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Should You Fast One Day A Week?

I'm often asked if fasting one day a week is good for health? To answer this question, let's take a look at what happens in your body when you begin to ingest nothing but water.

After your cells use up the sugar that's in your bloodstream from your last meal or beverage, your body has to find another source of energy for your cells. The first places that it turns to are your liver and skeletal muscles. Both your liver and muscles store sugar in the form of glycogen, and when needed, glycogen can be broken down to glucose, which all of your cells can use to produce energy for their ongoing activities.

During a water-only fast, your glycogen stores are depleted within about 24 hours, give or take a few hours. After your glycogen stores are used up, most of your cells begin burning fatty acids for energy - these fatty acids come from your fat reserves, including fatty tissue that surrounds your organs.

Two groups of cells - your red blood cells and your brain cells - cannot use fatty acids to fuel their energy needs. Your red blood cells and brain require glucose, and once glycogen/glucose from your muscles and liver are used up, your brain and your red blood cells get their glucose from the following two sources:

  1. From glycerol, which is a component of your fat tissues.

  2. From your muscles - some of your muscle tissues get broken down, and the amino acids from your muscle tissues are used to produce glucose for your brain and red blood cells.

Clearly, it's not in your best interest to rapidly eat up your muscles to meet the energy requirements of your brain and red blood cells during a water-only fast. Your body knows this, and somewhere between the second and third day of water-only fasting, your liver begins churning out ketones, which, during a water-only fast, come primarily from the breakdown of fatty acids from your fat reserves.

Once your liver generates large numbers of ketones, your brain is able to use ketones to fuel itself. At this point, only your red blood cells require glucose that must still be derived from breakdown of your muscles, but with your brain no longer dependent on breakdown of your muscles for energy, the rate at which your muscles are catabolized will be such that your muscles are spared as much as possible - this state is called "protein sparing" - it's a survival mechanism that's built into human physiology to deal with times of famine.

Getting back to the big picture, it should be clear that from about the 2nd or 3rd day of a water-only fast, your body meets it energy requirements by burning through your fat reserves.

Since the bulk of the toxins in your body are stored in your fat reserves, the longer you fast on water only, the more fat you'll burn and the more toxins you'll eliminate from your system.

This is why we see elimination of lipomas, atheromas (accumulated waste in your blood vessels), and other conditions related to toxin accumulation during a prolonged water fast.

Put another way, your body does not experience significant detoxification during the first 12-24 hours of a water-only fast.

Your body begins to eliminate large quantities of toxins only after it begins to burn your fat reserves at a rapid rate. And this doesn't happen until you've used up the glycogen stores in your liver and muscles.

So when you fast one day a week, you deplete the stores of sugar in your liver and muscles, and you begin to break down your muscles - these are the main things you accomplish during the first day of water fasting. Significant detoxification only begins to occur if you continue past day one of fasting.

This is not to say that there are no benefits to fasting one day a week, or that you don't eliminate any toxins during a one-day fast.

You are eliminating toxins with every breath that you take. And your body will always increase its rate of ongoing detoxification whenever you get more rest and/or eat less food, because less digestive burden and more physical rest always mean more available resources for detoxification.

Rather than fast one day a week on water only, I think it makes more sense to do a juice diet one day a week, or even once a month. With a juice diet, you can supply your body with enough nutrients that you don't have to deplete the sugar stores in your liver and muscles, or break down a lot of your muscle tissue. At the same time, because the nutrients in freshly pressed juices are so easily digested, a one-day juice diet can ease digestive burden and enhance ongoing detoxification to some degree.

But let's be clear: the main benefit of a one-day juice fast is not significant detoxification; it's a concentrated period of rest for your digestive organs, and an opportunity for the organs that are responsible for ongoing detoxification - your liver, kidneys, skin, and lungs - to do a little extra health-promoting work.

To sum things up, I would say that it's not good for long term health to fast one day a week on water only. If you want to give your body a period of rest and intense cleansing once in a while, it makes more sense to spend a day eating all raw fruits and vegetables, or drinking nothing but freshly pressed juices. If experiencing this type of cleansing period is of interest to you, I recommend that you view the following series of articles:

Full Body Cleanse Series

You can also review the following guide to using freshly pressed juices to promote cleansing:

How Enhance Your Health With Juices and Juice Fasting

If you know anyone who fasts one day a week solely for health purposes, please consider sharing this article. Thank you.


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Thanks a lot for the information! I was contemplating on doing this but now I'm not so sure. I think I will have to read up on it more, maybe do a fast less often but maybe for 2-3 days? I'm new to fasting and cleansing the body though so I don't know where to start. Though I have been eating alot of vegetables lately. Plus I've tried a 2 day water fast as well.. Not fun with my acid reflux! Anyway, thanks alot again for the info, will keep it in mind.

One thing you have to realize with this article, and many more articles on fasting (pro fasting or not) is that there are no citations to professional studies or anything of the like. Don't jump on this guys bandwagon so fast! Sure, fasting once a week might not clean out as much toxins as fasting for a couple days a month, but once a week is much easier to track and it will also help you get out of those bad eating habits. I noticed that no one really mentions the stomach when talking about fasting. When you're on a fast your stomach will shrink. It will expand when you start eating again, but I find after a day of water fasting I'm not as hungry for the next few days and its easier to stay away from the junk and keep to healthy greens and proteins. Also, as for the losing of muscle, if you're contemplating a fast I'm assuming you're trying to lose weight rather than pack on the pounds. If you continue to workout and exercise, as well as eat plenty of protein, throughout the rest of the week you wont see any muscle loss. You may even see muscle gain! Well, good luck and remember to drink lots of water!

Steve, this is exactly what I was thinking! No scientific studies is a big one for me.

I've just decided to start fasting once a month [eat dinner one day, don't eat the next, eat breakfast - about 40 hrs]. I'm curious to see how it affects my weight in the long run and grocery bill [yep, I'm a student].

I used to do the 30 hr famine every year in high school. I remember afterwards they would give us a slice of pizza to 'celebrate' that we had made it. That one slice always filled me up. I just finished my fast for this month and I can't even finish a sandwich. Stomach shrinkage is a big thing for me when I fast.

I've been reading a book about diet and human health called 'The Pleasure Trap'. It describes in detail the process and benefits of prolonged water only fasting.

Animals do this instinctively when sick, which promotes healing and detoxification processes that happen automatically whilst water fasting. Humans are no different.

The only thing that is different for humans is our culture and the way conventional medicine is defined by Capitalism/Big Pharma.

Water only fasting is incredibly useful. It can reverse certain types of diabetes, dementia and ageing. It can halt auto immune diseases and reset a person's appetite so they eat less junk food afterwards and instinctively look after their own health more.

Water only fasting is like a potent reboot. An important aspect that must not be ignored however, is that longer periods of water fasting need to be medically supervised.

I so much agree with Steve about everything he mentioned!
For me, water fast once a week is much more effective, than the juice one.
Sometimes, when I feel lazy for 36 hours fast - I go for 24 hours fast. But still every single week.
Works great for me though. In all aspects!

well, juice fast is great but this is not real fast :)
Nothing would clean you up as much as water fast, but I agree with this article 1 day is a little short, to get real benefits 3 days is way better.

You won't gain muscle if you have a calorie deficit. To understand that and what the article is talking about a simple scientific study won't suffice. You'd need to educate yourself in higher levels of physiology and metabolism than what is learned at the high school level. An exercise physiology text or an advanced nutrition text from the library are good choices to start with and will have citations for studies in them :) I'm not a doctor but I do have a degree in kinesiolgy and health science. Take care!

You are totally incorrect in your theory. An obese person can gain muscle whilst losing fat as even though they have a low intake of calories the fat stores are used as fuel, so as long as the protein content of their low calorie diet is moderate there will be muscle gain. This has been proven time and time again the human body is more complex than doctors understand and also there are many bodybuilders natural and drug assisted who gain great physiques using intermittent fasting.

You might be right on a micro scale. The day that you're fasting you probably aren't gaining muscle. But on the other 6 days of the week it's entirely likely you aren't operating at a caloric deficit in which case muscle gain is totally possible.

I've learned so much over the years about the fasted state. The doctor is right on the money with everything. He's actually generous and says 2-3 days ketosis kicks in but I've read it's more like day 3-4. He also didn't mention that even though the brain is running on ketones, it's still requiring 1/3 of its energy from glucose via muscle protein breakdown. I do agree that long term 24 hour fasting is unhealthy because of the muscle loss that occurs around hours 16-20 (dependent on the person). I would simply say this, around 18 hours of fasting have a few protein shakes to ensure you're sparing muscle. Otherwise if you're hellbent on a water fast then do it for a week once a year, medically supervised. That way you only dip into your muscle tissue at one period as opposed to 52 times a year.

This is not a medical advice. It may not be a safe option for you. Please contact your physician for personal advice. I am 50 year old 6’1″(185cm) male, medical doctor. Over years I had my weight gradually reached 310 lb. (141kg). I started very low carbohydrate diet in 2014. After initial weight loss of about 40 lb.(18kg) I gained it almost all back. In 2015 since I did water and salt fast for 30 days without significant effort since I was already in ketosis already for quite some time. I drank water whenever I wanted it and took salt from hand whenever I wanted. In order to retain that water I need to take salt. I also dissolved Centrum Silver multivitamins in water and drank it couple times a week. I continued to work as a physician in a very busy practice. After 30 days I stopped fasting because I felt weak and had difficulty concentration at work. To break my fast I avoided carbohydrates, (no sugar, no fruit, no juice, and no starch). People have complications from re-feeding because glucose raise in blood stimulate insulin production and severe electrolyte shift in the body that may cause irregular heart beat and very rarely death. I ate small amount of broth, eggs, cheese. I took Thiamin, Magnesium Oxide, Potassium Chloride and Potassium phosphate for the first several days.
In January 2016 I fasted for 35 days. I consumed water, salt, multivitamins. I broke my fast with broth, milk, heavy cream, eggs, very slow, small amounts, and several days. Again, I supplemented re-feeding with Thiamin, Magnesium, Potassium, and Phosphorous. During that fast my weight went from 321 lb. (146kg) to 266 lb. (121kg). Since then I started fasting every first week of every month. I did nothing to break a week long water and salt fasting, no vitamins, regular activity, no exercise. I ate anything I wanted, but kept very low carb diet. Every month I gained about 30 lb. (14kg), then lost 22 lb. (10kg) during wasting week. It is quite easy to fast if you are on low carb diet. But it is not enough. Every month I gain 8 lb. (4kg), approaching my initial weight 321lb (146kg). Starting next month I will do two 6 days fast. On the first and 15th day of every month. This is not a medical advice. It may not be a safe option for you. Please contact your physician for personal advice.

I have been researching fasting and just completed my 2nd 24hr water fast in 2 weeks and I do find this really good for easing the pressure on stomach and bowel. I do feel quite light headed today (had dinner last night and breakfast this morning) and I am assuming this is a result of depleated glycogen. My research has certainly found and is supported in this article that a longer term fast of the kind mentioned in this article is far more beneficial especially if you do not want to loose muscle mass just body fat. As I understand it takes more than 24 hrs of fasting (3 to 4 days) for your cells to go into repair mode and start having any health benefit for disease. As mentioned here as well, I guess there is no quick fix to a cleanse and what we have taken years to pollute our bodys with may take years to undo with good healthy living and excercise.

Thankyou for this informative well written article.

Fasting is all well and good but I find colonic irrigation is the best way to rid the body of toxins.

I have fasted one day per week for extended period of time,once in a while I would do 2 days per week.What I found was my sense of smell,and my mind became extremely sharp I would experience a clearness in my head that was uncanny.Also I required less sleep and did not wake up groggy.The main thing that you have to be extremely careful about is how you break the fast ,it has to be broth,fruit,cooked vegetables something light and control the amount I found I had a tendency to over eat and the you will feel really awful it's almost like a drug induced stupor, I'm convinced that food is nothing more than a drug to the body because of how it makes you feel if you want to avoid that crappy feeling you can exist on a vita-mix machine my smoothies in the morning last me 5 to 6 hrs and consist of banana,raw almonds,chia seed,mixed berries,fresh spinach and cucumber , I use cashew milk instead of cows milk.I drink this in the morning and you can have a tiny lunch then for dinner I have another drink but smaller in portion an s piece of meat, I tell my wife that drink is my rocket fuel. I'm 66 and if I stick with this regime and along with my walk with Jesus I have been cured of some troubling problems and I don't get sick anymore even if my wife gets sick I won't catch it Fromm her as I used to which I find amazing.

Dr. Ben Kim said that long term one day fast is not good.

I would love to understand more and hear from Dr. Ben why long term one day fasts are not good for long term health.

But as per Ayurveda one day fast weekly and monthly is good. But certainly recommend longer fasts.

How longer fasts help, please see:,1787,2836&q=759

It is recommended over a period of two years two or three longer fasts, and to maintain once every five years a longer fast.

As far as scientific study is concerned, we may not find in the near future as it is quite expensive and no one is ready to sponsor such study. But by speaking with related experts one may find evidence, may be recorded as part of their practice.

I personally see lot of benefit with 16 hours gap, and eat only 8 hours during the day. I am eating as per my body requirement during this time.

Have fun,


You would be better off making fruit smoothies with the pulp. The fiber slows the digestion and mitigates the insulin spike. Juice is like soda with some nutrients in it. The nutrients are not enough to make it a good choice.


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