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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 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!

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.

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