Intermittent Fasting & Hunger – What the Science says


Intermittent fasting has gotten a lot of attention
nowadays as there’s so many benefits to be had from it. It helps you lose weight, helps you gain muscle
and enhances your cognitive performance. Specifically, it lowers insulin- the fat storing
hormone involved with diabetes, it raises human growth hormone which does everything
from increasing muscle mass to making you look better and live longer, and it promotes
the release of brain derived neurotrophic factor, a key hormone for growing new brain
cells. Intermittent fasting is simple, all you do
is not eat for 16 hours of the day. But this is a radical idea for most people
considering we’re encouraged to be eating all the time, being told things like “breakfast
is the most important meal of the day” and “you need to eat six small meals to lose
weight.” Unsurprisingly hunger is the number 1 concern
when it comes to fasting. So, let’s take a look at how hunger works
so we can better deal with it. As Tim Russ said, “We often fear what we
do not understand; our best defense is knowledge.” The first thing you should know is that hunger
is not a simple equation of no food plus time equals more and more hunger. In a very thorough series on fasting in his
blog called “Intensive Dietary Management,” Dr. Jason Fung points to a study that shows
that while subjects went over 3 days without any food, the hunger hormone ghrelin gradually
but continually decreased. He says: “This means that patients were
far LESS hungry despite not having eaten for the past 3 days. This jives perfectly with our clinical experience
with patients undergoing extended fasting. They all expect to be ravenously hungry, but
actually find that their hunger completely disappears. ” This is because hunger is regulated by hormones
like ghrelin and it comes in waves. You do not get progressively hungrier the
longer you go without food- your body adapts to your REGULAR eating schedule. It knows when you usually eat, so it comes
to expect food and make you hungry around the same time each day. Here’s a study from the Medical University
of Vienna done on subjects participating in a 33 hour fast. Despite the early morning being when people
have gone the longest without food, ghrelin was the lowest. And, their ghrelin didn’t rise more and
more the longer they went without food- ghrelin rose at their normal eating times. And, it fell back down even though they didn’t
eat anything. So when you start fasting, it’s important
to know that hunger will arise and it is uncomfortable, but it will come and go. After a couple days, your hormones will adapt
to your new eating times and you will be less and less hungry until it’s no longer an
issue. This is why many people say that the first
4 days are the hardest. Un-adapting and re-adapting your eating times
is uncomfortable, but your body is very good at it. I’ve been doing intermittent fasting with
an eating window of 2 to 4 hours for the past year, and when I was first experimenting with
fasting, I actually tried eating once every other day. To my surprise, after only about 6 days of
this, I wasn’t that hungry on the no eating day. But, like clockwork, I started to get pretty
hungry on the eating day right around the usual time I would eat. Another very interesting thing about this
hormone ghrelin, is that it may be making you hungry in order to get you to take in
more salt. It would be very important to have a hunger
for salt as salt has many very critical functions: It’s needed by the heart to pump blood properly,
and it’s a key component in cell-to-cell communication and the optimal transmission
of nerve impulses to and from organs like the heart and brain. Low salt has been shown to stunt growth, increase
insulin resistance and increase uric acid levels, stimulating oxidative stress in the
mitochondria and weight gain. Despite all this, the standard low sodium
guidelines of only 2.3g of sodium per day drastically underestimate how much salt the
body really requires for optimal functioning. A study in the New England Journal of medicine
found that an estimated sodium intake between at least 3g and 6g per day was associated
with a lower risk of death and cardiovascular events. In fact, actually following the low salt guidelines
posed a particularly high risk to health. And, Intermittent fasting may have you requiring
even more salt than usual. Intermittent fasting lowers your insulin levels. This is great, and is one of the main goals
of intermittent fasting, but it’s often overlooked that insulin retains sodium, so
the lower your insulin goes, the more sodium your kidneys secrete. Losing a lot of sodium and other minerals
can leave you feeling sluggish and hungry. Now, your body really doesn’t want to lose
too much sodium, so one thing it does is it actually increases insulin levels in an attempt
to retain more sodium. A 1991 study done on 147 people found that
a low salt diet significantly increased serum insulin in these people. Of course higher insulin is something you
don’t want, so let me explain more about insulin and how it affects hunger. So when you eat, insulin goes up and, insulin
helps you utilize carbohydrate for energy or stores it as glycogen, which is basically
linked chains of glucose. This glycogen is stored in the liver or muscle. And when you have too much glycogen, the incoming
carbohydrate will be stored as fat. Now, different foods will give you a different
insulin rise, fat stimulates insulin a minimal amount while fiberless carbs provoke massive
rises in insulin. But the point is, insulin’s job is to help
you absorb and store nutrients. Next, after about four to six hours after
you eat, insulin levels will have gone down, and the glucose level in your blood starts
to decrease, this prompts the pancreas to secrete glucagon. Glucagon has almost the opposite function
of insulin. Insulin stores food energy, but glucagon pulls
that energy out from your glycogen stores and your fat stores. So if you’re eating every two hours and
getting six small meals a day, you never let glucagon do its job and your body never starts
burning into your glycogen or your fat stores. Not a good strategy for losing weight. Well what about hunger? Well, let’s look at this study from 1986. They found that if you inject an animal with
insulin, it will eat more. Adding insulin increases appetite. If you have insulin floating around with no
new glucose coming in, your blood glucose will drop, but insulin needs to be low for
glucagon to use your fat or glycogen stores for energy. With high insulin, you have no access to your
stored energy. So it makes sense for extra insulin to promote
hunger as the only way you can get new energy is to eat it and raise your blood glucose. And as you might expect, giving an animal
glucagon, reduced food intake. So glucagon is decreasing appetite. Now they also infused glucose into the animal’s
small intestine and it reduced food intake, so it’s of course not the case that carbs
don’t satiate you to some extent. But if you’re eating every two hours, you’re
constantly pumping out insulin and the levels never go low enough for glucagon to do its
job. This explains why you can eat a bowl of cereal
for breakfast or a huge plate of pasta for lunch and be hungry in just an hour or two. Refined carbohydrates like that will cause
the body to overshoot with its insulin secretion, so even after all the carbohydrates are processed
after the meal, you still have a bunch of insulin sitting around making you hungry. This overshooting with insulin also explains
why if you binge eat at night, you’ll wake up starving in the morning. So after a meal, if you’re patient, glucagon
will allow you to start running on your stored energy and you will be less hungry. So while fasting, glucagon suppresses hunger
and is helping you power the body by burning your stored glycogen and fat. Then when you run out of glycogen, you’re
burning primarily fat for energy and your body enters the state of ketosis. This produces a lot of ketone bodies, which
your body and brain will use for fuel. It’s a common misconception that the brain
runs only on glucose. In 1967, George Cahill found that the brain
will derive 2/3rds of its energy from ketone bodies made from fat. Though, some processes in the body still require
glucose, but you don’t need to eat that glucose – your body makes its own glucose
from things like glycerol and lactate. This is called gluconeogenesis. Earlier we saw that high glucagon and low
ghrelin during fasting will keep hunger in check. But, we can add ketone bodies to the list. There is data that show that ketone bodies
like beta hydroxybutyrate also reduce appetite. Which isn’t a surprise considering they
act as an energy source for the body. This is one of the reasons why a ketogenic
or low carbohydrate diet has such great synergy with intermittent fasting. These diets will keep insulin low, and allow
you to more use fat for energy, just like fasting will. So, if you’re able, I’d recommend trying
to shift your diet to one that is high in good fat, high in fiber, high in micronutrients,
moderate on protein and low in carbohydrate. You could even start eating like this before
you begin intermittent fasting and you’ll already be adapted to be getting your energy
from fat so you’ll have less hunger and adapt to intermittent fasting easier. You might be wondering why I said moderate
protein. Many people assume a low carb or keto diet
must have a lot of protein in it, but that’s not quite the case. Insulin is necessary for protein to be metabolized,
so you get some insulin rise when you eat protein. But not only that, when you eat more protein
than your body needs to make or repair cells, the excess will be broken down into glucose
through gluconeogenesis. In fact, diabetics have been shown to have
a 30% decrease in daily blood glucose levels just by restricting protein. Now there’s one last interesting thing about
insulin and hunger – it’s how it interacts with leptin, the satiety hormone. Essentially when you eat food, depending on
the composition of the meal, your levels of leptin go up and you feel more satiated. But, when you have too much insulin, it reduces
leptin signalling- your brain can’t pick up on the leptin signal, keeping you hungry. In fact, obesity which is virtually always
accompanied by insulin resistance is also accompanied by leptin resistance. If you want to stay satiated and full of energy
rather than be hungry and lethargic, you need to keep your insulin low. Lucky for you, fasting seems to be the best
way to lower insulin. So while intermittent fasting is hard for
the first couple of days, it’s helpful to know that your body and hormones are working
in your favor, making it easier and easier. And, if you get enough salt and minerals,
and eat high fiber, moderate protein and low carbohydrate then you can make the whole process
smoother.

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Reader Comments

  1. Pfsif

    I use to hate eating breakfast but the "experts" insisted not only to eat the "most important" meal of the day but to eat more smaller meals. WTF?

  2. LOVE LIGHT

    that's all great but I can't fall asleep i think you might have to kill me to make me fall asleep hungry cuz i don't see any other way to falla sleep hungry

  3. AquaHolicsUK

    So true. For those who are doubting this, easy way to find out is, try it for a month or two. It will be hard initially, once you're over that barrier, the results will speak for themselves.

    It's basically going against everything you have learnt to this point.

    By cutting out sugars, animal protein, fastfoods, junk foods you will start a "new you".

  4. Brendan Alexander

    I started 16:8 intermittent fasting plan 3 days ago. When I got to the eating window on the second day, I went to my favorite taco restaurant with the attitude "give it to me baby." I was astounded that I could barely eat half the tacos I usually do. My stomach got full very fast. This makes me think that one of the reasons you lose weight is because your stomach shrinks.

  5. Chandramouli Srinivasan

    Hunger is just caused by a hormone…It just comes and dissipates…Iam in Intermittent Fasting …very easy to follow..First few days Hunger hormone Ghrelin will tempt you to eat or munch something…As you practices this hormone vanishes during fasting time…You will get used to Intermittent fasting ..

  6. Michal Valta

    That bit about "too much protein" is nonsense. Not only was it proven in studies… And proven by countless carnivores around the world… But you are also ignoring most of human history…

  7. Pepe

    Very easy:
    You sleep ~8 hours and skip breakfast. You already fasted 12 hours. 50% of the day. Skip lunch as wel and you have fasted for about 16 hours (66% of a day). 16 hour fasts are easy.

  8. CBR600RR

    I tried keto and plateaued. I then went with counting calories and included carbs, and voila! I got past my palteau. You only need to consistently restrict calories by 500 from your BMR. That's all.

  9. kiso키소

    here in korea it’s common for people to go on water fasts, and it can help you lose up to 3 pounds a day when drinking a gallon of water,, the first time i did it, the hunger hit me for the first two days, but the second time i was only hungry the first day. if you want results, hunger comes with it

  10. sovereign775

    I learned in my harvard med school class that a high protein meal will actually result in a small increase in insulin and a greater release of glucagon. I'll try to look up where the professor got this research.

  11. jose soto

    I eat my last n only meal between 9
    and 10 I get up for work at 4:30 am. I drink some water first thing in the morning every morning. It’s like warming your car before u drive off. I’ll have a black coffee after that and then I won’t eat anything until 12:30 and it’s usually some roasted peanuts a cliff bar something very light. But the longer I go without the food the better I feel. Sometimes I’ll go to 8 9 and I’m not hungry and I feel great. I’m trimming down with ease.

  12. salvaged wretch

    one huge aspect of this I've noticed is, not having to think about what I'm going to eat all the time, when you IF or even fast for a few days worrying about food is a non issue.

  13. A D

    @What I've Learned, Sodium and salt aren't the same thing so recommending a low/no sodium diet is perfect a no-salt diet on the other hand my cause the effects you described.

  14. Pixel Pirate

    For me intermittent fasting has become a byproduct of doing keto. I just don't really feel hungry until the end of the day now, so I basically have a couple of coffees through the day then have a meal in the evening.

  15. Brittney Davis

    My mom told me that her grandmother told her when she is hungry put a little salt on your wrist to stop the hunger. My question is how did they know about all this stuff long ago. I'm sure if you told them about grelin the hunger hormone they would not even understand. It's really something that's all I'm saying.

  16. 4Fab Kids

    Just remember the body is super dynamic meaning it wants to be healthy but you have to do the work! When u r not eating your body will produce energy for itself through the break down of fat, so you won’t need to eat constantly!

  17. nazellina

    Ok. That is soooooo contrintuitive, so I need your help explaining smth to me.
    When I eat 3 times a day – it's the usuall. But when I might not eat for the whole day and have a dinner in the evening – that is a disaster! I eat, and eat, and eat and can't stop, because I feel no fullness. But if I've eaten 1-2 times more that day – that never happened. That is such an awfull feeling, that I try not to skip my meals at all, beacause that inevitable monstrosity Great Hunger will come and I won't be able to cope with it.

    Question 2: through the day it's usually not the hunger, that bothers me but weakness and dizziness in my head (like I'm gonna faint). Around the lunch time I feel so exhausted and have absolutely no energy to do my job and I feel how I need that glucose for my brain to be able to go another half of my working day.
    My job is an absolute brain work and I cannot imagine how my body could extract enough glucose from fat fast enough (glicogen that is stored in the liver is used up very fast in our bodies).
    I just can't afford thinking slowly and being like drunk because of lack of an energy!

    Can somebody help explaining this thing one more time on my example? Thanks!

    P.S. And what to do with a gym?! I can literaly faint when I'm training and not eated recently. How do you have energy to properly train?!

  18. Xandra J

    This is with the understanding that the body is processing and using insulin properly. What about those who are diabetic or have hormone dysfunction that causes insulin resistance? Can fasting still be beneficial?

  19. John Snow

    From my experience, a ketogenic diet is potentially very dangerous. There is just not enough known about it, especially for long-term. So be careful to not promote half-known facts.

  20. Dblood85

    Finally a damn video that’s easy to understand and with correct information. Not one of these videos that’s trying to sell one of their programs.

  21. Shawn Warnick

    Hold your beer? Who eats for 8 hours a day? Why dont they just say eating one meal a day instead of not eating for 16 hours of the day

  22. Swaghetti Yologness

    I am probably not getting an answer but can you eat only like 2 days of the week and run "on an empty tank" for the rest of it or will that affect you negatively?

  23. Ariko Subumo

    "Don't eat. It will make you healthy, free from ailments and save money. It will make you live longer." — Kim Jung-on, Dear Leader of North Korea

  24. devilish cat

    i do the the 16/8 fasting and really works for me i don’t feel hungry so often i don’t feel sluggish i don’t feel sleepy i’m more focus and energetic and i loose weight easily simply because i easily get full because my stomach adjust to the fasting

  25. ReasonableRadio

    can't we just control these levels? Why do we have to do it by starving when they're just simple chemicals? Why are real diet pills a myth lol

  26. Ashley

    I’ve been fasting during a 16 hour period but with school starting soon would I have to stop that?
    I want to know if skipping breakfast in the morning would harm me considering I have school and eating only during that 8 hour period I’m at school isn’t the most efficient

  27. Stream of Consciousness

    I fast every few days because I'm poor, I'm also obviously a genius. Food is poison and air is delicious, according to the video.

  28. T Pink

    How would one do this with a highly physical job though? I burn calories SO fast that if I don't eat every 2 hours, I have zero energy to continue my work.

  29. Ashley ASHLEYM

    I always notice I'm a lot hungrier when I'm not doing IF compared to when I am, When I am doing IF I'm almost never hungry and the only reason I still eat is because logically I know my body needs fuel to survive and nutrients to function properly.

  30. Rubén Alvarado Barzuna

    Hello. Thanks for an interesting video. I have two questions: how many meals should you have during your eating hours? How many calories should you consume (less, more, or as much as in conventional diets)?

  31. mp7925

    Khm, ghrelin or not, I had to eat every 3 hours years ago, when I needed to be away for i.e. 6+ hours, my last meal included a lot of eggs and cheese. That kept me hunger free for all that time. No ghrelin involved. And now that I'm on keto, I start to feel hunger usually something like 7-12 hours after last meal, independently when i had time to eat. Otherwise I agree with findings.

  32. Brenna Caldwell

    Thanks for the video! I've been tracking my food intake and macros, and i discovered I wasn't even getting close to the 2,300mcg of salt! Every time I tried IF, i would give in at the 14 hr mark despite quitting sugar. Now I know im not a weirdo for eating pickles at midnight. Thanks!

  33. Bakgethi Remote

    I was absorbing this and learning a lot, UNTIL, I saw the half-naked fat guy being hit by canon – now I can't watch the rest of the video because I keep rewinding to 2:26. LOL

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