How Intermittent Fasting Affects Your Body and Brain

Published on Dec 20, 2017
Stars like Beyonce and Hugh Jackman have spoken out about following intermittent fasting plans to get in shape. How does intermittent fasting work? Here's what actually happens to your body and brain when you fast. Following is a transcript of the video.
How long has it been since you last ate? People who fast intermittently often eat within an 8-hour block, leaving 16 hours of fasting in between. During that 16-hour stretch, their bodies undergo an important change that sets them apart from non-fasters.
Here's how it works.
When you eat, you store some of that energy in the liver as glycogen. But after 10-12 hours of not eating, your glycogen reserves will be extremely low. As a result, you may feel more irritable than normal, a term scientists call "hangry."
The upside is - with little glycogen left - fat cells in your body release fats into your bloodstream. The fat cells head straight to your liver, where they're converted to energy for your body and brain. So, you are literally burning fat to survive.
Blood samples show that people who had fasted for 12-24 hours experienced a 60% increase in energy from fat, with the biggest change occurring after 18 hours. This is the benefit to intermittent fasting because it puts you in a state called ketosis. And it's why researchers think intermittent fasting could be the key to a longer, healthier life.
The process of burning fat releases chemicals called ketones. In the brain, ketones trigger the release of an important molecule called BDNF. BDNF helps build and strengthen neurons and neural connections in areas of the brain responsible for learning and memory. Which could explain why a boost in ketone production has been shown to improve memory in people with early signs of dementia in as soon as 6 weeks. Increasing ketones in the body is also a common treatment for patients with severe epilepsy.
You don't necessarily have to fast to boost your ketone levels. Introducing more fatty foods into your diet and cutting back on carbs can have a similar effect. A group of people who tried this method for 3 months not only lost weight and body fat, but also saw a decrease in blood pressure and a hormone (IGF-1) that is related to aging and disease.
But scientists have discovered that fasting increases ketone levels more. Ketogenic diets can increase ketones 4-fold whereas fasting has been shown to increase ketones by up to 20-fold. As a result, fasting - compared to a ketogenic diet - may have a stronger, more beneficial effect on overall health.
Yet many Americans who eat three meals a day with snacks in between never reach ketosis, and therefore aren't producing enough ketones to promote good health.
Fasting and ketosis have been a key to our survival from the beginning. They helped our ancient ancestors survive through bouts of starvation.
And today, they're becoming recognized as a way to help keep future generations mentally and physically disease-free.
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  • Hey Tech Insider, Great video. You mentioned that "Ketogenic diets can increase ketones 4-fold whereas fasting has been shown to increase ketones by up to 20-fold" and you showed a graph. Would you mind providing a citation for that finding?

  • I’ve been fasting instead of dieting for years now, but keeping track of everything in spreadsheets and using my watch. So glad I found this app. Makes fasting so much easier to track. There a lots of benefits to fasting besides weight loss from the studies i have read.

  • HECK YEAH! I just started fasting and i feel great, my body is getting more lean and my body fat is getting low. I hit the gym 5 times a week so that helps too!

  • 1400 year ago profit Muhammad nabi teach to Muslims

  • Clear info on intermittent fasting! Compliments :-)

  • I am following this for one month now, and i already lost 8 pounds.

  • Ugh my mother doesn’t let me do intermittent fasting!! She says blah blah I’m going to be weak and starve and even though I keep telling her the scientific benefits of it she keeps ignoring it. Im overweight and my parents keep buying donuts and chocolate milk even though I tell them I’m on a diet...

  • Lay off showing all of the delicious looking food, makes it way harder to fast

  • study sorces pls? i cant find them on your website either

  • Can i still do this but i dont to lost weight just to get into ketosis . Please answer meeeeeeeee

  • Can’t be done every day tho, maybe 4 days a week is best.

  • So yall telling me that I actually haven't been destroying my body by being too lazy to go downstairs for food

  • I love it!

  • Muslims do this entire year and people say this is not rational.

    • Nasir Dar one month (Ramadan) in a year, not the entire year.

  • Can someone just explain it to me?

    • Visual_Z don't eat for 16 hours, and drink water, green tea, and Coffee (no sugar or creamer). Then when you break your fast eat 2 meals in the 8 hour period. While fasting, you'll burn fat and will have stronger immune system to fight diseases.

  • I’m Currently on 41 hours fasting. It’s true feel a lot of energy. I think because I have so many fat cells inside my man boobs lol

  • My best strategy for reaching ketosis, is to eat dinner by 6pm, and not eat until 12 noon the next day. It’s great because you’ll be asleep during most of the fasting period.

  • Finally, after all the none understandable boring long videos on this subject, this one is short, effective and gave all that I needed to know. Thanks very much!

  • I have a question. What if you not able to exercise that much? Will you still be able to fast? Is it bad if you don't? What if you have a strenuous job and need the extra energy? What if you get a headache from not having enough energy? You have to change what you eat, right? What if you have family members that don't want to do it? How will you plan around it? And what if you're on your period? Will you lose energy? Or get sick? Do you have to forego the diet until it stops? What about moodiness? If you have a headache all the time, wouldn't that effect your day? What if you have cravings? Can you be lenient? What about eating out? When will be able to do that? Does it work in people who have illnesses like anemia? What do you do if they get dizzy? Or have a nosebleed? Is it because they don't exercise? If you do decide to exercise, how intense should the workouts be? What if something happens and they can't exercise or do the diet and have to stop? Is it bad if they stop? Should they not do it then?

  • What if you keto and fast ?

  • As per Islam sunnah Our beloved messenger huzoor Mohammed sallalAllah Alaihiwa sallam prescribed fasting twice a week on Monday and Thursdays - what a great recommendation SubhanAllah to keep healthy suggested more than 1400 years ago now discovered by science

  • Bro, do you even FAST??

  • i've fasted 16/8 and 20/4 interchangeably for a year now, and i feel lethargic and too full if i eat 3 meals a day

  • You fooled me by that Wolverine thumbnail!

  • What about a keto diet and fasting together ?

  • Follow my intermittent fast weightloss journey everyone!

  • Well explained!

  • Muslims do it all the time😊😊

  • I eat from 10 am to 6 pm. It is the only thing that keeps me consistently lean without feeling super deprived. I can also eat pizza, cookies etc here and there. A diet restricts these foods and when you start eating them again you increase your weight. Fasting is the long term solution.

  • I am 17 years old .Can I use it?

  • If anyone can answer this it'll be great... So I do IF mon-sat, and fast for around 20 hrs... BUT Sunday is my cheat day.... And I found that I go into a food coma alot more easier than i used too... Is that because my body adjusted to the IF???

  • so how often should you do it? everyday? once a week? twice a month?

  • can i still go to the gym and train while on intermittent fasting?

  • Did I i just see a burger with fried rice on the side? Lol

  • Eating nowadays seems complicated af

  • But what type of food can you eat after a 16hr fast? I been on Keto diet before and cut out a lot of Carbs! So can you really eat carbs after fasting 16hrs? The graph shows a huge increase larger than the Keto diet.. I’m trying the Keto diet again where I’m eating very little carbs per day even after fasted period.

  • Are there any studies of this improving blood circulation because my sex performance and erection has improved from this and im 40.

  • I experience a lot hangry pains lol. Ketones occurs after not eating for 3 days and it does wonders

  • This has been taught since 1934, read "How to Eat to Live" by Elijah Muhammad

  • What about ketoacidosis, when your body uses the fat yes it uses ketone but it also produces acid, which causes ketoacidosis. This will cause metabolic acidosis. Can you guys give me more information on that ? Because isn't that dangerous to your body.

  • But is it safe to exercise while fasting ?

  • Tell that to vegans 😂😂😂

  • reference specific literature not just random academic institutions lol

  • How can you still build muscle while fasting? You can't get enough protein in that short eating window right?

  • Still, being hungry sucks and eating food is awesome

  • But I’m bulking

  • Ketones make your breath reek tho... Oh well.

  • I've been fasting for over 35 years from 2 meals a day to 21 days drinking only water. As I get older, I found it quite rewarding to get my memory sharp and I just keep retaining vital information. I became a firefighter at 51 years old...!!

  • Well you had me at ₩olverine 😋

  • Fat muricans LUL

  • Muslims have been doing this for over a thousand years!

  • That means we do IF during Ramadan yooo! Love my religion.

  • Eating like a poor person is now trendy.

  • I just don’t have access to a gym or my own vehicle, so it’s hard to be to fast this method. When I get older I’m definitely going to try.

  • I've been doing it for over a month today and have lost a stone in weight, it definitely works! Thanks for the avocado tip :)

  • Interesting love it

  • This is nothing but quackery the keto diet is a quack diet if you're diabetic you definitely can't eat this diet

  • Sorry but jack blatantly hit clen 👍

  • What’s a good way to fast but still go to the gym / do cardio ? Pls respond I want more ketones

  • I've been doing this for so long and I didn't even know feels natural

  • This is groundbreaking. Who knew that not eating for long periods of time will cause you to lose weight.

  • how about keto diet with Fasting :D

  • Also know as Third World life style.

  • Muslims did it first. Not to live longer and healthier, but to please God.

  • Wow! Didn't know that. I have been eating 1 big meal , once a day for years .

  • I will only trust this when we can do long term studies on the effects

  • :o

  • Only drink water during your intermittent fasting window. Things that stimulate metabolism will reduce ketosis's effectiveness. So no black coffee, unsweatened tea or sugar substitutes like Splenda. Just water. But if u get head headaches take some sea salt. Might reduce ketosis but having pain will drive u to eat which breaks it.

  • love and peace to all from Pakistan.... hate or love it I just did a favor to you all

  • Bible don't have no such indications and guess which book does well that's the book most Americans never find easily accessible.. because for just one reason and thats is because you may revert to Islam after finding out what theirs book has to offer to humanity unlike Bible which gets a bit behind and whole alot confusing... check out Jeffrey Lang on US-tv to find out what book has mentioned abt this scientific fact and many mind boggling Truths and fact purposely Westerners we're kept away from and why,,,,,, I am not just mentioning the name of the book here at the moment....

  • What Joe rogan keeps going on about

  • No scientific study needed. Just eat a meal a day like the olden days. Simple as that. The agriculture lobbiests taught us to eat xx amount of meals and xx amount of each food group which is false. How else you think people in other parts survive.

  • Is it okay to at least drink water during the fasting time? Sounds dangerous if not

  • Why do they show food commercials on these fasting videos 🤤

  • My only problem is with smoking. I can fast for days and I've tried many fasting diets but smoking on an empty stomach hurts a lot and I've tried cutting cigarettes but without any results🤦‍♂️

  • I only eat twice a day with a 16-hour fast and an 8-hour window. It all started 6 years ago in college because of my shitty class schedule.

  • It's quite a relief knowing that fasting can be more effective than just a keto diet. If I only eat in a 6 hour window, I can simply have a low carb diet instead of torturing myself with strict keto.

  • Kinobody is gonna like this

  • I'm pretty sure it's not scientists that use the word "hangry", but feel free to pretend it's not a bastardization of the English language.

  • My strength in the gym is literally half when I do this. Wtf?

  • This is bullshitt

  • This guy PBUH did this often 1400 years ago and has prescribed people to do this one month out of the year. But now it's a proven health benefit. Thank you God.

  • 20/4 intermittent fasting is the one for me 😊

  • ''a term scientists call ''hangry'' '' millennial youtube scientists that is

  • Islam said this 1400 years ago. 🤷🏼‍♂️

  • Does anyone have any peered reviewed articles about intermittent fasting and its effects on hypothyroidism?

  • What about people who fast until 8 for an entire month? (Ramadan. . ?)

  • Just finished day 1 easy.

  • Praise God

  • Keton diet is the worst for any human being. You won't live for longer than 30-50 years if you wanna live on a keton diet. Not to mention the chronic diseases you will live with.

  • In ramadan we fast the same but with no water, from the sunrise to sunset is approx 15 hours.

  • Recent researches are just finding out some good habits that have already been prescribed to Muslims centuries ago

  • U know alhamdullilah ramzan is also meant for this

  • I will do this more

  • I eat a heavy breakfast around 9AM and I skip lunch and eat again a heavy dinner at 6PM. Does that count?

  • so I've been doing this and I didn't know what to call it

  • Ive been doing this for years, now people are calling this the "silicon valley" diet

  • That's why Muslims fast

  • Kinobody

  • I found the most effective way (for me) is to eat at least 60-70% of my daily calories in my first meal, eating between 5-6 hours AFTER I wake up and eating the rest of my calories for my dinner. I’ve been doing this for about 2 months and I’ve lost 20 pounds, I have way more energy, and my workouts have become more efficient and starting to see massive changes