The most important point to make about occasional fasting is:  don’t do it for any reason without the prior permission of your personal physician.

There are all kinds of often fantastic claims about fasting, juice fasting, detoxing, colon cleanses, and so on that have been circulating for millennia.  How should we evaluate them?

There’s an important initial epistemological point worth making:

Distinguish knowledge from opinion.  Following Panayot Butchvarov [see The Concept of Knowledge], as I have argued elsewhere, in the proper use of ‘knowledge’ and its cognates, a proposition p is known if and only if mistake in believing p is inconceivable.  In other words, only the unthinkability of mistake is demonstrative evidence.

Nothing is known about fasting.  It’s not the kind of subject matter that is suitable for knowledge.

Therefore, all claims about fasting are opinions (beliefs).  Mistake believing any opinion is possible.  In other words, opinions are never supported by anything more than non-demonstrative evidence.

For that reason alone, it’s wise never to attach to any opinion; instead, keep an open mind.  As in other domains, detachment trumps attachment.

Furthermore, all opinions are relative to their perspective.  At best they can be only partial truths rather than the whole truth.

What opinion is reasonable about the wisdom of occasional fasting?

Occasional fasting may have consequences that are psychological or spiritual.  Because of their subjectivity, let’s here consider only the physical consequences of occasional fasting.

If only because there is some scientific evidence available, anecdotal evidence about the physical consequences of occasional fasting should be set aside.

Sometimes occasional fasting is used in a futile attempt to achieve physical consequences it cannot achieve.

The best example of this is using it to lose body fat.  Detoxing diets or fasting can result in the temporary loss of body weight.  Why does this occur?  The weight loss is due to water loss.  As soon as normal eating habits are resumed, the water weight returns.

Weight loss should never be a physical goal.  Body weight doesn’t matter at all with respect either to health or appearance.  What matters is your percentage of body fat.  Reducing that percentage is often a noble physical goal, but reducing body weight isn’t.

(What’s a good percentage for most people? 10 to 15% for men and 15 to 20% for women.  [Don’t confuse those figures with your BMI figure , which is a rather useless calculation.])

With respect to fasting, no long term period of fasting is justifiable with respect to its physical consequences.  Our bodies require fuel to flourish.  If you don’t nourish yours, you will die in a few weeks.

What, though, about occasional fasts?

‘Occasional’ here means ‘once every 6 months for 2 to 4 days.’

A “fast” means consuming no food and drinking nothing except water.  In other words, for example, a so-called “juice fast” is not a fast; instead, it’s a weird diet that relies on carbohydrates, which become sugar when digested.

(I never recommend drinking juice.  Eat an orange instead of drinking orange juice.  Eat a prune instead of drinking prune juice.  Eat an apple instead of drinking apple juice.  And so on.

Furthermore, except for organic berries, it’s usually not a good idea to eat fruit at all.  There are no important nutrients that can be found in fruits that are not also found in vegetables.  An occasional [e.g., once a month] serving of fruit may be enjoyable and somewhat beneficial, but regular servings are not for those who are overweight or obese.)

2 reasonable conclusions about occasional fasts

First, the major physical problem with respect to occasional fasting is that it results in a loss of muscle mass.

The more muscle mass you have, the higher your metabolic rate.  The higher your metabolic rate, the more normally you can eat without worrying about an unhealthful increase in your percentage of body fat.

If you lose 4 pounds during an occasional fast and 2 pounds of that is muscle mass, you will have, unfortunately, lost 2 pounds of muscle mass.

It’s difficult to increase muscle mass.  Doing so significantly requires doing regular, intense strength training like squats and deadlifts in the gym and getting proper rest and nutrition outside the gym.

For these two reasons, it’s generally wise to be very careful about doing anything that decreases muscle mass.

Second, the major physical benefit with respect to occasional fasting is that it may be a natural intervention that triggers stem cell self-renewal.

Consuming no food and drinking only water for 2 to 4 days once every six months may clear out old stem cells and stimulate new cells to be born.

That may be a benefit that is sufficiently powerful to compensate for the decrease in muscle mass.  Again, consult with your physician.

As for thinking that detoxing or cleansing or fasting is going to yield any other physical benefits such as weight loss or improved digestion, think again.

With the possible exception of an occasional fast twice a year, focus at least nearly all the time on eating or drinking well. 

(What does that mean?  I’ve discussed that in print in multiple places in addition to the physical well-being category of my blog on well-being [].  See also, for example, the website and some of my books such as Compulsive Overeating Help.)

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