What Happens When You Stop Eating
We live with the impression that something bad is going to happen if we don't eat every few hours. People think that they'll go into starvation if they skip a meal or two. But nothing could be further from the truth.
We are capable of extraordinary physiologic achievements - that is, if we challenge ourselves. But we don't.
Most of us eat at least 3 meals a day plus snacks. We never give our body a break from digestion, allowing it to focus more on processes like clearance of damaged proteins, increased DNA repair, and increased cellular waste disposal.
In the past I wrote about the experiment of David Blaine where he went without eating for 44 days. Read it here.
I also wrote about the longest medically recorded fast, in which a healthy obese man voluntarily didn't eat for 382 days. He only drank water and took some supplements here and there. He was under medical supervision. Read the post here.
The Five Stages of Fasting
There's a lot of mysticism and many religious connotations attributed to fasting. Aside of that, fasting has been extensively researched from a scientific standpoint. The decade of 1960s is considered the golden era of fasting experiments. Researchers would subject obese patients to water fasting. Today that is considered unethical.
I, lean subject, have subjected myself to 5 days of water fasting. I didn't die. Counter-intuitively I didn't experience hunger either. Most people who water fast report that hunger is gone after 24-48 hours of fasting. You may feel hungry until your body begins efficiently burning its own fat for energy. I'll discuss this in a moment.
I never actually felt hungry because I already habituated my body to rely on bodyfat for fuel. So my transition to the fasting mode was barely noticeable.
What's more interesting is that I went to the gym and did my usual lifting routine on days 1, 3, 5 without experiencing reduced performance. I wouldn't recommend this though.
Fasting makes sense from an evolutionary perspective.
Do you think that your average hunter-gatherer would have unrestricted access to food 3 times a day seven days a week - like we do today?
I'd suspect that they would mostly go through periods of famine (days without eating) and periods of feast - like after a successful hunt. Numerous research studies are in favor of this hypothesis.
Here I am going to present the 5 phases of fasting as researched by George Cahill, one of the leading names in the field, and other scientists.
Phase I - The Initial Hours after Eating Cessation
- the primary source of energy in your body is glucose - which has been derived from your last meal
- glucose oxidation rate is 40 grams per hour
Phase II - 4 to 16 hours after Eating Cessation
- glucose oxidation rate is 7-8 grams per hour
- fat oxidation starts being upregulated
The body's primary fuel is still glucose. At this point the glucose from your last meal may have been completely used and your body starts using the glucose from your glycogen storage. Your body stores ~1,600 - 2,000 kcals worth of glucose as glycogen.
In this phase, your body upregulates the process of gluconeogenesis (GNG) - creation of new glucose from endogenous sources - so that it can provide glucose to the tissues that cannot survive without it.
- for GNG, glucose is made from muscle catabolism, recycled pyruvate and lactate, glycerol and other substrates.
Phase III - 16 to 32 hours after Eating Cessation
- gluconeogenesis (GNG) is progressively upregulated until the end of phase III
- glycogen stores (your glucose stored in muscles and liver) become depleted
Phases IV and V
- GNG decreases significantly
- at this point you oxidize glucose at a rate of 3.5 - 4 grams per hour
- you start efficiently using fatty acids and ketones (molecules derived from fat) for energy
- ketones become the main source of fuel for the brain
- muscle catabolism decreases significantly (since there is not much need for glucose)
Some Considerations
People doing water fasting for their first time may experience challenges in the first three phases. If they come from a background of eating multiple meals a day their bodies may be used to relying on glucose for energy production and much less on oxidizing fat.
Since you deprive your body of the energy source it's been used to, it is reasonable to think that negative symptoms may occur.
As glycogen is depleted and you run out of stored glucose, you may experience hunger, cravings for sugar and you may feel lethargic. This is your body urging you to eat.
As more time passes from your last meal, your body has to 'learn' to efficiently tap into your bodyfat for fuel.
I am assuming that the person fasting, the faster, is overall healthy and has no trouble adapting to the fasted state.
So, the duration of someone's fast is usually dependent on the amount of bodyfat they have.
For reference, I could fast for a few weeks - and I am lean. By direct extrapolation, overweight and obese subjects could do water fasting for weeks to months - such as in the cases of David Blaine and Angus Barbieri.
After 24 - 30 hours hunger fades away, as your body upregulates the oxidation of fat and ketones and downregulates the oxidation of glucose. GNG still occurs but at a lower rate - to provide the minimal supply of glucose to the tissues dependent on it.
In healthy people, the signal to end the fast happens when bodyfat becomes critically low and one cannot efficient use fat for fuel anymore. This is when hunger, the real one, surges strikingly.
This is usually the point of no return: you eat or die - as your body stops protecting your muscle mass - it starts upregulating catabolism in order to make glucose for fuel.
However, such critically low bodyfat levels are rarely seen today. For research, search for pictures of 'emaciated people' and you'll see what I mean.
Ending Thoughts
Fasting is not a mystical experience. It is an evolutionary mechanism that we rarely use today.
People going through 'blissful' moments in prolonged fasting are merely experiencing the effects of elevated ketones in the brain. The harsh science...
There are many possible benefits attributed to fasting which I will not go into here. People who undergo regular 3-10 day water fasts usually consume plenty of water and non-caloric beverages like black unsweetened coffee and green tea. Some take daily multivitamin pills.
I was a happy case with my 5 days fast. I was already habituated to higher fat and ketone oxidation, which is why I did not experience hunger and the symptoms of glucose withdrawal.
I think fasting is unpopular because there are no financial gains for someone telling you not to eat. Entities (people or companies) are interested in you being a consumer of something. This is one of the reason fasting and its potential benefits may be under the radar.
To become more educated on the science of fasting, go to an online scientific article database like Google Scholar or Pubmed and do your own research. I'd recommend verifying with multiple sources whatever claim/study you come across. And I also recommend applying critical thinking in your pursuit.
Disclaimer:
Please do not take this as medical advice. I am not a doctor and I don't play one either. Any actions you take, do it at your risk and under supervision.
To stay in touch, follow @cristi
Credits for Images: Jean Fortunet and Redrawn from Cahill (2006).
Cristi Vlad, Self-Experimenter and Author
@cristi: It would be interesting to see a post on essential nutrients. For example, if you made a cocktail that contains essential fatty acids, vitamins, and other micro nutrients - while having almost no caloric value.
I think this would allow for safer, and longer-lasting fasting periods.
Also, a quick question. I almost always hit a 'wall' about 36 hours in. Its not hunger per se, its more like an extreme lack of energy. I don't eat sugar/simple carbs, so my baseline glycogen levels should be a bit lower. I think whats happening is, I'm running out of glucose 36 hours in, and my body isn't used to ketosis.
Any ideas, recommendations?
I would assume your assumption may be correct.
You could try experimenting with nutritional ketosis to habituate your body to increased fatty acid and ketone oxidation. That would imply reducing carbohydrates (gradually, over the course of a couple of days) until you measure ketosis (either in urine or in blood). Spending some time in ketosis will make transition to extended fasting easier.
But 36 hours is pretty good! For health/maintenance purposes I think that's a good target. You don't have to be extreme. 36 hours once or twice a month should be sufficient to let your body increases the upregulation of the processes I mentioned above
I think such endeavors would fail: see the attempt made with Soylent.
It's easier to fast than to calorically restrict. We derive tremendous pleasure from eating. It's normal. It's a rewarding behavior to encourage our survival. Having a meal-mimicking concocting would not serve it's purpose.
Plus, when nutrients come from outside (when we eat), processes like autophagy (cell repair - renewal - cell self-eating basically) are reduced compared to fasting...
Safer, I don't know. If you purpose for safety, have a multivitamin when you fast and let your body do its thing... :)
@cristi
Nice brakedown. I would add that fasting in regular times (12 hour windows) can increase longetivity, energy and even correct metabolic syndrome. Our ancestors did not have food availuble all the time.
Fasting also can really cleanse the body from toxins since when food is no more the body uses up anything stored. Toxic material are used first. The goodies, like muscle and bone stay last.
that's a good poin @kyriacos.
Very well thought out and informative piece here! I had no idea about many of the facts you pointed out here, particularly the effects of elevated ketones in the brain.
One of the workout routines I was on a while back recommended intermittent fasting, supplemented by lots of liquids, protein shakes, etc. First just skipping out on 1 meal a day, then perhaps 1 day a week - all while doing a normal weights and cardio routine.
I didn't even last 2 days of skipping lunch. Maybe I should have started with just an entire day of fasting instead? Who knows. For me though, I just didn't like it.
If you supplement with protein shakes when IF you're doing nothing :)
Yes @team-leibniz elevated ketones in the brain may lead to a mild euphoric state - somewhat similar to the buzz from alcohol. I may go into the chemistry of it in a future post...
Cool Post
Steemon!
thanks!
Hi @cristi
Interesting post, I agree that men was programmed to fast for periods before feasting.
I also believe this thing of bottled water and expiry dates on food is also because people want us to buy more stuff. In the case of the feasting they did not have fridges to keep food, and also ate food that for us today would be off, they also drank water from rivers etc, without becoming ill. Perhaps you can also do an article on this.
of course! you're on point! and thank you for the suggestion. Our environment today is too clean, we lack beneficial microbes, which is why we may have more diseases of the immune system. We challenge our bodies too little..
I enjoyed reading this post and have always wanted to try fasting, I was surprised to read you had no ill effects in the gym on day 3 and 5. How was your recovery? For a first timer should they do it for 3 days and then build to 5. Last question , at the end of your fast is your first meal somethings light like soup so your stomach can handle it?
If I'd be doing this for the first time, I'd experiment with 16,18 or 20 hours of fasting for a few times. See how I feel and only afterwards I would progress toward prolonged fasting 24, 48, and then build from there.
As for the first meal, the break of the fast, I'd say it depends. Most recommend going easy. But I'd assume 3-5 days of fasting wouldn't not make your digestive system forgot how to it like it would do after 10+ days of fasting.
Personally, I broke my 5 days one with nuts, avocado, some dark chocolate, and some curd cheese as far as I remember...I wrote about this in my book Periodic Fasting. If you're really interested I'll take the excerpt and put it here
Great , or another post ^_^
Routine fasting makes you healthier no doubt.
well, that's what intermittent fasting is for. at the time of hitting the publish button for this post - I am 24 hours fasted...
Cool info! My boss does a quasi fast/cleanse once a year where I think all he ingests in water/lemon/honey for a week. I've always been curious about it.
sounds interesting, though I'm quite 'beware' of cleanses/detoxes and other fads. Fasting is fasting, water and mostly nothing else. :)
Thanks for the information. Fasting is something I have been thinking about trying again. I only did one multi-day fast and felt rather weak, but that was years ago so I want to try again.
You mentioned that you
I wonder if you could share a bit more on that. If you already wrote about that here, I may have missed it, so perhaps you could share a link. Thanks!
well yes, you can go and read my introduction post here.
But in short, I habituated myself to rely on fat through ketosis and the ketogenic diet - strict adherence.
Good post, and something people can consider.
Caution is definitely required.
I myself am thin, and don't overeat, so I would not want to do this for extended periods of time. I eat slowly and not large meals. So I don't fast, but sometimes a meal get's skipped once in a while to possibly, maybe, lol.. create the stress-factor of evolutionary benefits that you talk about.. in a small dose... lol
Yo're not promoting any fad diet or anything, but the whole "keytones" thing is a lot over-hyped recently. I just want to say that in case someone gets hooked on the mention of keytones and goes for the fad of a keytone diet.
Take care. Peace.
caution is utmost required!