Don’t trust your gut.
Motivating yourself to “starve” for days on end is tough because the benefits of prolonged fasting don’t feel big enough to offset the downsides.
It’s harder to feel fasting’s long-term health benefits than it is to feel hungry now.
And it’s harder to feel fat burning than it is to feel satisfied from delicious food.
But trusting your gut’s probably what’s gotten you into the trouble you need fasting’s help to get out of. Feelings are unreliable. The truth is the benefits of prolonged fasting far outweigh the disadvantages for most of us.
So how do you feel it?
The better you understand the benefits and disadvantages of prolonged fasting—including ones most first-time fasters don’t think about—the more likely you’ll stop trusting your gut and make the right choice.
In This Post
Why Not Not Fast
You Might Starve to Death
This is the most bogus excuse people use to avoid trying a prolonged fast.
While I can’t promise any of these benefits of fasting, I can promise one thing: You won’t starve to death by not eating for a few days.
For perspective, the world record for the longest fast ever is 382 days.
Here’s why you won’t starve:
The average human has 34 pounds of fat. Each pound is good for 3,500 calories, or about two days’ worth of food. So we’re like hikers lugging around backpacks with 68 days worth of snacks, just in case. It won’t kill us to lighten our loads by consuming a bit of it every once in a while.
More likely, it’d help.
Why Not Fast
Before getting to the benefits of prolonged fasting, let’s be realistic and safe. Here are the reasons you might want to hold off on it.
✗ To Lose Tons of Weight Immediately
If your chubby butt goes on a 5-day fast expecting to have a 6-pack after, you’re going to be disappointed. As just explained, you can only expect to burn half a pound of fat a day from fasting.
✗ Going Cold Turkey Sucks
If you eat a lot of processed foods and snacks all the time, your first couple of days of fasting might be rough. You may feel hangry, lethargic, brain-foggy, and even nauseous from going cold turkey on that junk.
Kim experienced this on her first three-day fast.
To avoid similar misery, wean yourself off bad eating habits before trying a prolonged fast and check out my Easy Water Fasting Tips from a Guy Who Learned the Hard Way.
✗ You Want or Have a Baby
Prolonged fasting may have adverse effects for women who are pregnant, trying to conceive, or freezing their eggs. It may not either. The science is limited and female fertility is complicated. But the safest bet is not to risk it.
✗ You Have a Medical Condition
If you’re on medication, wait until you’re back to normal before fasting. At the very least, consult with your doctor.
✗ You Have Serious Self-Control Issues
For many people, the self-control training is a benefit of prolonged fasting, but if you have serious doubts about your self-control and fail early on it’ll only make you feel worse.
If that’s you, start with a less-extreme goal like cutting snacking for a few days. Once that’s easy, try intermittent fasting—only eating between 12 and 8 p.m., for example. When that becomes easy, go for a prolonged fast.
✗ You’re Susceptible to Eating Disorders
The feel-good benefits of fasting can be addictive, maybe too addictive to some.
Fasting-ating Insight: “I’m really enjoying the benefits and extra energy and at this point, feel like I could continue for quite a while but fear permanent damage to my body. (I’m afraid to ask my doctor about this or he’ll think I have an eating disorder—I’m not overweight or anything.) Or how do you know if you’re actually developing an eating disorder? It’s starting to feel too good not eating…” – LA Girl commenting in our Water Fasting Tips post.
✗ You Have a Big Race, Presentation, or Building Ahead of You
The extra jitters some feel might affect a presentation. Pushing your body on a new fuel source (fat instead of sugar) may be pushing it too far. And nobody wants you to get light-headed as you’re operating a crane swinging a wrecking ball at a building.
✗ You Have a Hot Date
Bad breath is a common negative side effect of prolonged fasting.
Mask it with mouthwash or breath mints if you must, but a) that only lasts for so long and b) it’s hard to have a hot date without food.
✗ It’s Bad for Business
The number one reason why more people don’t fast is Big Pharma and Big Food can’t make money from people not consuming anything. No money means no Super Bowl ads pitching the benefits of fasting.
A couple of noteworthy people who have made a business of telling people not to spend money on food:
- Dr. Jason Fung. His books on fasting, The Complete Guide to Fasting, and weight loss, The Obesity Code, are easy-to-understand, motivational, and worth forking over some money for.
- Dr. Valter Longo. When his research subjects were having a hard time sticking to the fasts he needed them to do, he devised a “fasting-mimicking diet” that allowed them to eat something and still get many of the same benefits of prolonged fasting. Then he set up a business selling this 5-day fast food package, donating his share of the profits.
Benefits of prolonged fasting that you may not have considered and that may shut your trap—from excuses and food—for a few days.
Big Fat Warning:
I can’t guarantee any of these benefits of fasting.
Everyone reacts differently. Factors like diet, fitness level, fatness level, genetics, time of the month, if your boss is a prick or not, whether you’re a cat or dog person, and your hairstyle will affect your experience.
This uncertainty is part of the adventure. For some, it’s another reason to fast.
And there’s always an easy fix if your fast becomes a disaster: Eat.
✓ It’s Not Complicated
✓ It Gets Easier and Easier
The first fast can be tough for some (like Kim), but the more you do it the easier it becomes. (I’m still working to convince Kim of this).
I honestly look forward to periodic prolonged fasts as a mind and body cleanse.
✓ It’s Better Than Free
Fasting isn’t just free; it saves you money. Few other health and spirit boosters, like working out outside, can claim the same benefit.
✓ Productivity Spikes
Firstly, fasting saves time. Less time preparing and eating food means more time for other things. It saves so much time that I sometimes wonder what to do with it when I’m fasting.
Secondly, after you overcome the sugar withdrawal stage, fasting can make you feel sharper. All the energy that’s normally used by your digestive system gets channeled to your brain. Instead of running on sugar your brain will start running on ketones, brain rocket fuel. For me, it feels like I’m on Adderall.
Fasting-ating Insight: “I schedule my 48-hour fasts for a tough weekend at work, and my mental acuity and mood are GREATLY enhanced during that time” – Comment from reader Leigh
✓ Crack Your Addiction to Food
Hunger has nothing to do with an empty stomach. It’s psychological.
That’s why you can feel just as hungry for lunch as for breakfast despite having eaten more recently.
The hormone most responsible for your hunger pangs has a fittingly goblin-esque name: ghrelin. Ghrelin comes and goes cyclically based on your daily eating routine. Fasting screws up this cycle. Screw with it enough and it stops.
No more hunger pains. No more addiction to food. You’ll enjoy eating just as much but only feel the need to do so when it’s convenient, not when ghrelin tells you to.
Fasting-ating Insight: “My three-day fast ended up do a 7-Day fast because I had no complications and felt great! all my friends cannot believe I went 7 days without a single morsel of food! What an experience!” – Comment from Mike
✓ Spiritual Rewards
Undoubtedly the world’s number one reason for fasting is religion. Many of the world’s religions incorporate it somehow.
It’s no coincidence. Even if you’re not religious, like me, the mind-opening, habit-challenging stimulation of fasting can have serious spiritual rewards.
Fastin-ating Inspiration: “My mind feels clearer and more relaxed. Fasting feels wrong, but my body and mind are enjoying it.” – Comment from Sandra
✓ Satisfy Your Curiosity
What does it feel like to not chew for a few days? Do you need to brush your teeth if you haven’t eaten anything? How does it feel when your stomach caves in as your organs shrink as they dump water and regenerate? Does the mental high of fasting really feel like being on Adderall? Do you still take shits?
Any curious person who lives by the motto, “I’ll try anything once,” needs to try fasting to get the answers for themselves.
✓ Clean Out Your Garage
Fasting gives your poor digestive system a break. It’s been working non-stop your whole life and could use some time off. It could also use some time to clean itself out and dump the unnecessary junk that’s been accumulating over the years.
And I mean dump. Many people report unusual bowel movements later into their fasts or soon after refeeding.
✓ Recover Better
When you’re sick, you often don’t feel hungry. That’s your body telling you to stop making it work on digesting food so it can focus on more pressing issues.
✓ Easier Travel
When you become a master fast-er and kick your hunger addiction (a benefit of fasting we already covered), you don’t need to worry about bringing snacks with you everywhere or plan your travel schedule around mealtimes. And you don’t get hangry.
✓ Recycle Yourself
When you fast long enough, something called autophagy happens. Autophagy is Latin for eating yourself. But unlike some lonely Hannibal Lecter, this type of self-cannibalism is healthy. Your body finds and feeds on the damaged and old cells.
If left to accumulate and fester, these junky cells can lead to degenerative diseases like Alzheimer’s and cancer down the road. So eating them may reduce their incidence. And, since you grow new cells to replace the old ones, you’re better than ever.
It continues, too. Fasting stimulates the release of human growth hormone, which will help you continue to rejuvenate and grow even after you’re eating again.
✓ A Desperate Last-Ditch Attempt
Many people’s online accounts report fasting relieved their knee pain, toothaches, bad skin, and arthritis. None of this is guaranteed and you and your doctor can probably find better solutions, but if you’re desperate, fasting may be worth a last-ditch attempt.
For instance, this guy did a 7-day water fast out of desperation because of a sore back and claims to have experienced inspiring results:
Fastin-ating Inspiration: “I did a 10 day bone broth fast in the summer of 2016, two of those days actual fasting, and it was the beginning of a life-changing transformation. I went from thinking I was going to have to retire early from pain to being pain-free.” – Comment from Emily
✓ Rekindle Your Love for Food
Absence makes the heart grow fonder so, for many people who do prolonged fasts, that first bite of food after days apart is unforgettably delicious.
Fasting-ating Inspiration: “Honestly the toughest part for me isn’t being hungry, it’s just missing food and flavor.” – Comment from Jon
✓ Spread the Movement
Since no big business is going to start advertising fasting anytime soon, it’s up to us to spread the word. And the best way to do so is through our actions.
When family and friends see me fasting, they mostly think I’m crazy, but some will allow a seed of doubt or curiosity inside of them. That seed may take root and grow to the point of eventually motivating them to try. And if they experience some of these benefits of fasting, they too will spread the word.
✓ The Long-Term Benefits of Fasting
These long-term benefits of fasting are the real reason you should fast, but sometimes aren’t tangible enough to motivate many of us to do it unless we’re forced to:
- Better blood sugar control. Basically, it trains your body to get better at clearing sugar from your bloodstream.
- Cancer prevention and chemotherapy effectiveness. Fasting seems to cause healthy cells to protect themselves and makes carcinogenic ones more susceptible to treatments that seek to destroy them.
- Speeds up your metabolism. This can increase your energy and lead to long-term weight-loss benefits.
- Relieve inflammation linked to the development of neurodegenerative disorders, heart disease, cancer, and arthritis.
- Live longer. Unlikely to be proven with randomized controlled trials, but a lot of evidence, including all the aforementioned benefits of fasting, points in that direction.
For the nitty-gritty details, this Healthline article has links to a ton of studies on these benefits of fasting.
Fasting-ating Inspiration: “So I’m a 44-year-old male and was at my heaviest last year 210lbs 5′ 10″ which is pretty bloated. My blood pressure has been out of control like around 210/120 and I ended up in the emergency room with no real symptoms but people were telling me I needed to go. So they prescribed medications and monitored me overnight and my blood pressure normalized on Linsinipril to 130/80. This sucks, now they were telling me I would probably be on these pills the rest of my life which gave me every side effect in the book. I did some research on water fasting and found studies that said water fasting does great with out of control blood pressure. I did 3 48 hour water fasts using only distilled water and a pinch of salt. I stopped taking my blood pressure medication during these fasts and found the fasts would keep my blood pressure around 150/95 and when I started eating poorly again it would slowly creep back up. So, I decided to do a 6 day water fast and it was the best thing I’ve ever done for myself. Blood pressure is no longer an issue as it is now 115/75 and hasn’t gone back up after 3 months of eating although I’ve cut out most bad food and mostly eat a vegetarian diet and limit sugar. Great work!!” – Comment from Jeramy Ray
✓ A First Step to a More Extraordinary Life
To live an extraordinary life, you have to do extraordinary things. (Duh.) That means expanding your comfort zone.
Fasting is a perfect example.
Not only did prolonged fasting completely change how I thought about eating, but it also me me wondering what other habits and preconceptions I could challenge.
For some more ideas, subscribe to Consider This, where I challenge you to new ways to break your routine every other week or so.
One Final Question For You
Ask yourself this final question if you’re still uncertain or skeptical about the long-term benefits of prolonged fasting:
What’s the real downside?
Unless you face one of the serious health risks listed under the Why Not Fast section, the worst that’ll happen is you’ll have a crappy day or two feeling hungry until you eat again.
But the upside is huge.
If your prolonged fasting experience goes well, you could feel better than ever, save yourself some time and money, and improve your eating habits for good. And if the uncertain science proves true that prolonged fasting helps you live longer and healthier, that’s just icing on the cake!
28 responses to “Why Fast? Prolonged Fasting’s Surprising Benefits and Disadvantages”
Hi Kim and Chris,
I started Fung’s 24-hour IF schedule a month ago, and cut out sugar, refined flour, and any snacking, and after 2 weeks switched to his “36-hour” (basically every second day) schedule, usually breakfast/lunch around 10:30am or whenever the urge hits, then dinner at 6ish. I am 66 years old, 6’2″, and was 265 lbs. After 3 weeks I reached 240 but then plateaued. Frustrated, I fasted for 2 days, and felt so fine that I considered extending to 3. I decided that if my morning weight had still not budged, then I would. Ît did, so I didn’t, and I am now in the 230s. Still, I was curious, so I googled 3-day fast and found your great writing on longer IF periods. My target is around 200, and I suspect slower progress from now on, but I am thinking alternate fasting days with 1 or 2 3-day fasts per month (many years of dietary sins to absolve as I move into old age!). Adding some resistance training going forward as well.
Keep up the great work!
Hey great read! I’m in day 2 of my first ever water fast, Bizarre feeling but I’m positive.
I’m drinking filtered water through a brita filter with about a teaspoon of pink salt a day spread out over my drinks.
I’m doing the fast because I’ve not been very well recently with gut and liver/bile problems.
I’m uncertain of how much water I should be drinking, I have a blood test tomorrow so we’ll see how that goes and if it’s not looking great I’ll just do 3 days but if it’s okay I may go for 10.
I was thinking half a tablespoon of apple cider vinegar a day to, can I drink tea? And can I use cannabis?
Thanks for everything guys
Ok thx for making me feel better. I have been completely fasting 3 days a week for 5 mts. Straight now . I’ve never felt better. My arthritis in my neck went away over night for real . I had the pain even went to therapy nerve test and neurologist Doctor . For 8 mts.. I have decaf Gr8 teas , decaf coffee and over 120oz. Of water if I were hungry I’ll have low sodium broth but I’m not. I have lots energy, not Cranky, great sleep, not tired . I cook for my family several days a week even fasting no problem . On barge days I eat I eat plain oatmeal made with water, apple , low fat protein, salads, plain dry Cheerios in baggy for a snack and another apple . Snack Also mixed nuts plain unsalted almonds , Brazilian nuts, walnuts . I’ve lost 33 lbs. when I lose another 7, I’ll go to fasting 2 days a week forever . My husband now joins me in Monday’s. I do have 1 cheat day a month on a special occasion. With NO guilt. I’m Assuming that’s ok . Why I decided to do this and made my own diet and I’ve tried all kinds and spent $$$$ . My #’s out high like cholesterol, border diabetes& that arthritis!!! I haven’t rechecked #’s yet. But the arthritis alone worth it .. thx. For reading letting me comment oh I’m 57 but my whole life I feel 20 ..
I’m starting a three day water fast today and was curious if the below supplements are okay to take (they’re part of my regular routine):
Biotin (Trader Joe’s brand, 5 mg x 2)
Psyllium Husk (now brand, 3 capsules – 5 calories per serving – twice a day) The bottle says it has no caloric effect.
Men’s Once a Day Multi-Vitamin (Trader Joe’s brand, doesn’t even list calories)
Other than that I’m planning to just drink: water, black coffee, green tea, club soda, and Ultima replenisher powder (once a day for electrolytes).
Am I cheating on anything here? I started today and have only had coffee and water. I don’t want to muck this up.
Hi Kim & Chris,
I am thinking of fasting for the first time and your article really helped me in making my decision.
Thanks a lot!
will let you know how it goes.
What about drinking coconut water as a cheat/hack instead of using the electrolyte powder? Has anyone reading this tried that out or would the author be able to advise on that?
Goodnoon Mr Chris, It was unprecedentedly convincing article to observe water only fasting. I have been going through such articles every now and then and even decide to follow the fast but I go frail in my decision. Some or the other thing or circumstance distracts me. It was 11:26 am, Monday, 2020 when I had my last meal and took the resolution to follow Lord Jesus for 40 days. I had been an addict of chewing tobacco and even consumed other intoxicants at irregular intervals. There is the KILL THE CAN that brain washed me with its motivating posts and I quit chewing tobacco more than two years before. I have not been consuming caffine for more than 6 months. But to drive the toxins and fats both sub cutaneous and visceral from my body, I took this decision to fast without food for 40 days. I also expect some spiritual and financial breakthroughs as I came to know through the Internet. I want your support and wishes to be persist in my determination. Could I kindly expect this? It would be so kind of you. Thank you.
Lovely and witty article. I have been doing 10 days water fasts once a year. I am currently on my fourth now and it does get better with practice. 🙂
On my day 7 and looking forward to eat on Sunday. I feel great, even when teaching yoga, cleaning house.
Dizzy only in the morning so when getting out of bed I sit for 30 secs before I get up.
Not moving and “preserving” the energy is actually worst. The more I am active (walking in fresh air, even working – easy work) the better I feel and I keep forgetting I am actually fasting.
I love the fasting! The mental clarity after day 5-6 is unreal. I also feed my soul – meditation and also pranayama at least twice a day.
It makes me happy that so many people are now into fasting. Most people around me think I am crazy. I am fairly fit and quite slim so I have to always make sure I explain I am not anorexic or bulimic because most people link fasting with losing weight.
I totally put it back on. So all good.
I healed some eczema, cleared skin, dipped into serenity and calm.
I believe fasting is anti-aging. I am 41 and don’t look it and I hope to fast every year before my birthday. This way I get away from my yearly autumnal depression. It’s like a reset.
Thank you again for leading everyone by giving important info.
Happy fasting everyone!
Great advice; I was thinking of trying a 5 day fast but may see if I can swing 7 days. Also, Dr. Longo’s first name is Valter, not Victor.
Recently came across the ideas surrounding extended fasting. I knew about autophagy from my bodybuilding days and the mere mention of it sent us muscled up Neanderthals running and screaming to the nearest GNC. Fast-forward, I have osteoarthritis in both knees, one which had to have surgery, and osteoarthritis of the cervical spine, which the neurosurgeon wanted to fuse two of my vertebrae with a third in the near future. At 45 years old I wasn’t ready to condemn myself to something that debilitating unless there was no alternative. From my background in anthropology I recalled a professor saying humans were designed for long periods of fasting and stated the benefits to the body so I gave it try. I’ve done multiple 3 day fasts and am currently in what I hope will be a 12 to 14 day fast, it’s okay I have plenty reserve fuel ;-). The 3 day fasts immediately relieved the neck mobility issues and the constant cracking sensation when I turn my head is gone. The knee pain is so slight I foget it’s there. But the greatest benefit has been the mental clarity and relief from my constant ADHD symptoms. Work has been actually enjoyable! Apologies for the long post, and congratulations if you read down to this point. I really enjoyed the article and appreciate your perspective on life. Thanks!
I found your article about fasting because it is motivating to read about it while I’ve embarked my long fasting journey for 2021. I have worked my way to fasting up to 7 days. Since my annual bloodwork and physical is coming, my doctor and I decided to do a 7 day fast prior just to see how my body changes. I am also getting a calcium scan as well. I am fortunate that I found a doctor that has a great interest in functional medicine and is open to alternatives to prescription medicine. I am an ex-cancer patient and not at all really interested in taking chemicals to prevent it from coming back when the same chemicals cause other problems & other cancers. Therefore, I am very keen on allowing my body do the job that it was created to do to a certain extent.
Now to the confession part of this story: Due to C19 and sheer boredom, I gained more weight eating crap. Now I am determined to not only get back to pre-C19 but my pre-pregnancy body. I will be a significant age in a couple of years and hormones are not a friend. Therefore, it is time for me to get my body rejuvenated and prepare prior to the holidays. I love to cook and bake but this year. I figured if I do a long fast prior that my will to moderate the festivities will be greater.
I will say that I did feel pretty amazing on the 7th day last time, not euphoric and am considering trying to go the remaining of the month to lengthen the fast. It is a fantastic challenge between the mind and will. Fasting is not for the weak for sure. For those who are trying to fast, I agree with building up to it. Try OMAD for awhile, then a day or push yourself to 2, then a three, and so on. I got to a comfort level of 4 days and then jumped to a whole 7. The 3-4 day mark, for me was the toughest. If I do a long fast again, which is likely, I will put myself into ketosis for a few weeks and then take another journey. With my age, longer fasts are more beneficial.
My question is (given that you mentioned the potential for what I tenderly call, “fast-shaming”) is how do you do it, stay motivated & communicate your fasting with others? I am not discussing mine this time with anyone but a family member (for safety reasons) and my physician. I am doing this because last time, I was fast-shamed so much. I think I could have gone longer if I had more positive support. Saddening that many, many people seem to overreact to the idea of fasting. Because I would like to try a full 14 days, it is best that I keep this to myself for the most part. I have gotten creative with excuses (not to be accused of being anorexic). Most people know that I am a fan of Keto and OMAD so they don’t invite me out for lunch as often.
Just read your article and liked it.
I am on IF with 20 hrs fasting window since a couple of months. In between I tried long term fast. First time I could fast for 36 hrs. Had to stop it due to severe headache. Second time I fasted for 48 Hrs and wanted to continue further. To be sure if I am aright, I just checked my blood glucose level and it was 58 then. I am not diabetic but I wasn’t sure if this level was OK or not. (It was about 64, after 36 hrs in to the fast.) I checked on google and found some pages mentioning that below 60 is too low and if it drops to 54 it would be an emergency. So I wasn’t sure whether I should continue the fast. Due to the indecision I finally broke my fast. Then later I read some articles that unless the blood glucose level drops below 50 it can’t be considered as hypoglycemia. Today I just started my 3rd long term fast, just 12 hrs in to it.
Did you monitor your blood glucose level during long term fast? If yes what was the lowest reading you got?
I have osteoarthritis of both knees, beginning stage. And due to a small accident my right foot was injured and didn’t heal completely. So I can’t walk more than a kilometre at a stretch. I am hoping that prolong fast will show improvement. I want to fast for 72 Hrs now a few times and then try longer fast. Thanks for your nice article.
Great article. I am an experienced faster, and I am 13 days into my first 21 day water fast. I’ve been feeling great, and I’m really developing a discipline over food and my thoughts that I pray will last for the rest of my life. After my fast, I’m going to choose little moments to continue to exercise the new discipline I have by choosing to NOT partake in opportunities to eat…such as an unexpected BBQ, or pizza party at school. (I’m a teacher) This way, I can continue to keep my new found discipline strong by making small yet challenging situations for me to succeed in. Good luck to all you fasters out there.
I appreciate your humorous articles on fasting and I’m glad I found you. I’ve had Jason Fung’s The complete guide to fasting for a while and I’m now ready to get down to business. Life’s stresses and devastating loses were to great to get started but I’m ready now to heal and get healthy. I believe fasting is a catalyst for my health plan. I have fasted in the past but this will be my longest at 14 days, then I plan on going into a more long term and hopefully sustainable eating protocol with intermittent fasting from then on. Do you have any advise for me and others with this plan for a 14 day fast or longer? I will be under the support of my doctor.