The Truth About Fasting: What Really Happens to Your Body?

Check out these incredible health benefits of fasting, and learn why these effects of fasting occur.

More Videos on Dawn Phenomenon:

Growth Hormone and Fasting:

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0:05 Fasting explained 
0:38 Effects of fasting after 12 hours 
1:21 Effects of fasting after 18 hours
2:37 Effects of fasting after 24 hours
6:23 Effects of fasting after 48 hours
6:54 Effects of fasting after 72 hours
7:24 How to get these incredible effects of fasting

In this video, we’re going to talk about what happens on the inside of your body when you’re fasting. 

There are a lot of beneficial effects of fasting on the body. Over a long period of time, the human body has developed and adapted to starvation. However, our bodies have not adapted to frequent eating. 

What happens when we fast?

Effects of fasting after 12 hours—There is a spike in growth hormone.

Growth hormone is involved with:
• Anti-aging 
• Fat burning 
• Healing joints
• Protein synthesis 

Effects of fasting after 18 hours—You develop autophagy.

Autophagy is involved with:
• Recycling old and damaged proteins as well as microbes
• Decreased amyloid plaquing 

Effects of fasting after 24 hours—You really start to deplete your glycogen reserve and run on ketones. 

Benefits of fasting after 24 hours:
• Decreased hunger
• Decreased cravings 
• Increased antioxidant reserve
• Increased oxygen 
• Better fuel efficiency 
• Decreased inflammation 
• Gut healing 
• Improved cardiovascular function 
• Improved cognitive function 

Effects of fasting after 48 hours:
• Stimulate stem cells
• Decreased risk of cancer/tumors 
• Make more mitochondria 

Effects of fasting after 72 hours—Do periodically 
• More stimulation of stem cells 
• Better immune function

How to get these incredible effects of fasting:

• Do intermittent fasting on a regular basis
• A good average pattern of intermittent fasting is doing 18 hours of fasting with a 6 hour eating window
• Do periodic prolonged fasting to achieve additional fasting benefits 
• Take minerals during fasting (water along with nutrients ) 
• Exercise in the mornings 
• You may have increased LDL (This may not be something to worry about)

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Dr. Eric Berg DC Bio:
Dr. Berg, age 56, is a chiropractor who specializes in Healthy Ketosis & Intermittent Fasting. He is the author of the best-selling book The Healthy Keto Plan, and is the Director of Dr. Berg’s Nutritionals. He no longer practices, but focuses on health education through social media. 
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Dr. Eric Berg received his Doctor of Chiropractic degree from Palmer College of Chiropractic in 1988.  His use of “doctor” or “Dr.” in relation to himself solely refers to that degree.  Dr. Berg is a licensed chiropractor in Virginia, California, and Louisiana, but he no longer practices chiropractic in any state and does not see patients so he can focus on educating people as a full time activity, yet he maintains an active license. This video is for general informational purposes only.  It should not be used to self-diagnose and it is not a substitute for a medical exam, cure, treatment, diagnosis, and prescription or recommendation.  It does not create a doctor-patient relationship between Dr. Berg and you.  You should not make any change in your health regimen or diet before first consulting a physician and obtaining a medical exam, diagnosis, and recommendation.  Always seek the advice of a physician or other qualified health provider with any questions you may have regarding a medical condition.

Thanks for watching! I hope this video helps you better understand what really happens during fasting.

Dave McKinnon

  • EverythingTek says:

    I rewatch your fasting videos again while fasting to remind me that I’m doing the right thing for my body and gives me motivation to continue

  • Jah Pards says:

    My deep respect to doctors giving information to people for free. It means they really do care. 🙌

    • djmeechymeech says:

      Doctors are making more money in YouTube than with their own salary these days.

    • Abhi Tiwari says:

      Youtube monetized

      Just kidding😁

    • Shin Jara says:

      Helping while earning…. A LOT.

    • Ruderaksha Karwa says:

      I hope he makes a lot of money. He deserves it

    • Ken Cramer says:

      I nearly didn’t watch this because there’s usually a catch or commitment in exchange for info. But this guy is generous. It’s because he’s not selling something (other than free health) he definitely deserves success. So then where’s the revolt from the market place because they stand to lose much to something that is free.

  • Exposing Liars says:

    I was gaining weight, doing too much cardio and fatigued. I stopped all exercise and went zero sugar and fasted and lost so much inflammation and weight, even without exercise. He is telling the truth.

    • play station says:

      Now be careful with the food else you will gain it back so fast. Good luck.

    • Anonymous says:

      The keystone to losing body fat is hormones the main one being insulin. Insulin in the body is primarily used to convert the glucose in the blood to a form of fat to store in the adipose tissue. This fat storing hormone production is increased when a person becomes more insulin resistant. So to lose body fat it is important to become more insulin sensitive. Fasting, eating a lot of high fiber foods, and walking a lot for exercise are a few things that will reduce insulin resistance.

    • Paul Mews says:

      Problem with just exercise is that people think because they are exciting that they can eat unhealthy foods. The reality is that it’s 90% about the foods you eat. I disagree with fasting though, it will bugger up your metabolism if you constantly go in and out of fasting. I ate 5 times a day and lost 9 stones in 5 months. Bit I proportion controlled and ate low calories for that period, coming out of it slowly, eating healthier foods. But wouldn’t just fast. You should eat something every few hours to keep the metabolism ticking over.

    • Threetunes says:

      A large part of the problem is sugar, and high GI foods in general. As was mentioned earlier, you want to limit your body’s production of insulin while you’re trying to lose weight.

      Eating high GI food causes an insulin surge which turns off your body’s fat burn mode. It almost doesn’t matter how much you exercise, as long as you’re spiking your insulin levels you’ll have real difficulty burning fat as your body just won’t do it until its got the right conditions to do so.

      Just draw up a list of high GI foods and limit your intake of those foods, particularly on cardio exercise days. For lifting weights or being competitive with others I don’t really care about limiting GI intake though.

      That works for me. Simple enough to actually stick to and it works.

    • vatoLoco says:

      Today is my first day..i wana experience it too..

  • Canadian Renegade Hunter says:

    I majored in Biology, submolecular, human anatomy, McGill, this video is a great explanation of precisely what occurs during fasting 👏

    • V C says:

      Can you confirm if this is based on complete abstinence from
      Food or does this also apply to intermittent fasting as well?

    • Canadian Renegade Hunter says:

      @V C intermittent would be the best term, when testing certain smaller mammals in trials, after a certain amount of time, the brain can render your cognition unresponsive, due to lack of water, proteins and good cholesterol.
      The synapses will intermingle in a violent fashion and may result in aggressive and impulsive behaviors.
      I strongly suggest intermittent fasting, It seems the shock to the body from long time fasting can be harmful in instances where the body, is already in need of vital nutrients.
      Eat a well balanced diet in your usual form,.this way the body has the required back up nutrients for your fasting.

    • Denisa Nica says:

      @Canadian Renegade Hunter thanks for these clarification. What does “after a certain amount of time” mean concretely?

    • Dont be fooled By Jumla! says:

      Thanks any medical books in this

    • Andre @JKT says:

      What are the sources and research for the autophagy and fasting mechanism/causality? Not passing judgement, but this Dr. explained it like its common medical knowledge but i dont think it is. It would be more credible if he provided research citation.

  • Lisa Johnson says:

    I started intermittent fasting since September 2021. now I’am on 24 hours and my body start telling me some days that I’am ready for the 48 hours. I feel great and lost 40 pounds 🥳

  • Russ Wood says:

    I did my first 24 hour fast this week. I don’t think I would have been able to do it without watching this video and another video Dr. Berg made about fasting. I now plan to do a 24 hour fast once every three months. Thank you Dr. Berg!

    • D' La Torre says:

      Keep doing it, i have done it and lost 50 pounds doing fasting for 16/8 20/4, omad, exercise, don’t give up!

    • Arm Prakash says:

      @D’ La Torre could you please explain about 4hrs eating window? For an instance, if your eating window is from 12pm to 4pm then you will be having your first meal at after 12pm and second meal at before 4pm?(finished second meal at before 4pm) Is it? If that so, then how you will get hungry in that short period of time for second meal…. Please clarify..🙏

    • Phnerdbutt_46 says:

      @Arm Prakash I eat 20/4. I eat a rather big meal at noon and a high fat smoothie just before 4:00. That keeps me satisfied until noon again the next day. And I am quite ready for that smoothie at 4:00 even though I had eaten at noon.

    • MrGoodeats says:

      @Arm Prakash oh you’ll be hungry

    • Ashutosh Mohanty says:

      Why not once in a week?

  • Todd Denny says:

    Very grateful to Dr. Berg for making this video!! Very informative and hard to find insights into fasting! I’m skipping dinners often now, my last meal is by 3pm. Waking up early and eating at 8am gives me a 16-hour fast easily. I’m 65, thank you very much 🥰

  • Enos Anderson says:

    I am 69 years old and I have been on the 18 hour IF diet for over a year. I started the 72 hour fast about 5 years ago and continue to do that every 6 months. Many of my friends ask what is my secret. I have never felt better. My fasting was not to lose weight, I just wanted to be healthy.

  • Disco Tek says:

    Actually doing it now for the 4th time, currently in my 58th hour, this time I am going for 96 hours. Thank you dr. Berg for all the videos and good energy!

  • Luan Klobucishta says:

    I am Muslim fasting it’s one of the regular habits that we integrate in our lifestyle I fast every Monday and Thursday regularly the day after I feel great this is very true I’m glad I came across this video!

    • Thomas Franche says:

      Catholics fast during Lent.

    • Brzahf Foods برزیف فوڈ says:

      MashAllah 💕💕

    • Koda Muru says:

      Yes, in Hindhuism is explained how to fast n how to break the fast thousands of yrs ago.

    • Howl Pendragon says:

      @Koda Muru it’s not the same. In Islam you don’t get to consume anything from dusk till dawn for a whole month. Once the sun sets we can break our fast. I haven’t met a Hindu who did the same except they eat only vegetables.

    • r/FuzzyBearX says:

      @Howl Pendragon Yh but when’s use eat at night use go crazy, it’s better then nothing but can be damaging depending what use eat every night plus a proper fast is no food for over 3, 5, 7days plus.

  • Marsbars says:

    Thank you Dr Berg, I am a GP, two years ago I was diagnosed with multiple precancerous polyps in the colon. I have been following your intermittent fasting recommendations. The polyps I have after 2 yrs are simple ones and smaller in size. My screening colonoscopy recommendations have gone from yearly to every 2 years and now every 3 years. God bless you sir and thank you. ❤

  • Eugene Kim says:

    Nobody can explain in such clear and meticulous manner as Dr Berg… thank you for the video!

  • NfiniteRage says:

    I started fasting in July of this year. I went to the doctor last week and I found out that I lost 30 lbs. This really really works I can’t believe how something so simple as not eating or controlled eating has drastically changed my life. I did 18:6 and 20:4 switching between the two non stop since July and I’m down 30 lbs. I am so very proud of myself and now I want to see if I can lose a bit more.

  • Aadya Sharma says:

    *Third time trying a 72 hours fast! Watching your videos again cuz you give us motivation & inspiration along with all the knowledge! 38 hours & going strong*

  • N says:

    I am 49yo. Fasting every Wednesday for 20-24 hours (drinking only water) for more than 3 years now. Added Friday in the last 4 weeks, so 2 days a week now. I had never felt better in my entire life. I lost 7 kg (I am 170cm/63kg), feel very energetic, sharp minded, more disciplined and organized. Combined with daily meditations I am doing for a year now and tracking my sleep thru the app on my apple watch for 2 years, my life changed forever. People get shocked when I tell them my age, nobody gives me more that 35. I love my life and enjoy every minute of it! Good luck to everybody who decided to challenge themselves and start intermittent fasting! And Dr Berg, thank you for the great video!

  • Adekanbi Julius says:

    Thanks doc for making such information so free. I burned a lot of fat and dropped over 20kg in a year, just by fasting and taking walks, I never felt any better! 💪🏽🔥

  • La IsHighlyFavored says:

    Just a little over 6hrs left in my first 72hr fast! I can’t believe that I actually did this, all thanks to you Dr. Berg. ❤

    • Cherry Mama says:

      That takes so much self-control. You should be proud of yourself!

    • The Roaman says:

      Was it hard?

    • gs gs says:

      Can take water or fruits juice during fasting…pls advise

    • Isabel Breit says:

      @gs gs It depends on what type of fast you are doing, I’m on my 3rd day of Dry Fast, no water I only brush my teeth, I feel great, not hungry at all, have no headache, and not tired, my vision is becoming sharp and my brain fog is gone. I do light exercise for 30 minutes to avoid muscle waste but avoid sweating. My mind is sharp, it’s good to be busy during fasting. My goal is to do 7 days but I’m not sure yet if I will be able to do it. I tried fasting with liquid only before and I felt hungry all the time and had lots of cravings so it’s amazing how easy has been to do this dry fast for the first time. You can do your fast for 16 hours to start and add time every day and drink liquids but avoid sugar in my opinion.

    • Gershy Zilber says:

      @gs gs no water only I’m almust at 64 hours feeling great no cravings at all

  • Smarttech says:

    Hi I m Muslim and during Ramadan I loose 20+ lbs and I feel great , so even doctors recommend fasting against cancer , few of my friends not Muslims are fasting this month and I m here to help them with any questions they have they never heard about fasting , so I shared this video with them and they love it they said they feel more alert more energy , first few days you may have headache no coffee but if you take dates in morning 1 or more they have all benefits in it to keep you going thru the day .

    • Sofi Andi says:

      Ok,I argued with a friend…not eating is ok,i totally, absolutely agree but what about water drinking? Does it not cause health issues? Not drinking for so many hours?

    • Not me says:

      @Sofi Andi I dont think that would be harmful unless you or anyone have an health issue that forbids going on for hours with no water other than that I see no issue whatsoever

    • meisa says:

      @Sofi Andi u can survive without water for 3 days straight, plus we drink alot of water during our predawn meal. its only for a couple of hours so its fine. fasting keeps u energetic too and theres no need for water until you’re able to eat/break ur fast

    • murat aslan says:

      I eat five dates and drink two glasses of water in the sahur, I feel good all day, ıf you dont healt problem try thıs

    • Smarttech says:

      @murat aslan MashAllah I can’t do it 5 no way not even 3 , I have small cup of black coffee 2 water and 1 date and I m perfectly fine all day Allah made easy on us if we really doing it for his sake , even my kids fasting every day they will be so upset if I don’t wake them up on sehur , like I mention in previous comments I have few American Christians friends fasting and I text them every morning 4:30 am to wake them up for sehur and then I text them up at night when time to break fast this ramadan it’s easy MashAllah thanks Allah for everything and mostly for health and good he provide to us , after fasting we appreciate everything we have way more

  • Oyungu Mike says:

    I have just found this amazing, informative video out of my curiosity!! Am a Christian but decided to join our Moslem brothers and sisters during this Ramathan and am in day 2 of fasting. My weight is dropping tremendously and am feeling all freshened and energised. I pray Allah guides me through.And to my late maternal grandpa who was a Muslim (Alhaji Alhai jabir) I dedicate this fast to you🙏🙏

    • Anzumi says:

      Its amazing me too i start fasting during ramadan.

    • Natasha Murphy says:

      Orthodox Christians have more fasting days in the year than non fasting days. You don’t need to join Muslims, ancient Christianity have the fasts.

  • adrian clay says:

    Just finished a 40 hr fast. Water only, carried on working, felt great. My internal body and mind feel refreshed and cleansed

    • Devonian says:

      Did you use a ‘lemon water’ lol ie with added sea salt and squeezed lemon juice Dr Berg did a video on it and it stuck with me for some reason.

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