Why Starvation And Fasting Are Good For You


Recently I wrote a post about cleanses and detox diets that had this comment:

You say that skipping a meal occasionally, juicing for a few days or fasting for a day is beneficial..says who? Do you have evidence of that?

That was from Heather Carey.

Okay, so here goes.

But of course, I’ll start with a disclaimer:  I’m not a doctor!  Nothing I say constitutes medical advice.  Nothing I’m going to write should be interpreted as a specific diet recommendation, just condensed info to allow you to think about your health in a meaningful way. 

Starvation and Health: Connecting the Dots

All living organisms are equipped to survive in periods of stress.  Maybe long periods of time.  The basic mechanisms of biological survival are very well conserved, and many of the pathways involved in energy utilization, aging, and cellular degradation have a high degree of similarity throughout the biological kingdom.  Not just in primates, but in mice, flies, yeast, and in some cases even bacteria.   For example it’s estimated that insulin (the chemical primarily responsible for storing energy) is at least 1 billion years old.

Dietary Restriction

One of the best established facts in medical literature is that dietary restriction (reducing calories by about 20-40%) promotes longevity and reduces your chances of cancer, diabetes, and most other forms of the metabolic syndrome.  This has been known for about 30-40 years and has broadly proven to be true in all organisms it’s been tested on, including humans.

When your body is put under physiological stress it’s forced to recycle old proteins into new ones, eat up organelles that are no longer serving any purpose, and reduce the hormones that make your cells want to grow.

In science literature this effect is called autophagy, and it’s probably an irreplaceable component of good health.  All these effects are the same reason exercise is good for you too, but it’s counter-intuitive to think that our eating habits can trigger the same sorts of effects since “Three meals a day” has been beaten into our heads since birth.

Life Used to Be Random

Most of the volatility our instincts have been conditioned towards have been sucked out of everyday life, for better or worse.  Our body’s mechanisms for energy conservation were formed when food availability couldn’t be taken for granted, and we simultaneously had to make our energy last us as long as possible but still be ready on a moment’s notice in case something dangerous happened.

Eating and exercise were non-linear, fractal, and difficult to forecast.  Not anymore.

The Forgotten Fuel

The human body can live up to 40 days without food.  Your muscles store enough glucose to last about 2 days.

When your body senses that food is scarce it begin turning your fat tissue into a compound called beta hydroxybutyrate (BHOB).  Utilizing BHOB for fuel used to be thought of as a bad thing since the only time people seemed to use it was when diabetics went into ketoacidosis, which happens when your body can’t produce enough insulin so it can’t stop secreting glucagon, which causes your body to inject ketone bodies into the blood, which makes it more acidic.   Drastic changes in your body’s acidity level aren’t good, so BHOB was thought of as a toxin.

However, that’s an extreme case that happens due to disregulation.  Under normal conditions of scarcity utilization of BHOB is normal and healthy.  In many ways it’s more efficient than glucose since it gets turned into ATP more efficiently and your heart in particular has an affinity for BHOB as a fuel source.

Alzheimers and dementia are beginning to be seen as “type 3 diabetes,” and it appears that brains that are overfed on glucose lose their ability to respond to insulin.   In fact one of the most foolproof ways to treat alzheimers to make the brain more “ketogenic” so it can split its fuel consumption between glucose and BHOB.

BHOB is the fuel source of starvation.

Fasting and Starvation is Good for Cancer

Anyone who’s experienced a loved one that has cancer knows that chemotherapy can be just as dangerous as the disease itself.  Chemotherapy drugs by their very nature are toxic and it’s hard to make sure they only treat the cancer cells.

Valter Longo is a scientist at UC Davis who showed mice with a wide variety of cancers respond much better to chemotherapy (ie, the good cells don’t go with the bad) if they’ve been starved for 2-3 days before undergoing treatment.

This “starvation priming” effect has been replicated in the other animals we usually do tests on (nematodes, fruit flies, c. elegans), and the effects have all been the same.  In fact, one study found that the survival rate for “good” cells improved over 1000x with a little bit of starvation!

These sorts of treatments are beginning to get rolled out on humans and so far the results are promising.

Humans Have Been Fasting for 1000’s of Years

Every religion that I know of has some sort of ritualistic fast that requires its members to deliberately do without various types of food.  They all differ in their flavor, but all center around a few common principles.

Basically they replicate the non-linearity and randomness of food consumption that’s so important to our health but hard to come about in our day-to-day lives.

I believe in the horror stories about people who try and “binge” diet and things go totally awry.  I’m inclined to believe they get half the story wrong, not all of it.  A little bit of timely deprivation can do the body a lot of good, but it’s what they eat afterwards that messes everything up.

What’s The “Right” Amount for This Sort of Thing?

So far this article is about 1000 words strong with me yapping about the various benefits of deprivation and that leads to the natural question:

How much should I do this for myself, if at all?

The important point here is that the benefits are non-linear.  This means the most important ones occur occur in the early phases of the process, not at the end.  It’s the flipping of the switch that’s useful, not the days and days of struggle afterward.  Benefits usually taper off after a few days and it eventually becomes harmful if it goes on for too long.

A little bit of deprivation does the body a lot of good, but too much will make you weak.

In most studies the fasting will happen for 2-3 days, but that doesn’t mean that’s the “right” amount of time for everyone.  There is no one size fits all for this sort of thing, just best to do what feels comfortable (but not too comfortable!) for you.

Personally, I just try and mindfully skip a meal from time to time and/or plan a few days when I’ll have a nice breakfast and refrain from food until after sunset.

6 thoughts on “Why Starvation And Fasting Are Good For You”

  1. Hi Jonathan, thanks for quoting me in your post! I feel compelled to reply again and keep this conversation going. Let’s just say for example, that fasting is proven good for you (just FYI, I looked at your studies and, yes, there are many people who fast for religious reasons that has nothing to do with health. Your studies mostly look at mice and monkeys in EXTREMELY controlled environments, and for every study you found that shows a positive correlation towards starving and longevity, I can show you one that disproves it). And it is recommended now that we all reduce our caloric intake to 1,000 calories a day. You and I both know that 1,000 calories doesn’t get you very far, especially if you eat like most of the people in the United States. Making those calories count becomes crucial to your survival as well. You cannot mess around with what you eat, it would have to be very well planned out (we already screw it up enough with our out of control sugar intake, hence the type 3 diabetes epidemic). My point is that, beyond not being proven (seriously, show me a more credible human study) it is totally unreasonable. And just because you might believe that “starving” yourself is helpful, I am curious to know what you think the benefit of skipping an occasional meal does for you?


    1. Heather,

      In general, I think the vast brunt of literature points to the beneficial effects of caloric restriction on health, even if the specific mechanism is unknown. To say otherwise is really swimming against the tide IMO.

      However, I don’t think the take home point is that we all have to be eating 1000 calories a day or else. Like you, I doubt that would work, and is probably not necessary for getting from point A to point B.

      Which is why I find fasting interesting, because at least some of the benefits are derived independently of the lack of calories themselves. Ie, the non-linearity of feeding itself seems to provide some kind of benefit regardless of total caloric intake.

      Here’s a very good summary paper of various studies that have been done on Alternate Day Fasting:

      It’s obvious that there are more good papers on animals than on humans, but in general the studies done on animals have shown more consistently positive results. You can interpret this in a variety of ways, but I’m inclined to think that there is good reason to think occasional deprivation is good for us, under the right conditions.

      There is not a smoking-gun study that says “Ah-hah! Jonathan’s right!”, and I don’t think it’s mandatory (it would probably NOT be a good idea under a variety of lifestyle circumstances), but it’s equally incorrect to dismiss it as simply being hooey when I think the breadth of evidence about our metabolism, endocrine system, and various epidemiology studies support the basic idea that alternations between the “fed” and “fasted” state is very good for our health in one way or another.

      And for many, a planned day or two of restraint filled with leisurely walks might be more feasible than gym visits 4 times a week.

      FWIW, here’s a recent paper that studied ADF on people for 12 weeks (longer than most other human studies up until this point):


  2. I totally agree with you. Humans weren’t meant to have access to enough food. I regularly eat a small amount of calories and engage in endurance exercise (like in our days of hunting/gathering). Every once in awhile, I’ll eat a really big meal. I find that this method works the best for me. I know everyone is different, though.


  3. There is an old article about a type of diet called the abcde diet (check it out). It never really took off but I lost fat, gained muscle, got much stronger, amazing endurance and had ‘beneficial’ mental effects. I looked like and could compete with professional athletes, within a few months I went from doing the 100m sprint in 15 secs to under 12 secs, this is without any increase in exercise or activity.

    It was basically 12 days of starvation followed by 12 days of overeating. It’s very hard to follow and apparently it didn’t work for some people, everybody is different.

    The key part of the diet was taking advantage of a persons hormonal response. He had studies to back his reasoning up – although the legitimacy/relevance of those studies has been questioned.

    Basically when you overeat your hormones change to a beneficial ratio for muscle building over fat gain BUT this benefit begins to tapers off at around 12 days, so just as the beneficial effects are at their peak, you drastically cut calories while your body is still optimised for fat loss and muscle retention.

    Hopefully during the overeating phase you put on more muscle than fat and during the undereating phase you lose more fat compared to muscle was the general idea.

    The focus was on manipulating sex hormones (testosterone first and foremost) but I think it’s likely that during the undereating phase you were essentially resetting the sensitivity of many other receptors – especially insulin receptors. The body also likely repairs any DNA damage done and the body goes into repair and salvage mode on the cells of the body. Then when you overeat most of the food you eat goes to the strengthening and production of essential cells and organs e.g. muscle/heart/brain but without the negative effects of prolonged overeating where the body becomes lazy and desensitised to important transmitters. I assume that many of the beneficial effects of calorie restriction might also begin to taper off in a similar time period as the sex hormones.

    I never really thought of this diet in relation to health and longevity but just physical ability and weight but I wouldn’t be surprised if it’s a better method of straight/intermittent calorie restriction.


    1. Nick,

      I agree that this diet probably has clinical relevance, but is probably impossible logistically for most people today. When you fast your body begins something called autophagy, which is basically when your cells start eating themselves. This is basically like hitting a reset button inside your body, which increases your sensitivity to various hormones, including insulin and testosterone. It’s also why the ketogenic diet is good for some people: the low carb environment mimics fasting without the reduction in calories. Although just for reference the ketogenic diet is also not a savior either, see why here:

      So I think your line of thinking is basically on the right track.


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