on you, this basically means your blood pressure drops when you stand up. This is common among fasters.33 It isn’t particularly serious, but when you stand you may feel light-headed, dizzy and you may even faint.7,33,34 Really this can be expected while you are fasting, but again, you may not want to be driving or working on the 12th level of scaffolding of a skyscraper. If this is a problem for you, then fasting might not be for you.
Worsening Medical Conditions
You probably should not water fast if you are not in good health anyway, but some conditions definitely are a problem.
- Gout – A water only diet can increase uric acid production. If you already have gout you know how much of a problem this is.7,35
- Diabetes – Either form of diabetes amounts to an inability of your body to manage blood sugar properly. Any sort of fast will only worsen this.36
- Kidney Disease – Keep in mind that your kidneys filter your blood. People with kidney disease are already having problems with theirs and recall that fasting alters body chemistry. This will not help your already dysfunctional kidneys..37
- Eating Disorders – Fasting can sometimes encourage eating disorders, particularly in teenagers.38 It certainly won’t help if you already have problems with eating properly.
- Heartburn – Although some heartburn isn’t the end of the world, you are likely to experience it during a water fast. Your stomach is still making stomach acid, hoping for some food, but there is none to neutralize it.39
Will I Burn Fat While Water Fasting?
The short answer is no, not really. Of course, you will burn some, but like I said before, most of it will be carbs and protein from muscle.7 You will lose weight and lots of it, but if fat loss is your goal, you’re going to be disappointed. That being said, you can still incorporate fasting in a way that will burn more fat. Intermittent fasting or fasting once or twice a week for a short period (12-16 hours) is one way. Another is to fast by severely restricting calories. For instance, you might eat normally one day and the next day only consume 500 calories.40,41
Your body is made to go without food. Our ancient and even not-so-ancient ancestors fasted regularly as they simply didn’t have food all the time. You just may want to utilize that idea to burn fat rather than simply going without food.