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Let me introduce myself. My name is Mark Sisson. I’m 63 years young. I live and work in Malibu, California. In a past life I was a professional marathoner and triathlete. Now my life goal is to help 100 million people get healthy. I started this blog in 2006 to empower people to take full responsibility for their own health and enjoyment of life by investigating, discussing, and critically rethinking everything we’ve assumed to be true about health and wellness...

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February 22, 2017

Long Fasts: Worth the Risk?

By Mark Sisson
113 Comments

Inline_Long-Term_FastingIntermittent fasting, schmittermittent schmasting. The hot new trend is the extended fast—eating nothing and drinking only non-caloric beverages for no less than three days and often as many as 30-40 days. A mere compressed eating window this isn’t.

If fasting for more than three days sounds riskier than just skipping breakfast, you’re right. Long fasts can get you into trouble. They’re a big commitment. You shouldn’t just stumble into one because it sounds interesting or some guy on your Twitter feed wrote about it.

Skipping a meal or even an entire day of food makes evolutionary sense. We weren’t always successful on the hunt or with foraging. We couldn’t head down to the Trader Joe’s for shrink-wrapped steak, sacks of apples, and jars of honey. Reaching the fed state wasn’t a sure thing. Intermittent fasting—going out of your way to not eat, even though food is available—is a modern contrivance meant to replicate the ancestral metabolic environment.

But long fasts seem more evolutionarily aberrant. The evidence from extant hunter-gatherers, many of whom live on land far more impoverished and limited than our hunter-gatherer ancestors, indicates that outright famine is rare. The Hadza may not eat honey and wildebeest every day, but there’s usually plenty of something to eat.

Are there benefits to the longer fast, though? What’s the purported reasoning behind not eating for days on end?

The Logic of Long-Term Fasting

Weight loss

Back in the 1960s, obesity researchers were quite open to the notion that not eating for long periods of time could combat the results of overeating for long periods of time. The most famous case was of the Scotsman, an obese 27-year-old man clocking in at 456 pounds who, upon asking his doctor for help losing weight, was told to stop eating for a few days. He did it for a week, lost five pounds, and decided to continue the experiment for a total of 382 days. He didn’t do this willy-nilly. He took potassium, sodium, and various vitamins each day. He was under medical supervision for the duration, getting checkups each week.

It worked. After 382 days, he was 180 pounds, having lost 276 pounds. At the five-year checkup, he’d only regained 16. He might have been a bit stocky for the times, but by all accounts this long fast was a huge success. Most dieters nowadays eventually regain most or all of their lost weight.

In another study from the 1960s, 46 obese adults fasted for two weeks. No food, just water and vitamins.

On the good side, they all lost weight—an average of 17.2 pounds (from 7.7 to 31.9 pounds). At the two-year followup, half of them had either kept it all off or regained some of the weight they’d lost. The patients with diabetes enjoyed normal glucose levels throughout the fast and continued to have better glucose control after it had ended.

The bad news is that the other half regained every pound they’d lost or were so embarrassed at their progress that they failed to respond to the followup calls at the two-year mark.

Cancer

Cancer patients typically lose their appetite, and oncologists often prescribe anti-nausea meds to restore it. What if low appetite is adaptive?According to Valter Longo, a cancer researcher from USC, “normal cells” go into survival mode during starvation and display “extreme resistance to stresses” like chemotherapy. If this is the case, extended fasting could improve normal cells’ resistance to harsh cancer treatments. 

In one of Longo’s more recent studies, fasting for 3 days improved cancer patients’ resistance to chemotherapy. Leukocytes in those fasting for 48 hours before chemotherapy followed by another 24 after had less DNA damage than those who fasted for just 24 hours. saw less evidence of breaks in their leukocyte DNA. The result is preliminary but promising.

In an older case study (also authored by Longo), a woman with breast cancer underwent four rounds of chemo. The first round came during a six day fast. Other than dry mouth, fatigue, and hiccups, she felt well enough to continue working. For the second and third rounds of chemo, she didn’t fast. She felt awful the entire time, couldn’t work, and complained of severe nausea, fatigue, and pain. She decided to fast for the fourth and final round, which went as well as the first round. Fasting also improved her biomarkers, including white blood cell, platelet, and neutrophil counts.

There’s even a recent case study suggesting that fasting itself might combat cancer directly. In a woman with stage IIIa low-grade follicular lymphoma (non-Hodgkin’s), a 21-day water fast greatly reduced lymph size. She followed a plant-based whole foods diet immediately after, and by month 9 her lymph nodes were still of normal size.

If you’ve got cancer and are interested in long fasts, clear everything with your doctor first.

Immunity

In 2014, researchers used a 3-day fast to protect against damage to the immune system and induce total systemic regeneration of the immune system in mice. Fasting actually triggered the mice’s stem cells to begin production of new blood and immune cells.

A recent report on 6 autoimmune case studies sounds quite promising.

Case 1, rheumatoid arthritis: Symptoms included constant pain in all extremities, extreme fatigue, headaches, and occasional autoimmune conjunctivitis (pink eye). A month after stopping RA meds, the patient fasted for 17 days. Two days in, joint pain had subsided. A week in, all pain was gone and mobility was restored. Electrolytes were stable, and he maintained his progress at follow-up visits.

Case 2, mixed connective tissue disease: Symptoms included severe joint pain, chills, facial edema, weakness, fatigue, myalgia, photosensitivity, and tachycardia. She weaned herself off meds before fasting for 21 days. The first week was rough, but by day 10 she felt better. By 21 days, she had no complaints and remained off her meds. Electrolytes remained stable.

Case 3, fibromyalgia: Symptoms were pain, poor sleep, inability to sustain activity for more than an hour. A 24-day fast cleared them up. Electrolytes were stable.

Case 4, systemic lupus erythematosis: Symptoms were joint pain and skin rashes. Two weeks before the fast, she had weaned completely off her meds. On day 3, she was sleeping poorly and feeling nauseated, but on day 4 she began improving. Joint pain was gone. She cut the fast short after 7 days due to weakness and mild tachycardia, but that was enough—she remained symptom free at one year post-fast.

Cases 5 and 6, rheumatoid arthritis: 12- and 24-day respective fasts fixed symptoms for two patients with RA.

Hypertension

A 2001 study involving 174 patients with hypertension found that a 10-11 day water-only fast led to an average blood pressure reduction of 37 mm HG systolic and 13 mm HG diastolic. Those with severe hypertension (180+ mm HG/110+ mm HG) saw even bigger improvements—a 60/17 mm HG reduction on average.

You might have noticed that many of the cited studies were case studies of single individuals. While it’d be great to have RCTs with placebos and control groups and double-blinding, it’s hard and expensive to get a huge group of people together to fast for 21 days, monitor their vital signs, keep them honest, and ensure their safety. You couldn’t conduct a free-living long fasting study because you’d lose too many to McDonald’s-based attrition. You have to keep people in the facility. That takes a lot of money and manpower.

What Are the Risks?

Loss of lean mass

Any weight loss diet will lead to the loss of lean mass in addition to fat mass. The goal is to minimize the former and maximize the latter. Remember: when most people talk about weight loss, they really mean “fat loss.”

When a slightly overweight, otherwise healthy man drank only water for 44 days, he lost 25.5% of his body mass. A quarter to a third of the loss was body fat, the rest lean mass—mostly muscle.

Nutrient deficiencies

 Nothing’s coming in. You’re going to run out of stuff.

  • In the 44-day fasting study, the subject also developed deficiencies in thiamine, riboflavin, and vitamin K.
  • A man with non-Hodgkin’s lymphoma fasted for 53 days (he intended 60 days, but couldn’t make it) and ended up with a dangerous neurological condition called Wernicke encephalopathy caused by severe thiamine deficiency. 
  • A woman admitted herself to the hospital after a 40-day water-only fast. She had severe sodium deficiency upon admittance and developed severe deficiencies in magnesium, phosphorus, and potassium upon eating.

Refeeding syndrome

Nutrient requirements drop during a fast. Your body isn’t doing nearly as much as it does when you’re fed, so you can get away with less. Serum levels of basic minerals like magnesium, potassium, and phosphorus remain normal, while intracellular levels drop. But upon refeeding, the situation reverses. Your insulin spikes in response to incoming food. You’re suddenly having to store fat, make and store glycogen, and conduct various other metabolic processes that increase intracellular nutrient requirements. To meet the need, electrolytes move from serum to cells, creating a deficiency on the serum level that can be quite dangerous.

Increased susceptibility to infections

A study in famine victims found that starvation increased susceptibility to infections, particularly malaria. Sometimes the infections were suppressed during the fast and only manifested upon refeeding. Fasting isn’t famine, but it’s similar enough that we should heed the story.                 

Tips for doing it safely…

Drink green tea during the fast. Purists will scoff at you for ingesting anything but water. Forget them. A 2003 rat study found that green tea protects against the fasting-induced damage to the intestinal lining during a 3-day fast. Remember: these were rat days. In human days, those 3 days are more like 90.

Take MCTs. Tim Ferriss recommends taking medium chain triglyceride oil in the first couple days as a tool to ease your way into a long fast. If you’re already on a ketogenic diet or count yourself as a fat-burning beast with robust fat-burning mitochondria, you can probably skip this.

Take magnesium, calcium, potassium, and sodium. Long fasts seriously perturb electrolyte homeostasis. I vastly prefer getting my electrolytes through a tall glass of Gerolsteiner mineral water (magnesium and calcium) spiked with sea salt (sodium) and lime juice (potassium).

Take thiamine/B-complex. Many studies indicate that fasting depletes thiamine and other vitamins, so stay on top of that. The Scotsman I discussed earlier took a nutritional yeast tab each day, probably for the B vitamin content.

Take vitamin K. A week of fasting depletes vitamin K, which is incredibly problematic if you’re fasting before major surgery. It’s also not great for general health.

Make mineral bone broth. With all the fat strained out, bone broth is quite low in calories and will have a negligible impact on your fast. Throw in a big handful of leafy greens with the stems. I like collards and beet greens, personally. You can either remove the veggies (all the minerals will have gone into the broth) or eat them.

Refeed with a light, low-carb meal. Don’t come off a week-long fast and immediately tuck into a platter of ribs. Don’t refeed with high-carbs. Large meals are difficult to handle after a long fast, and high-carb meals may lead to dangerous levels of fluid retention.

Take two or three days to ease yourself back into your normal routine. Eat smaller, lighter meals. Don’t train too hard. Refeeding syndrome is a real threat.

Have a good reason for doing it. Long fasts are serious, and you should have a serious reason for embarking on one.

Obese? Sure, a long fast with medical supervision and electrolyte and vitamin supplements can work.

Got non-Hodgkin’s lymphoma? If your doctor is on board, a 10-15 day fast might really improve survivability.

Got rheumatoid arthritis or some other autoimmune disease that just doesn’t respond to anything you’ve tried? Maybe a week-long fast will help.

Got invited to a silent meditation/fasting retreat? Go for it.

Does your spiritual practice or religion call for a four day fast? If your faith is important to you and completing this fast is integral to it, you should fast.

But:

If you’re trying to reveal the bottom half of the six-pack you just know is lurking beneath your gut, long fasting is not the answer.

If you’re hoping to shed the last of your baby weight, don’t try a long fast.

If you’re sleeping five hours a night, working twelve hour days, and walk around a frazzled ball of stress, don’t not eat for a week straight.

If you’re fairly healthy and happy and everything’s going well, I’m not sure. Don’t make it a habit. Treat it like a marathon, maybe. A once in a blue moon event you pursue purely for the novelty.

By now, you should have a better grasp of the potential benefits and drawbacks of long fasts. They’re not for everyone or every situation—and I think shorter fasts or compressed eating windows make more sense for most people—but the long fast is an intriguing option that can be safely done if you take the right precautions.

Do you think you’ll try one? Have you tried one? How’d it go?

Let’s hear from you down below. Thanks for reading, everyone.

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113 Comments on "Long Fasts: Worth the Risk?"

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Monikat
Monikat
7 months 1 day ago
This is a great post and something I’ve been interested in for a long time. A few years back I attended a lecture on avoiding cancer, and the doctor discussed something like the research you mention above. He said it something like this: Imagine a neighborhood filled with normals and one party-er. The normals go about doing their business, doing their job. The party-er, on the other hand, just throws nons-top parties; every time you look the limo is pulling up… Then imagine a huge recession hits the area. If you look at the neighborhood a year later, things have… Read more »
bigmyc
bigmyc
6 months 11 hours ago

If that has more than a shred of true parallel with fasting vs. cancer, it would be a wonderful thing. Since going Paleo, I have been aware that fasting is a powerful tool to employ vs. cancer and general disease and in theory, it seems like it would be.

Nic Anderson
Nic Anderson
7 months 1 day ago

What are thoughts on taking BCAA while under long term fasting to help maintain lean muscle mass?

Joe
Joe
7 months 1 day ago

yes i second this question ! As a late 40’s male, i’m always concerned with maintaining my muscle mass, and i’m concerned that doing even a 2-3 day fast will cause a measurable loss of some muscle mass, and i’m not sure how re-attainable that muscle mass is at my age….

Meg
Meg
7 months 1 day ago
You can fast any way you want, but taking enough amino acids can stop autophagy, which is where the magic happens. Your body will burn through glycogen for the first 3 or so days, then it will start metabolizing excess body fat. Autophagy kicks in and as the body shrinks, your body will selectively break down unneeded blood vessels and extra skin, skin tags, and whatever isn’t necessary for survival. It really only goes after lean muscle mass once all the fat stores are completely gone. See The Complete Book of Fasting by Dr. Jason Fung and Jimmy Moore for… Read more »
2Rae
2Rae
7 months 1 day ago

Thanks Meg, good to know! I have a few skin tags and “extra” fat…..
I will look for the book.

BobM
BobM
6 months 30 days ago
Skin tags are possibly caused by insulin resistance. Fasting will also help lessen your insulin resistance. For me, a low carb diet helped lessen the number of skin tags I was getting, but intermittent fasting (up to 5.5 days) cured those. I now have very few skin tags, and the ones I do have are small. When I fast longer than 1 day, I still drink coffee with a small amount of cream, I drink a Gerolsteiner, and I have bone broth/stock with salt and “no-salt” (potassium chloride). I drink these daily. I also do what it takes to make… Read more »
Tee Dee
Tee Dee
6 months 3 days ago

I’ve just finished reading Dr. Jason Fung’s book on fasting and it’s fantastic–glad you mentioned it, Meg..

Elizabeth Resnick
7 months 1 day ago

It all seems to come back to something very simple…listen to your body. When cancer patients don’t have an appetite, respect that instead of forcing food (which is usually starchy junk anyway). Personally, while I wouldn’t mind experimenting a little bit with IF, I can’t imagine going a long stretch of time without food. I’m very active and really enjoy my food! But if I had some major health challenges I would consider it. And the case studies are pretty compelling.

wildgrok
wildgrok
7 months 1 day ago

My exact take on this 🙂

“But if I had some major health challenges I would consider it. And the case studies are pretty compelling”

nic
nic
7 months 1 day ago
Join the I recently fasted 35 days on water, herbal tea and herbal broth, mainly to reach autophagy to heal my breast cancer Tumor. Unfortunately it hasn’t worked. The Tumor is still there. Maybe the fast was not Long enough ? I lost a total of 12 Kilos of which I regained 8 within two months. However, spiritually the fast was an amazing experience and after the inital 3-4 days I felt great the whole time. I broke my foot a couple of years ago and the nerves never really healed, I had numb parts on top of my foot.… Read more »
Time Traveler
Time Traveler
7 months 21 hours ago

I agree. When an animal in the wild falls ill (or when a lion gets bit by venomous snake), it retreats to a secluded place and refrain from eating and drinking, until it get better. Instead of burdening the body with digestion that pulls scarce resources, it best to let it be.

chibi pink
6 months 30 days ago

Except that cancer patients don’t have an appetite after a dose of chemo. For me there was 5 days of fasting after every dose and that was with the meds. To add a day of fasting before that would have been unnecessary torture. The nausea meds are really given to stop vomiting, not prevent fasting. In the old days chemo chairs always had a bucket attached and the whole scene was a barf-a-rama. But, as I’ve written in my blog, we all need a bit of voodoo when dealing with cancer, so if it doesn’t hurt, it might help. https://girlvstamoxifen.wordpress.com/2017/01/24/a-bit-of-voodoo/

Pedro Toledo
Pedro Toledo
7 months 1 day ago
Great post! I’m in the middle of my third week-long fast. I do it every six months to a year. It is an awsome experience to know yourself, to get to know you really do not need the food to live and be productive. I’m already health and on my weight, but still I lose a little fat and look awesome after the fast! I really enjoyed reading this post. Most important recomendation, if you fell bad in any way, just eat! Second most importante recomendation, always have some broth on the fridge, going to bed with a warm belly… Read more »
gho
gho
7 months 1 day ago

thanks for the post! very timely for me, as i’m planning to do my first week-long fast in a few days. i’ve eaten in a smallish time-window (~10-5) during the week for a few weeks, and i’ve been psyching myself up for the weeklong fast. i’ve prepared plenty of bone broth for the next few weeks, as well.

any tips / suggestions for a first-timer?

thanks in advance!

Mike H
Mike H
6 months 30 days ago

Close family member has cancer and is advised by the doctor to do long term fasts. I do them with that person as moral support. Google Tim Ferris’ method or check it out in one of his books. In short, MCT powder, KetoCaNa, salt/lime in water and then after day 2 or 3 go to only mineral water. After the 2nd time fasting I could go straight to mineral water and have no problems. When I exercise, i do a gram or so of BCAA in accordance with Tim Ferris, but on days off it’s only water.

Libby Mason
Libby Mason
4 months 15 days ago

Exactly what I’ve been doing for the past 6 days, sipping on some home made broth just before falling asleep.
Do you end your fasts because you are hungry and need to eat or because you reached your target?

Hap
Hap
7 months 1 day ago
I can’t imaging that a three day fast is problematic except in certain situations. Fasting with fluids gets the job done. Remember Pareto…..even 20% gets 80% benefit. Journal of Translational Medicine just published Dr Valter research in humans on fast mimicking diet. Good results in improving certain biomarkers. Frankly, this has probably too many financial overtones since he has spun off a company that patented the diet. However, for specific medical purposes (like prechemotherapy?), has merit. the rest of us can inexpensively water or tea /coffee fast 24/36 hours.
Rick
Rick
7 months 1 day ago

I have done a 5 day fast and a 4 day. Both were very manageable and helped stabilize my Blood Glucose. I can say I studied Dr Jason Fung prior to fasting long term and I also regularly eat once a day which helps. The best benefit to me was the mental aspect. I realized most “hunger” is in my head and routines vs belly.

HealthyHombre
HealthyHombre
7 months 1 day ago

“If you’re trying to reveal the bottom half of the six-pack you just know is lurking beneath your gut, long fasting is not the answer.”

OK … well … nevermind then.

Kyle
Kyle
7 months 1 day ago
I followed the exact prescribed process outlined in Tim Ferriss’ book, Tools of Titans. Essentially, he recommends a three day fast with tons of water spiked with lemon and sea salt along with up to four table spoons per day of MCT or coconut oil. Coffee and tea are also fine. Along with that he suggests 2-4 hour of brisk walking on day one (and two if you want/need it). No weight or HIIT training on these three days! The whole point of this three day process is to kick your metabolism into ketosis quickly, and then maintain that state… Read more »
Joe
Joe
7 months 1 day ago

thx for sharing the Tim Ferriss info, Kyle…he is very knowledgeable. When u fasted 3 days, did u lose any fat and/or muscle mass ? What was your body composition like when you entered the fast ? My only concern for myself, if i do a 2-3 day fast, is losing muscle mass and then not being able post-fast to regain that mass, since I’m in my late 40’s. Maintaining muscle mass as you age is super important.

Kyle
Kyle
7 months 1 day ago
I didn’t do any type of body comp test to have real numbers. I did not lose any muscle mass from what I can tell. In fact, I’d argue it’s unlikely to do so in such a short period of time. Re: body fat…hard to say. I definitely looked a lot better but that could be a symptom of water retention. The point in the three day period is not to necessarily lose body mass (fat or otherwise) but to instead get yourself to an optimal metabolism (keto in this case) in order to burn more fat. I quickly went… Read more »
Tee Dee
Tee Dee
6 months 3 days ago

Actual muscle loss would be the very last thing to happen, as someone mentioned before. Your metabolism changes to a more protective mode during a fast if anything. You’d lose fat and dead cells and other waste well before any muscle loss. We wouldn’t be here if we evolved to lose muscle during a period with no food. That’s the reason humans store fat in the first place, to get them through a time with no food. But muscle is actually protected.

gho
gho
7 months 1 day ago

thanks for that reference to the book! i have it on my desk but have yet to start reading. 🙁 looks like i have some homework for tomorrow.

Eric
7 months 1 day ago

How does a person deal with diarrhea when coming off a fast? I often have diarrhea for the 1st day when starting to refeed. Post fasting diarrhea seems to be a pretty common issue on some internet boards. I have yet to find an explanation or a solution. Suggestions?

Margaret
Margaret
7 months 1 day ago

Mark–For the autoimmune case reports, you failed to mention that the patients preceded and followed the fast with a vegan diet, and that the authors conclude the paper by saying a vegan diet appears to be necessary to sustain the results.

shasha
shasha
7 months 1 day ago
Tried a long fast of three weeks once. Back in my 20’s, all unfiltered apple juice….at the time I wasn’t working and had little stress in my life. Later realized that was way too much sugar!l I think I ended up with a blood sugar imbalance as I almost passed out (but was quickly revived by eating a prune.) That ended it and I haven’t done a long one since but did try a 3 day fast on green tea and water a few years ago and didn’t notice any apparent ill effects. I would like to try a short… Read more »
bill
7 months 1 day ago

Let’s see, you’re ingesting tea, MCT oil,
magnesium, calcium, salt and lime juice,
yeast, vitamin K, and bone broth and
vegetables. Sounds like what’s called
“eating” to me.

Ridiculous fad, promoted by charlatans…

Time Traveler
Time Traveler
7 months 21 hours ago

+1

Mark
Mark
7 months 16 hours ago

You think that criticism is not addressed by advocates?

BobM
BobM
6 months 30 days ago

hmmm…That fad has helped me lose another 25 pounds (after losing an initial 30 using low carb). It’s also lowered my blood pressure at least 15 points (systolic), reduced my insulin resistance and blood sugar, asthma, allergies (went from gobbling multiple pills per day to one per YEAR), GERD, overactive bladder, skin tags…too many to list. I stick more towards coffee with small amount of cream, water, some minerals, bone broth.

Ned Mills
Ned Mills
7 months 1 day ago

I occasionally do a fast for 24 hours. For an appetite suppressant, I drink ginger tea made from boiling chopped ginger root. Do any of you have suggestions for other appetite suppressants?

Will Wilkin
7 months 1 day ago

I’ve been doing 36-hr fasts about every 7 – 10 days and feel GREAT! That includes during the fast. For me, no appetite suppressant is needed or even wanted, it feels GOOD to fast sometimes. But I believe I am usually or always in ketosis to start with as I follow a very low-carb, high-fat diet. In fact, every morning I wait until at least 12 hours after yesterday’s last food before I eat. Being in a fat-based metabolism rather than glucose-based metabolism is a natural appetite suppressant.

Dee
Dee
7 months 1 day ago

Apart from staying well hydrated, coffee is a good appetite suppressant. It’s touted as such, and works well in my experience too, often delaying hunger for a few hours. Not sure if decaf has same effect, but if caffeine is not an issue….I’ll try your ginger tea next time too, sounds great. 🙂

Monica
Monica
6 months 10 days ago

When on a LC diet, hunger usually lasts seconds to minutes. When hunger hits me harder (days 3-5 of the fast) I add butter to my coffee. Going to sleep works, too.

Shary
Shary
7 months 1 day ago
Personally, I think long-term fasts of anything more than a week (and even that’s too much for some) are a really lame idea. In starvation mode (long-term fasting), the body will literally cannibalize itself in an effort to stay alive. That doesn’t sound like a worthwhile ambition if you value your health. Other nasty things can happen as well. Years ago I read about someone who fasted as a protest. After several weeks he lost his eyesight. It didn’t come back. He also lost the ability to eat and derive nutrition from food–even when he desperately wanted to. I guess… Read more »
Tee Dee
Tee Dee
6 months 3 days ago

Shary, that old myth about the body canabalizing itself has been thoroughly debunked for decades, actually. If you go to Intensive Dietary Management and read Jason Fung’s remarks on this, you’ll see it explained extremely well. The only ones who want us to believe that we’ll waste away from fasting is Big Food and Big Pharma.

Oesi
Oesi
8 days 16 hours ago

And if you check the reference with the person who fasted for 44 days and lost of his muscle mass, you will see that it was David Blaine. He locked him self up in a small box for 44 days und just drank water. But this also means, that he didn’t move. And if you don’t move, you lose your muscles no matter how much you eat. Happens to everyone, who had an accident and had to stay in hospital for some time.

Tee Dee
Tee Dee
6 days 20 hours ago
And then there was the Scottish man who fasted for 382 days and came out of it quite well, indeed. Blaine’s inactivity certainly didn’t do him any favours. Just standing up and puttering around one’s house is better exercise than he got. They didn’t do any good tests like a dexa scan afterward; just the old, inaccurate pinch test and muscle loss was determined by creatinine excretion, so it’s not the best example for me to use. There are very inactive elderly people who maintain more muscle when they take in more protein than they had previously consumed, so we… Read more »
James
James
7 months 1 day ago

I had a good experience on my one 3-day fast. Most critical was staying well hydrated, electrolyzed, and rested–no strenuous or tiring activity of any kind.

One additional benefit I might add to this list: giving the GI a little break and a gentle “cleaning”. Maybe TMI, but what I found fascinating was that after days of no food, substantial bowel movements persisted.

Eric S.
Eric S.
7 months 1 day ago

It would be interesting to take a strong probiotic during the fast to see if the “cleansing” was enhanced. The one I am currently taking had me in the bathroom 6 times in a single night (next morning I was almost 3 pounds lighter than the previous morning lol).

Not sure if it matters but I was recovering from anti-biotics and switched from SAD to Keto after finishing the anti-biotics. My first time on Keto and it is amazing.

Aloma Yiannett
Aloma Yiannett
7 months 1 day ago

Thanks for this post it was exactly what I was looking into, I want to implement short fasts into my personal prayer life and am also on a strict workout and nutrition regime for health and weight loss and didn’t want to interfere with it, it’s good to read there are ways to do it carefully that won’t disrupt ur regime but also can have benefits health wise not to mention the clarity u gain spiritually from denying urself. Thanks again!

Tom White
7 months 1 day ago
I’ve been eating primal for 5+ years and decided to try my first fast a few months ago. Just a n=1 experiment. I had no predetermined length of fast – I just winged it. I drank only water and some cold tea and took my daily vitamins. After 10.5 says I stopped the fast because I was concerned about the health of my gut biome. After gradually returning to eating I had issues with solid waste frequency and lack of firmness. Most of my bacterial enzymes are from Greek yogurt and aged cheese. This was not enough to return me… Read more »
Bryan
Bryan
7 months 1 day ago
Mark, thanks again for another expert blog. I’m 57 year old male, pretty strict paleo to keto, healthy, work out a lot, about 15-20 lbs overweight versus my adult weight goal, and am already incorporating 24-40 hour intermittent fasts into it once or twice weekly with only bone broth/water/coffee during fasts. Read Jimmy Moore’s fasting book – good info, but longer fasts pretty radical. My only desires on fasting are to add it into the mix to mildly shock/challenge my system, definitely be in ketosis during fasts, and increase body fat loss a little beyond paleo/keto. Your post confirmed my… Read more »
Rory Mulhern
Rory Mulhern
7 months 1 day ago

What is considered a long fast. My usual is 36-45ish, that still be considered short?

Rob Hanna
7 months 1 day ago
If you’re seeking the answer regarding fasting as the ancient practice of convalescing on water alone (or dry fasting) for therapeutic intentions, then historically a long fast is 40 days or more. This is based on the thousand years practice of fasting as a proven health injunction. If you are asking in regards to the current fads of caloric restriction, intermittent fasting, and subsisting on broths and teas as dietary modification options (these are not fasting, but something else entirely different) as regards a search for other positive physiological and emotional consequences due to such practices, I couldn’t say… might… Read more »
CJ Hayes
7 months 1 day ago
I did a 40 day fast with broths and some juiced fruits and vegetables plus some added medicinal protein at my doctor’s recommendation. I can honestly say I had more energy during the fasting period than I did before. I followed it with clean eating afterward and lost a lot of weight and felt excellent. Unfortunately, i went back to my old way of eating and gained it all back plus. In October of 2017, I discovered Paleo and Primal living and my wife and I have embraced it full on. Did my first sprint today as part of the… Read more »
serito
serito
7 months 1 day ago

Oct 2017? The big news is you are from the future! In our timeline it is february 2017.

Eric S.
Eric S.
7 months 1 day ago

2017? Sigh… not again…

CJ Hayes
7 months 18 hours ago

OOps!! I meant Oct. 2016

Bob Niland
7 months 1 day ago

What’s the impact of extended fasting on gut flora (the microbiome)? Those lifeforms are obviously going to be stressed, perhaps to net benefit, but that would be conjecture.

And if there are hazards there, could they be mitigated by supplementing with probiotics and daily non-caloric prebiotic fiber to keep the critters happy?

Rob Hanna
7 months 1 day ago
This is a great question. I’ve been wanting to take gut cultures prior to, during and after a long fast to get them tested by UBiome or some such service, to see if there was any delta… but I was too cheap about forking over the dough to buy the multiple testing packages and missed my opportunity recently when I did a 21 day fast… sigh, oh well. It was more of a curiosity impulse of a theorist than an actionable necessity for a practitioner. My sense from the literature I’ve read so far is that the microflora and fauna… Read more »
Rob Hanna
7 months 1 day ago
Unfortunately, even though I’ve a good deal of respect for Mark’s work, I’m compelled to share that this post is NOT good information about fasting. This may perhaps be for several reasons, but the most visceral is the wildly misleading and very common conflation that many believe regarding fasting as starvation–these two conditions are NOWHERE near the same thing. The fallacy is like comparing bicycles to military nuclear rockets and saying they’re both are dangerous because they move, but in reality one is highly useful and common to the masses and the other is not, unless there’s been a big… Read more »
Shary
Shary
7 months 1 day ago
So…at what point does fasting become starvation, Rob? Saying there’s a big difference between intentional fasting versus famine is playing games with semantics since the end result is essentially the same if carried on long enough. I would think an obese person has enough bodily reserves to fast for a long time, whereas a fairly thin person might be on the ropes rather quickly. I routinely fast between 6 p.m. and 11 a.m. or noon the next day. For me this means nothing at all after dinner (other than water) and a single cup of tea in the morning. I… Read more »
Tess
Tess
7 months 1 day ago

Also, FWIW I just wanted to add to the “contraindicated for pregnant and nursing women” sentence that it appears most religions that fast (ie Ramadan) contraindicate menstruating women… This raises questions regarding women of childbearing age fasting for longer than say 28 days (I’d like to hear Mark’s opinion regarding this 🙂

Rob Hanna
7 months 1 day ago
In both sexes, it is not uncommon for hormonal levels related to sexual reproduction (e.g. testosterone and estrogen) to become reduced during long fasts (i.e. 40 days or more). As well, many religions contraindicate women participating in ritual practices for a variety of reasons. Especially menstruating women… Regardless your faith, you can rest assured from a health and wellness practitioner standpoint that menstruation is not a contraindicating factor for women seeking to fast for longer than 28 days (i.e. or any menstruation cycle period). As to fertility increasing or decreasing during long fasts, that’s another question… but after any long… Read more »
Tess
Tess
6 months 30 days ago

Thanks for taking the time to reply Rob. Your point
“And this is due not just to the deep and comprehensive cellular autophagy, but also the complete and holistic rest that attends a properly conducted, therapeutic fast.” is something I hadn’t considered before … fasting being a way to give the body rest and a deep clean, I’ll have to ponder this some more 🙂

Grant
Grant
7 months 17 hours ago

In no way, shape, or form is intermittent fasting a fad. It’s a healthy, sustainable way to live.

I also, don’t understand the rest of your post. You seem to be agreeing with Mark.

Tee Dee
Tee Dee
6 months 3 days ago
Thanks for that, Rob. I’m also very tired of click-bait headlines and comments in the area of fasting. But the other sentence that’s been said to death is: “Most dieters nowadays eventually regain most or all of their lost weight.” I enjoy this site and have learned quite a lot, but when I read that sentence, yet again, I felt a little deflated. That remark has caused more people to wonder, “why bother?” than any other I can think of for those needing to lose weight for health reasons. At the very least, it should explain that only those who… Read more »
Velerie Hall
7 months 1 day ago

I faced similar problems a few months back as because of my daily schedule, I was not able to eat properly which impacted on my health.
Thanks for sharing the tips for doing it safely.

Lisa
Lisa
7 months 1 day ago

I dry fast once a week for 24-40 hours. I am fighting a rare, progressive muscle disease. I have tried autoimmune and Paleo diets with no luck for the past 5 years. I’ve been eating raw as well. I feel fantastic after a long fast. I totally feel rejuvenated! I am presently on a personal herbal protocol to protect my kidneys and the rest of my body. I understand that while being dry the cells will squeeze the interstitial fluids out to hydrate and take some bad cells with it.

Time Traveler
Time Traveler
7 months 21 hours ago

Hi Lisa, I’m glad it’s working for you. As I’ve mentioned above, I came across several websites that cover eating raw meat (I’m sure you know which one) and was very impressed with the info. I wish I could make the switch….

david
7 months 1 day ago
I lost 100 pounds last year from a long term low I couldn’t break with KETO using long fasts. (In fact my thyroid went hypo by TSH over the year I did KETO and went back to normal with fasting.) I mainly used 5-7 day fasts. I didn’t really even watch what I ate when not fasting to a great extent more than just generally being aware. The 1960’s study sounds bad but 50% having measurable long term improvement after a single 10 day fast is quite remarkable given the figures being bandied about for diet failure exceeding 90%. (I… Read more »
JTB
JTB
4 months 28 days ago
David, were/are these water-only fasts, and how often were/are you doing them? Did you take supplements of any kind? I’ve done a couple water-only fasts recently but only lasted 2 to 3 days each time (I was aiming for 4). Actually, it’s not accurate to say water-only; I was having a cup of coffee in the morning and green tea (straight up loose leaf, no flavorings or additives) in the afternoon. I’ve read (from Dr. Jason Fung, mentioned elsewhere in this comment thread) that even small amounts of protein can break the “fasted” state and stop autophagy so I was… Read more »
david
4 months 5 days ago

Mix of water only and some calling sub 500 calorie a day fasts. Over 5 days I do water lite salt multivitamin, also camu-camu powder (basically vitamin c).

It’s gotten so much easier I basically almost don’t believe it. I can be somewhat full for a couple days now. Makes starting a fast really easy since first couple days were the hardest. Biggest enemy mainly boredom now.

JTB
JTB
3 months 13 days ago

Thanks so much for that info, and congrats on coming up with something that works so well for you and sticking with it. Boredom and habit were really, really tough for me during the fasts I did (1 at the beginning of March and 1 at the beginning of April).

Breaking the routine/habit and finding a new way to cope with stress and boredom seems to be a lot harder than the actual not eating, which was kind of a surprising thing to learn. Your experience is so inspiring — thank you for sharing those details.

JenK
JenK
7 months 1 day ago
Thanks for the great post Mark, it’s just what I wanted to read about today. I’ve been researching this topic for a few weeks now on Dr. Jason Fung’s website. I’ve started doing a 42 hour fast one or two days a week, to reverse insulin resistance and gain more insulin sensitivity, to reap the metabolic benefits of up-regulating/down-regulating this or that process, and to burn off any risky fat that may be lurking around my liver and pancreas. I’ve followed the PB for the last five years, and strict LCHF/keto since December, but when I did the fasts I… Read more »
Jen
Jen
7 months 1 day ago

Anyone interested in fasting should read Dr. Jason Fung’s Complete Guide to Fasting. It goes into detail about topics in this blog article and corrects a few things written above. It’s an awesome book.

Jordan Hodges
Jordan Hodges
7 months 1 day ago
This is great! Interestingly, I am at the end of my first water fast (supplemented with a carefully chosen multivitamin). I feel great, but I have decided to start the refeeding process tonight after 5 days just because I am not an experienced faster and feel that I am already pushing the envelope. After a ton of reading and research, I decided it would be something good to try. I did not do it for weight loss (but did lose about 5 pounds), but because I was interested in some of the proposed health benefits – namely because it is… Read more »
Tess
Tess
7 months 1 day ago
One thing worth considering with longer fasts is the effect (or possible effect) on mood/personality… I saw Rachel Hunter (on her tv series Tour of Beauty) do a week or 2 fast and she admitted that she got very angry/aggressive/ easily annoyed etc… However she wasn’t primal/paleo to begin with so maybe someone who is already a fat-burning-beast wouldn’t have such side effects, and it was a “TV Series” so I’m not sure how much faith we can put in that, but she did seem genuinely irritable (maybe try meditation, yoga etc when doing longer faster for your family’s sake… Read more »
Vincent Beretta
7 months 1 day ago

Hi Mark, I’ve been on the mend after an impact injury to my knee (fell playing pond hockey in jeans ie no protection) and I am getting back to the gym and have heard a lot lately about simply fasting for a day a week every week and I am intrigued about a longer fast. My Question is about the use of green tea Kombucha during an extended fast – would this be something you recommend as I have been using it for a while now and love it…?

Kurt
Kurt
7 months 1 day ago

At age 57 I’ve done many 3 day fast about once every 3 weeks. I usually do 2 hours of aerobic exercise (biking/jogging/hiking) and one hour of weight lifting during those 3 days. I follow a Primal diet before and after with good protein sources and I have not noticed any problems with strength, endurance or muscle loss.

Cheryl
Cheryl
7 months 1 day ago

I did a 9 day water fast but I had so much pain in my lower back I had to stop. I wondered if the pain was caused by a deficiency of some sort. But they said it’s retracing but I don’t buy that to this day. The thought of reliving that pain keeps me from trying another fast. It helped my SIBO so much though, I really want to do another.

JenK
JenK
7 months 1 day ago

Hi Mark, thanks for this interesting and thought-provoking post. My question is, what impact does fasting, for any length of time, have on gut flora. It seems to be positive, given all the benefits, but what exactly is going on in there when we deprive the critters of their food?

csrollyson
7 months 1 day ago
@Mark, thanks for this post; I’m sharing widely. I’ve done a couple 36-hour fasts when I’ve been sick, so I want to encourage you all to try this (same idea as the cancer), and I think it hastens my recovery. I only drink green tea and water when I fast. When I get the flu or a bad virus, I starve it until I start feeling better. If I had a serious illness, I’d totally do longer fasts and will probably try longer ones just for fun. I IF often and find that hunger is oft driven by habit rather… Read more »
Jacob
Jacob
7 months 23 hours ago
I had a dexa scan a few months ago and discovered that instead of the 16% body fat the machines at the gym told me I had it was 21%. I ditched most alcohol ( glass of wine once it twice a week ). Dialled down my carbs whilst increasing the amount of vegetables. I have been on a 23 hour fast every other day ( meaning just one meal before bed then two meals the following day then just dinner the day after and so on ). I have a lot of muscle mass ( 95 percentile of guys… Read more »
Rob
Rob
7 months 21 hours ago

After doing two 24hr fasts a week for some time, my friend and I decided to try for 72hrs. Strangely at some point the feeling of hunger went away… but then I started actually dreaming about food. Not sure if I didn’t drink enough water or what but the only negative effect I had was a killer headache on the third day.

Time Traveler
Time Traveler
7 months 21 hours ago
And then there are those who resort to eating meat only (from head to tail organs included) and drink water, who do dry fast with ill effect. This stem from the idea that hunter gatherers in the true sense and prior to the agriculture revolution, weren’t always successful in their hunt and sometime didn’t eat for days. There are several websites on the subject and I find their experience and results vis.a.vis dealing with health issues fascinating. I seriously thought about trying it out as a way to deal with autoimmune disease, if not for the fact the Meat is… Read more »
Tee Dee
Tee Dee
6 months 3 days ago

I know the site you’re referring to with the raw meat diet and dry fasting. I’m not quite ready for that, yet, but it’s very insightful. Have you considered giving blood/plasma for high iron levels? Sometimes women in menopause develop this and find that giving blood can help.

Time Traveler
Time Traveler
6 months 3 days ago

Thanks for your comment. I gave it a shot for a few days and it wasn’t bad but an all meat diet isn’t for me. I would love to give blood but I am also slightly anemic and it all stems from a g6pd enzyme deficiency (look it up). I is frustrating and depressing as it has ntoing to do with how wel I eat, sleep or workout. 🙁

Tee Dee
Tee Dee
6 months 3 days ago

I’m sorry to hear that; it does sound very frustrating.

BlackBird
BlackBird
7 months 21 hours ago
I just wanted to share the effect of my 6 day water and green tea only fast. I had been having some allergy/autoimmune issues for months resulting in a constant sniffly nose and sneezing. Also I had eczema on my arms. After a few days my sinus problems went away and the skin on my arms was a lot better. My sinus problems are only now creeping back, despite being on a low inflammatory diet for months. (Obviously I’m consuming something which my body doesnt agree with but I havent been able to eliminate it yet) Its not really a… Read more »
Time Traveler
Time Traveler
7 months 21 hours ago

correction: who do dry fast with “no” ill effect

Reluctantexan
Reluctantexan
7 months 18 hours ago
I started following the Fung Protocol in 2015 after eating LC since 1972. The reason was that I had not lost fat for 6 years and wanted to shake things up. IF allowed me to break that plateau. At age 72 I walk 2 miles every morning before dawn, take no prescription meds and have no illness other than recurring facial dermatitis which doctors can’t diagnose. I’ve begun taking foods out of my diet and have it successfully controlled. Taking out cow’s milk dairy got me losing fat again, and that was a total surprise. My IF usually consisted of… Read more »
Tee Dee
Tee Dee
6 months 3 days ago

That’s so inspiring, Reluctantexan. I’m 60 now and it can get so discouraging reading about ‘all the things that slow down’ and the ‘sleep problems’, weight gain etc, if I’m not careful about what I read these days. I eat one low carb meal per day at 1pm and it’s much easier than I thought it would be. I’d like to work my way up to 48 hours and then maybe 72 once in a while..Thanks for sharing your experience–all the best!

Starmice
Starmice
7 months 18 hours ago

I’ve been interesting in trying fasts after listening to Dom D’Agostino’s podcasts on ketosis. He theorizes that a 5 day fast 3x a year could eliminate cancer cells in the body, and I was thinking of trying a 1 day fast, then later a 3, and moving to 5 if 3 was ok for my body. I’ve drank a LOT of alcohol in my life and feel like it might be a good way to wipe out some of the damage I’ve done to my body. Just a theory but think I’ll try it.

Grant
Grant
7 months 17 hours ago

Great post. Thank you, Mark, for covering this. Very interesting as well.

Scott
Scott
7 months 17 hours ago

I underwent chemo after seeing your previous information about fasting into treatment. 48 hours in and 24 out and I had very few food related side effects. When I didn’t fast things were horrible. I want to thank you for sharing all the information in your blog. It’s so inspiring and informative.

Dave Martin
7 months 16 hours ago

I pretty much fast every single day until 1-2 pm. I normally wake up around 6:30 every morning. I drink a cup of black coffee and water throughout the day. Sometimes I will have a Bai 5 cal drink that has some green tea in it for the caffeine effect.

I’ve been super focused at wok ever since incorporating intermittent fasting into my daily routine.

bill
7 months 13 hours ago

Here’s Stephen Phinney’s take on fasting
at about 1:10:

https://www.youtube.com/watch?v=Qk0U006YZ2w&feature=youtu.be&t=57m59s

Talitha Butterfield
7 months 13 hours ago
Just read Dr. Jason Fong’s book on fasting. He is a nephrologist and works with a lot of diabetic patients with some really fantastic results. I feel the book is really good as he addresses all kinds of fasting and the results he’s gotten over many years with different kinds of patients. People with medical conditions should work with their doctors especially anyone on medications. Otherwise, most fairly healthy people can try one that appeals to them. He explains what to watch out for, has people continue with exercise has recipes for people doing intermittent fasting and some advice on… Read more »
Tee Dee
Tee Dee
6 months 3 days ago

I think that people who are calling IF a fad or not a real fast because some people have the bone broth, cream in their coffee, fat, etc. need to realize that Dr. Fung makes it clear that those additions are ‘only’ to help some people comply, so they’ll get ‘some’ of the benefits of a water-only fast. He would rather that people take only water during short fasts up to 3 or 4 days.

Wendy
Wendy
7 months 11 hours ago

Great topic! I just read in Scientific American about Longo’s recent study about 5-day semi-fasting (1,100 cal first day, 700 each subsequent day) to delay aging processes; published in Science Translational Medicine. Seemingly terrific results for relatively short periods of calorie restriction, and quite importantly as you mention, very low incidence of lean muscle reduction.

AnnaBecker
7 months 10 hours ago

Personally, this doesn’t appeal to me. I believe if you eat right and get exercise, your body pretty much heals itself. There are exceptions, some may be noted in this article. But if you are eating right and moving, I doubt you’d need this extreme of a regimen.

Hannah N..
Hannah N..
7 months 10 hours ago
I did my first long fast as a freshman in seminary. Then I had my first baby, and 10 years went by without any more fasting. Starting three years ago, I got back into fasting and I have done perhaps 5 to 7 one week long fasts. I have found them to be strangely quite easy, and all but one of them I have done while working. My reasons for doing so are more spiritual than health-related, but I feel that they have improved my health as well. Additionally, I lift weights, and during the same period of time of… Read more »
John
John
7 months 9 hours ago

And you should don’t not stop using double negatives.

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