What Happens When You Stop Eating (Science-Based)

What happens to your body if you stop eating for a day, a week, or months? Find out what will happen step by step. Do healing benefits come from fasting for an extended period of time? Discover what the scientific evidence has to say about intermittent fasting, water fasting, and extended duration fasting.

It's well known that when you eat your body begins a series of biological processes to digest and use the nutrients found in that food to help you repair muscle, create new cells, and even store some of the extra fuel as fat for later use. But it's not common knowledge that when you don't eat your body enters a completely different series of biological processes that are just as necessary and beneficial as the biological processes that occur after eating. Of course, if you don't eat for long enough the negative effects will start to outweigh the positive effects, but there are definitely myths and misconceptions about exactly what happens to your body when you stop eating, so today I want to go over that process step by step based on the scientific evidence. 

And first, let's address the conventional advice which would tell you that it’s unhealthy to go for long periods of time without food. And I don't mean days or weeks, I'm talking about simply skipping meals. On the contrary, we've been told that we should eat small but frequent meals. The truth, however, is that there's nothing “natural” about eating five or six meals, spread out evenly over the hours that you're awake every day. This is because, throughout our evolution, we didn’t always have access to food, so you could claim that a “fasting and feasting” eating cycle is more natural than eating breakfast, lunch, and dinner every day. 

Due to the fact that our ancestors had to cope with cycles of food shortage and food abundance, we've developed metabolic pathways that help us cope with prolonged periods without food. In fact, fasting for long periods can actually benefit your health rather than hurt it. But it definitely doesn't feel that way because one of the first things that’ll happen when you stop eating is you’ll start to feel an unpleasant feeling of hunger. Now the intensity of this feeling of hunger highly depends on how accustomed your body is to burning fat for fuel.

You see, most people regularly eat a high-carb diet. So, their body relies primarily on glucose for energy instead of using fatty acids or ketone bodies. Your body has the ability to store a lot of fatty acids in the form of body fat and those fatty acids can be used for energy at a later time when food is scarce by converting the fatty acids into ketone bodies in the liver. But with glucose, it's an entirely different story. Your body can only store a limited amount of glucose in your muscles and liver for future use, and this amount gets depleted after fasting for only about 24 hours but depending on how many carbs you eat regularly it can take as little as 8 hours or up to 48 hours. After that point, your body will have to rely on a different energy source in the form of fat and if your body isn’t effective at burning fat for fuel, this will likely lead to severe cravings especially for high carb foods.

Now, if you’ve trained your body to use fat for fuel by let's say following a low-carb diet, a keto diet or you've gone through long-duration fasting, then you won’t experience the same severity of hunger cravings. In fact, many people that fast frequently don’t experience hunger at all. This isn't only because their body is used to burning fat for fuel, but it's also because hunger levels increase at the times of the day that you normally eat. This is due to the hunger hormone ghrelin, which has the effect of stimulating your appetite when it's released. So during the first 24 hours that someone stops eating studies show that ghrelin will spike automatically for most people around the times of the day that they typically have breakfast, lunch, and dinner (1) and that spike will make you feel hungry. (1)

However, if you're someone that's already become accustomed to fasting every day, you won't experience these sharp spikes in ghrelin during your 16-hour fasting window, meaning you won't feel as hungry as someone that's used to more meals per day. (1) But even if you're used to breakfast, lunch, and dinner the data shows us that the spike in ghrelin is short-lived. if you just ride out the hungry feeling that you get, within about two hours from the initial spike in ghrelin, it should drop back down to normal levels and your appetite will drop down as well. 
Regardless after about the first 24 hours your body will burn through your remaining glycogen stores and switch almost entirely over to burning fat for fuel which will slowly lead to weight loss. Since your brain primarily relies on glucose to function your body will be able to separate...

[GravityTransformation]

References:

1. A 27-year-old male named Angus Barbieri once fasted for more than a year. Under supervision, he lived on multivitamins with yeast for 382 days. And he only drank water, coffee, tea, and diet soda.

2. He dropped his bodyweight from 456 pounds to 180 pounds in the process.

3. “Fasting improves cognition, stalls age-related cognitive decline, usually slows neurodegeneration, reduces brain damage”

4. Aslightly overweight but otherwise healthy man drank only water for 44 days.
“At the end of the fast, body mass had decreased by 25.5%, of which a quarter to a third was due to loss of fat and the remainder to fat-free mass, predominantly muscle.”

5. A man 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.

6. A woman had to go to the hospital after a 40-day water-only fast due to symptoms caused by a severe sodium deficiency.

7. Research shows that starvation increases the risk of infections, particularly malaria. Interestingly, sometimes, the body suppressed these infections during the fast but then only manifested upon refeeding.

8. The graph that’s at the top of this page shows growth hormone rising:

9. RIF attenuates inflammatory status of the body by suppressing proinflammatory cytokine expression

10. Ghrelin (the hunger hormone) automatically will spike during the times of the day that you're used to eating...typically during the regular times of breakfast, lunch and dinner. If you ignore the feeling of hunger within about 2 hours it should subside or at least dull the hunger.

11. Comparative Physiology of Fasting, Starvation, and Food Limitation (Graph)

12. hunter-gatherer anthropoids, including those living today, often eat intermittently depending upon food availability

13. According to a 2018 meta-analysis from the University of Glasgow there are no enhanced fat loss benefits from intermittent fasting. It is just as effective as regular continuous energy restriction ie. calorie-restricted dieting.
“Effect of intermittent energy restriction in comparison to continuous energy restriction revealed no significant difference in weight loss.”

14. This suggests that there are no special weight or fat loss benefits for intermittent fasting. This makes sense. After all, it's well-known that energy balance determines changes to the number on the scale.

[robertdunhill]

I'm eating once a week total now. I'm fat so think my body is feeding its self. Drinking loads of water. I don't feel hungry at all. It's getting harder and harder to get my self to eat. Am I really doing myself damage.
However my memory and retention for information has increased so much that i can do my job far better because I don't forget anything. All it took was me to stop eating. I wish I had done this through school I wouldn't have left without an education.

[cmwHisArtist]

When I was in my 20s I made up a diet called “eat what you want, but only one small thing, and only when VERY HUNGRY”.
When I felt pangs I would sip water, tea, or coffee until very hungry, and then would eat what I was in the mood for - an apple, a hamburger without the bun, a salad, a pudding. The first day I ate six times, next day four, normal became two, until at one point I realized I hadn’t eaten for two days because I hadn’t gotten hungry. Several things happened;
1. I found I was in the mood for something different each time and ended up eating a balanced diet.
2. My body really liked only having to digest only one thing at a time and my energy soared.
3. After a couple of days my stomach cavity shrank and I was full from less and less food.
4. I lost my carb addiction and 17 pounds in two months.
5. I found out my sinus congestion was only when I ate red meat. I stopped it for 7 years, and now can eat it a couple of times a week without getting stuffy.
6. I became really aware of what my body said it needed at different points of the day, and I cooperated.

[plasmasnake]

Back in september 2018, I discovered your channel, and followed your intermittent fasting tips. I was at 110kg at that time, with fast alone I was able to lose 30kg in a year with little training. To this day I'm still doing it, it allows me to control my weight, when I can't exercise for long periods, and I don't have to think about what I eat. It also helps my wallet too.

[Brvnkaerv]

I once went on a hungry strike. I lasted 5 days. Nobody cared. Then I took a vow of silence, and everybody cheered.

[avylonlightbringer]

I started Fasting every third day. So eat normal 2 days then nothing the 3rd. did this for about 8 months went from 273 down to 216 (57 lbs). Was a life changer. Haven't been able to continue due to cancer, but when I get back on me feet I will continue.

[mr.horseshoe]

I’ve been fasting for two months. Lost 50 pounds and I have so much energy now. And I don’t feel hungry at all. I have 100 more pounds to lose. I’ve been making sure to watch my electrolyte intake.

[nzmn]

I’ve been studying this stuff for years, and have never heard a more accurate, concise and practically communicated explanation. Bravo!

[SlowDelSol]

I’ve done 2-week fasts so far. Both great experiences and makes you see what your body is capable of. It’s not something you can recommend for everyone but it was great for me.

[robertrivera]

I'm on day 4 of a 5 day fast and I can honestly say the only negative effect I've experienced aside from hunger is heart palpitations. On a positive note I've lost 9 lbs, my mental clarity has increased and I feel like I'm in a better mood!

[fredbiscuit...]

An excellent video with very complex metabolic-processes explained in an easy-to-understand format. Well done GT :)

[Makise]

This was very informative and was exactly what I was looking for so thank you for making this video. I love all the amount of detail you went into with this and the step by step process of what happens to your body during it.

[citytucker]

I’ve been working out 2 years. IF worked it down to 23/1. I’m currently on day 3 of a water fast. Aiming for a week. It’s def easier than I thought. It’s all in your head.

[jarinorvanto]

Just postponing the breakfast during weekends a couple of hours feels good, and I have lost weight. I've never been overweight though. I have also reduced the number of meals / snacks during the weekends by one, making it a very light form of intermittent fasting. It was easy and gave results from the first day; I could feel the metabolism switch. I have however always eaten well; the difference is a reduction of what's not so healthy and also the number of meals by one during weekends. I don't have any cravings at all. Knowing what's bad for your health, effectively precludes such consumption. But I do allow myself goodies, such as desserts sometimes; but always make sure to enjoy these in conjunction with a meal, not as a snack in between.

[majorpaiyne]

YouTube has suggested I try and watch something out of my comfort zone and I clicked the link. It brought me here. Ironically this video is pretty much what i needed to see. I'm contemplating on extending Ramadan for myself in an effort to try and lose weight. I found this info to be very informative. Thank you for sharing!

[SetAside]

I thoroughly enjoyed the graphics in this video. and of course the content too. Thank you! Well done.

[ratatat]

Watched a lot of these videos and this is one of the best. Keeping it relatively simple but still very informative along with using great graphics gets the info across without being overwhelming.

[coachTaher]

Your diet is a bank account. Good food choices are good investments.

[chrishogg]

Dude this video is killer!
Easily one of the best science-based fasting tutorials Ive ever seen.
Fasting is an amazing tool that literally anyone can use to heal their body.
Three meals a day is a myth.

[brucewallagainsttheodds]

Thank you for spreading this information & being so detailed. Really helps 💪🏾💪🏾💪🏾