Is Fasting Beneficial?

Mr. D. S. of Saratoga, CA asks: Hunter-Gatherers eat natural food and exercise and get almost no degenerative disease. But they also fast, so shouldn’t we fast?

Great question. I used to think so, but had to change my opinion. In the past I encouraged fasting. My starting point was 24-hour fasts. In some cases I experimented with longer fasts pand different intervals between fasting in order to improve various blood markers and, interestingly, it often worked, but only at first. After regularly fasting for some period of time most of my patients’ bodies found some way to compensate, usually subconsciously. The numbers returned to their earlier values, and for some, actually got worse and were accompanied by fat weight gain. So starting about 3 years ago, I began advising people not to fast. There are exceptions but we humans do not take lightly to fasting.  I know, I have watched many people over the course of years and with rare, very rare, exception fasting always backfired. The compensatory mechanisms are very subtle and very powerful.


This is a very good example of Quantitative Medicine. Logically, fasting should have worked. But it didn’t. The numbers define and quantify health and must be acknowledged, even if that means I have to change my recommendations.

There are two sides to fasting, one good, one not. The good side is that it gives the body extended time to clean out damage and to repair. I have seen profound examples of this in the past. However, the bad side is that fasting is a catabolic state. The body may well decide to conserve rather than repair; to tear down rather than to build up.

A second important point is the hunter-gatherer lifestyle itself. It is true that degenerative disease is rare in hunter-gatherer populations, but we need to identify the reasons for this. Certainly eating parasite-ridden food would not be a good idea. This could, and frequently would, kill you. The principle hunter-gatherer attributes that I believe worthy of emulation are: 1) a natural food diet, 2) frequent explosive exercise, 3) connectedness to their world and their community, and 4) getting a good nights sleep.

However, several other hunter-gatherer attributes are to be avoided: 1) parasite-ridden food 2) unavailability of treatment for infectious disease, 3) unavailability of treatment for wounds, 4) inter tribe warfare, 5) childbirth issues, and, recently added 6) fasting.

So again, it is good to take what cues we may from the hunter-gatherers, but each one needs to be examined for its own quantifiable merits.

The body has incredibly powerful metabolic regulation. It can shut down energy consumption if there is a food shortage, or, amazingly, if it detects anything that might signal that a food shortage is imminent. Skipping a meal is an obvious example, as would be a diet that featured calorie restriction, such as Weight Watchers.

Other activities can signal food shortages as well. For instance, if you are doing a lot of walking, a round of golf perhaps, the body may interpret this as migration, and why would you migrate? To seek a new hunting ground, so there must be a food shortage coming. The system shuts down.

  5 comments for “Is Fasting Beneficial?

  1. Sri
    February 5, 2015 at 8:11 pm

    Thanks Doc,
    This is exactly what I wanted to know


  2. Helene
    March 28, 2015 at 1:22 pm

    To fast or not to fast?
    For those who is fasting the picture doesn’t look rosy at all. Therefore, such good summation, as this one, based on evidence, should ‘re-surface’ from time to time. Than those, who may read it and who wishes to live healthier longer would use their common sense.

  3. Alexander
    November 5, 2015 at 10:50 am

    I am curious if you investigated the intermittent fast? That fasting program, as I understand it, consists of dividing the 24 hour day into a consecutive 8 hour period where you consume your meals followed by a 16 hour period of zero calorie consumption of which a portion of that time would be sleep at a reduced metabolic rate.

    Could just sixteen hours of adequate hydration without food coupled with dialed back physical exertion and sleep be beneficial for rest and repair of the body without triggering the bad aspects of fasting?

    What is your opinion of such an approach to “fasting”?

    • Dan
      May 22, 2016 at 7:07 am

      I’d like a response on daily intermittent fasting, too. It does seem to run counter to the book’s recommendation for three meals plus two snacks!

      I’ve transitioned to two meals a day, at noon and six, and it’s helped me lose some weight. It also prevents any worrying about “how much’: the only decision is “is it time to eat or not?”

      But since I’m just starting the QM journey, should I abandon this, then have the benchmark blood labs done?

      • May 23, 2016 at 8:39 am

        Hi Dan and Alexander,
        My clinical experience with fasting – different than my theoretical understanding – has found that almost(!) everyone winds up engaged in compensatory eating and that fasting winds up backfiring. They do great 2 or 3 or 4 cycles and then just slip into compensatory either over-eating or carb-snacking. Theory and practice diverge. This is in the long haul. I’ve seen wonderful changes at the 3-6 month mark and far worse at the 12 month mark so often that I’ve stepped away from fasting as a discipline I recommend. Everyone looks like a winner at 3 months and then worse at the year mark. Bulletpoints, magic lists, and quick fixes is not what QM is all about. Which brings us to the one to two meal a day diet types. Look at that ‘how much’ question; therein hides the fad and downfall. The older version of this – I’ve heard this one a thousand times – ‘I run so I don’t need to watch my diet and food intake.’ Your question deserves a longer answer but I can’t provide that here; have to go see patients. It would be best to see a true baseline – what your behavior has been like for the long term – before you test. Thank you for your note, Dr. Mike

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