Fasting vs. Eating Less: What’s the Difference? (Science of Fasting)

Fasting vs. Eating Less: What’s the Difference? (Science of Fasting)

“Breakfast of champions.”
What’s the difference between eating less
food and eating no food?
Well, Let’s look at two different situations.
…In 1944, a study called the Minnesota Starvation
Experiment was conducted and was designed
to understand the effects of caloric restriction
on the body in order to gain some knowledge
that would help people starving in the aftermath
of World War 2.
Thirty-six healthy men with an average height
of 178cm (about five foot ten) and average
weight of 69.3 kilograms (or 153 pounds) were
For three months, they ate a diet of 3200
calories per day.
Then, for six months they ate only 1570 calories.
However, caloric intake was adjusted to attempt
to have the men lose 1.1 kilograms per week,
meaning some men got less than 1000 calories
per day.
The foods given were high in carbohydrates-
things like potatoes, turnips, bread and macaroni.
Meat and dairy products were rarely given.
During the six months, the men experienced
profound physical and psychological changes.
Everyone complained that they were too cold.
One subject talked about having to wear a
sweater in July on a sunny day.
The subjects’ body temperature dropped to
an average of 95.8 degrees Fahrenheit (35.4
degrees celsius).
Physical endurance dropped by half, and strength
showed a 21 percent decrease.
The men experienced a complete lack of interest
in everything except for food, which they
were obsessed with.
They were plagued with constant and intense
There were several cases of neurotic behavior
like hoarding cookbooks and utensils.
Two participants had to be cut from the experiment
because they admitted to stealing and eating
several raw turnips and taking scraps of food
from garbage cans.
At first, the participants were allowed to
chew gum, until some of the men began chewing
up to 40 packages a day.
Now compare all this to the case of Angus
Barbieri, a Scottish man who in 1965 fasted
for over 380 days straight.
That is he took in no food whatsoever -nothing
but water, black coffee and straight tea for
just over a year.
He lost 276 pounds, going from from 456 pounds
to 180.
A case report published by the Dundee University
Department of Medicine in 1973 said “…the
patient remained symptom-free, felt well and
walked about normally,” and “Prolonged
fasting in this patient had no ill-effects.”
There were no complaints of mind numbing hunger
and he kept the weight off- for several years
his weight stayed around 196 pounds.
This of course is not a perfect comparison,
with the case of Angus, there’s only one
subject and his starting weight was drastically
higher compared to those in the Minnesota
However, it does illustrate some very interesting
points about just how different of a physiological
response you get from fasting (that is, eating
nothing) compared to eating less, or caloric
Dr. Jason Fung, a Toronto physician specializing
in kidney disease, and author of the Obesity
Code, says that compared to fasting, Caloric
Reduction will result in: less weight loss,
more lean mass loss (i.e. more muscle loss),
and more hunger.
Let’s start by talking about hunger.
In Upton Sinclair’s 1911 book “The Fasting
Cure,” he writes about fasting as a means
to improve health.
In describing his first couple attempts at
fasting he writes “I was very hungry for
the first day-the unwholesome, ravening sort
of hunger that all dyspeptics know.
I had a little hunger the second morning,
and thereafter, to my great astonishment,
no hunger whatever-no more interest in food
than if I had ever known the taste of it.”
Sinclair recommends to do quite long fasts
– around 12 days or so.
In a section addressing concerns about fasting
he writes “Several people have asked me
if it would not be better for them to eat
very lightly instead of fasting, or to content
themselves with fasts of two or three days
at frequent intervals.
My reply to that is that I find it very much
harder to do that, because all the trouble
in the fast occurs during the first two or
three days.
It is during those days that you are hungry.”
Then he says: “…perhaps, it might be a
good thing to eat very lightly of fruit, instead
of taking an absolute fast-the only trouble
is that I cannot do it.
Again and again I have tried, but always with
the same result: the light meals are just
enough to keep me ravenously hungry…”
In the book he says you will know when you
should finish fasting, because your hunger
will “return.”
He quotes a letter he received from a 72 year
old man saying “After fasting twenty-eight
days I began to be hungry, and broke my fast
with a little grape juice, followed the next
day with tomatoes, and later with vegetable

He quotes several other letters he received
from readers and this disappearance and reappearance
of hunger is a common theme.
Everyone who wrote to him fasted for at least
10 days, saying they only broke their fast
when hunger “returned.”
This phenomenon runs contrary to the idea
one would get hungrier and hungrier as long
as they don’t eat.
However, most people have experienced for
themselves that this is not the case.
Some will find that they are not hungry at
all in the morning or at least they are not
as hungry as they are for lunch or dinner.
But unless you are eating in your sleep, the
morning is when you have gone the longest
without food.
Some of this can be explained by the hormone
Ghrelin, known as the “hunger hormone”
has been found to increase appetite and weight
A study at the Medical University of Vienna
looked at patients participating in a 33 hour
Their ghrelin levels were checked every 20
Here’s how the levels changed over time.
What’s interesting is ghrelin is lowest
at 9:00AM, which is when they have gone the
longest without eating.
And, Ghrelin comes in waves and overall doesn’t
rise during the period the subjects were fasting.
Then, As you can see, ghrelin rises in sync
with normal lunch and dinner times, as if
the body had learned to expect food at that
However, that ghrelin rise spontaneously decreases
after 2 hours without food.
I’ve experienced this kind of spontaneous
decrease in hunger myself many times when
I was working as a consultant.
Lunch time would come and I would be hungry,
but I was too busy to eat so I just kept working.
Pretty quickly I forgot about eating and wasn’t
particularly hungry until dinner time.
This is very helpful to keep in mind if you’re
doing a long fast or even if you’re starting
intermittent fasting – you’re going to get
annoying waves of hunger, especially around
the times that you usually eat.
But, it won’t get worse, the hunger will
simply go away if you are patient.
Another study concerning ghrelin was done
at Aarhus University Hospital in Denmark and
it shows what happens if you do a longer fast.
They looked at the ghrelin levels of 33 subjects
who fasted for 84 hours.
So, did they get increasingly hungrier throughout
the fasting period?
Well, No.
Their ghrelin followed similar rhythms each
day but actually decreased the longer they
Going longer without food actually made them
less hungry.
This gives credence to what Upton Sinclair
and his readers said about hunger disappearing
after the first 3 days of fasting.
I’ve done a couple 5 and 6 day fasts in
the past myself and this was indeed the case.
Actually, I did a 4 day fast last week and
again the 4th day was when I had the least
Another thing that may be contributing to
this phenomenon is that you are entering ketosis.
Ketosis is a physiological state where your
metabolism switches to using primarily fat
for energy.
For this reason ketosis is popular as a weight
loss method, but it has many other benefits
including better physical and mental efficiency.
Ketosis occurs when you restrict carbohydrates
down to 50 grams or less and you don’t eat
too much protein.
Everyone’s body is a bit different so you
might have to eat even less carbohydrate or
may have room for more, but the recommended
ratio of a ketogenic diet is to get 5% of
your calories from carbs, 25% from protein
and 75% from good fat.
A simpler way to enter ketosis is just don’t
eat anything for a long enough time.
This is one of the major points in the difference
between fasting and caloric restriction.
The problem with the subjects in the Minnesota
Starvation experiment was that they were eating
just enough to keep them out ketosis and keep
their metabolism primed for burning carbohydrate
(glucose), so they couldn’t use their body
fat for energy.
This explains a lot of things like why they
were losing their strength and were very sluggish
and cold.
It also clears up why Upton Sinclair said
fruit or light meals were just enough to keep
him ravenously hungry and far weaker than
if he had just eaten nothing.
As I explained in my last video, insulin is
necessary for glucose to get into the cell
to be used for energy.
When you eat carbohydrates, the pancreas secretes
insulin to deal with it and too much insulin
hampers the action of something called hormone
sensitive lipase which is necessary to mobilize
fat and use it for fuel.
Though, keep in mind that grains or refined
carbohydrates will provoke a much higher insulin
response than say green vegetables.
Now because the body is having a hard time
using its fat for fuel, it will do a couple
things: One, it will simply slow down metabolism
to preserve energy.
In the Minnesota Starvation experiment, the
subjects metabolism dropped by 40 percent.
Their bodies didn’t have access to its stored
energy, and their restricted calorie diets
don’t provide much fuel so there’s no
choice but to slow down the metabolism.
Ironically, in the case of fasting, as Jason
Fung points out – metabolism actually goes
“If you don’t do anything about your insulin
and just reduce your calories, your metabolism
goes down.
But what happens during fasting?
Well, here’s a study of 4 consecutive days
of fasting.
What happens to your REE – this is this middle
line here, that’s the resting energy expenditure.
It doesn’t go down, it goes up.
You’re burning more energy than you did.”
The other thing the body will do when it can’t
use fat for fuel is break down muscle into
glucose through a process called gluconeogenesis.
The body doesn’t want do this too much because
it’s not very smart to completely eat through
something as important as muscle, but when
it can’t access its own stored energy it’s
more likely to resort to this.
This is why you’ll experience more muscle
loss on caloric restriction than if you ate
When you are fasting, Human Growth Hormone
is released.
As the name implies, Human Growth Hormone
is an anabolic hormone – a hormone conducive
to growth.
In Leningher’s Principles of Biochemistry
textbook they give the example of how injecting
the human growth hormone gene into a mouse
makes it unusually large.
As explained in Guyton’s Textbook of Medical
Physiology: “…growth hormone also mobilizes
large quantities of free fatty acids from
the adipose tissue, and these in turn are
used to supply most of the energy for the
body cells, thus acting as a potent “protein
“That is human growth hormone is protecting
your muscles from breaking down.
The study I referred to earlier about subjects
undergoing an 84 hour fast shows that growth
hormone rises significantly after the second
day of fasting.
As mentioned earlier, you should enter ketosis
sometime within the first 3 days or so of
fasting, and it depends on how much you are
moving around and what your diet was like
before starting the fast.
The state of ketosis is a great indicator
that your body is making good use of its stored
body fat for energy.
In Tim Ferriss’ book “Tools of Titans,”
Tim talks about his first clinically supervised
7 day fast.
For some sort of liability reasons, he wasn’t
allowed to exercise or leave the facility.
Considering exercise is a potent stimulator
of human growth hormone and will help deplete
glucose stores, not getting any exercise is
a great way to prevent yourself from getting
into ketosis during a fast.
It’s also a great way to lose muscle.
Tim says he lost 12 pounds of muscle during
the overly restrictive clinically supervised
7 day fast.
But, when following a protocol designed to
get him into ketosis as soon as possible – involving
things like 4 hours of brisk walking, he did
a ten day fast and apparently lost zero muscle
One last factor in Ketosis preserving muscle
is leucine.
When you’re in ketosis, you have a higher
fasting blood leucine level.
And leucine is a key branch chain amino acid
that has an anabolic effect on the body so
it preserves lean body mass.
A lot of people interested in building muscle
may be worried that fasting or a ketogenic
diet wouldn’t work for them because insulin
and therefore carbohydrates are necessary
for protein synthesis (i.e. muscle growth),
but actually this leucine fills that role
and is a good trigger for protein synthesis.
So, just to sum all this up: compared to a
conventional calorie restricted diet, fasting
means you lose more weight in the form of
fat, you keep more muscle, you have more energy,
and you are less hungry . If proper weight
loss is your goal, it might be better to eat
nothing at all rather than eating a conventional
low calorie diet.

100 thoughts on “Fasting vs. Eating Less: What’s the Difference? (Science of Fasting)”

  1. Just in case I should also say that of course you need to balance fasting with eating – You need to survive off of something. I have been doing intermittent fasting the past year (22 hours fasted, 2 hours eating – you can widen it to 16/8, which still provides great benefits) and will fast for a couple days every other month or so. Several other people have recommend a routine like this – Tim Ferriss recommends doing a 3 day fast once per month and a 7 day fast once per year.

  2. I can't do fasting, I tried and I get huge migraines and really weak and then I can't take care of my kids.

  3. For me the move was to get off carbs, and get into ketosis, before starting to fast. Makes it much easier to get a fast going if you're already in ketosis.

  4. My body forced me into an intermittent fasting diet after overeating just about every day.
    I topped out at 330lbs before my new diet was forced upon me through nausea, now I'm 230lbs and last I checked I'm still dropping.
    I'd drop more i'd imagine if I started to exercise regularly but I kinda wanted to see what progress could be done without it.

  5. Been fasting for a year and a half and lost 25 pounds the first 2 months. Never felt better. I fast 19 hours a day and eat from 1pm to 6pm. Works for me

  6. When I eat breakfast I am always hungry again an hour or so later but when I don't I'm often not hungry until 2 or even later

  7. I can tell u since fasting I have no need for blood pressure pills!!! I am healthier my skin is glowing n firmer. It’s just awesome how I have more energy plus more time. Eating n preparing food takes up hours from our days, which we don’t notice soon as u r fasting u realize how much free time u have.

  8. It doesn't sound right to me though, starving your self, not exercising, no protein, fruits and vegetables that makes you even hungrier! I'm not saying that I disagree completely, I'm just skeptical about it. Although you have some great arguments and you've done your research! Well, I will keep searching

  9. Did my first fast for 24 hours a month ago. From that time on my common fasting rate is 20 hours a day. Doing my cardio and HIITs too, before having a meal. I was craving a lot before that but now I only have some cups of no-sugar tea or water when hunger starts to kick-in. If you do not use any medication and feel healthy, you may give it a try and who knows – you'd like it!


    i exercise ( i dont know how muay thai is classified as, intense and short? not intense and long? its one hour training ) three times a week, and im planning to start doing it everyday

    this idea has me interested, however im still in my teens and im worried it might affect my growth. and also am worried that i wont have sufficient energy and strength to train. during training, all the cardio ( THERES LOTS OF CARDIO ) and the punching and kicking, i dont feel strong enough, and i eat before training. ( however, ive only just started, so it might have to do with me not being conditioned)

    what im wondering is, have you, people who’ve fasted, practiced sports or fighting or cross fit? were you able to do it? how did you feel?

    note: i am concerned about my health, i do want to lose weight, but health is much more important, im wondering if there are studies that state LONG TERM health benefits, not just weight loss.

  11. Best and the most straightforward video of how to loose fat 👍.
    Thank you so much
    Love from India ❤️

  12. I do a 20:4 fast and I NEVER feel hungry. I just choose to eat after 20 hours so I don’t get a headache, but I feel so much more energized and lighter throughout the day. I’ve always skipped breakfast, even as a child. So getting to the 20:4 fast was easy for me. Now that I have a daughter, I am more mindful of my health. I want to live a long healthy life so she never has to worry about me! Thank you for this great information

  13. Fasting works. I've done 2 separate fast in my life because i would regain the weight once i stop. Now on my 3rd stint and works same as before.

  14. I'm doing a 16:8 fast. I have never felt this energetic in my whole life. Preparing my body to go a full water fast.

  15. I was dieting before I saw thos video. I am going to start fasting tomorrow. Hopefully I lose weight and it seems easier and healthier than dieting and restricting all of my calories.

  16. Serious question, how do you avoid getting ulcers and other gastro intestinal *sideffects due to skipping meals or fasting? We've been told that you can get ulcers by not eating

  17. For men who want to lose weight, the science is clear that intermittent fasting is the best way to do it. For women of reproductive age, intermittent fasting can wreak havoc on your hormones. If you notice, a lot of the examples and studies cited are on men.

  18. I started with keto diet. Less than 40gram of carbs. 3 meals a day.

    Then started to reduce the number of meals.
    2 meals a day
    1 meal a day.

    I'm now on 1 meal a day.
    Will be start fasting 4 days later.

  19. Fasting is for people who stay home and don't drive far distances to work. What if the person get dizzy while driving.

  20. I’ve been fasting and doing keto for a month now. 17 pounds down. Insulin and blood sugar are controlled. Skin is clearing up because my insulin levels are normal, I would have dark spots on my face and a dark neck because high insulin can damage your skin. Energy feels great. I’ll update on month 2

  21. I'm going to see how long I can last
    1stJuly- Pretty smooth sailing for the most part. I felt slightly hungry as I was walking most of the day. Took a 'nap' from 4-9pm but I started to really feel it around 11pm (the time I typically eat the unhealthiest.) Note that this increased hunger only lasted about an hour and I was back to the way I was before.

  22. What is fasting? I'm 80 and does drinking coffee with milk cancel your fast or any other drink. I'm in around 36 hrs of no food but I've been drinking liquids.well done to you all

  23. So diets are keeping us hungry, fat and preventing us from making muscle? Makes total sense and the health industry is a huge business

  24. How do you get enough calories and proteins (and all other stuff you need) in such a short windows of time ?
    I don’t need to lose weight (would even like to put on 2 or 3kg) but would like to experiment the benefit of fasting : clear mind, clean stomach, etc…

  25. Fasting every Monday and Thursday every week, from sunrise to sunset, then fasting for one full month every year.

    Don't forget shalat of course.

  26. Read Dr. Shelton’s books. Fasting means only water and no other drinks like tea, chewing gum, etc. Eating partially leads to starvation, meaning your body uses its nutrition reserves to digest partial foods, but when you fast with water, the body learns to use fat for energy. When fasting it is important to rest, stay warm and drink water per thirst. All living animals fast because they don’t find food every day, except for the two legged one, who eats 4-5 times a day.

  27. I am 18 and have no interest in food and eating . I just don't want to eat . I am 6'1 ,but skinny . There have been days I haven't ate just because nothing reminded me of eating …I just forgot food .

  28. For a month I’ve only eaten twice a day with LARGE gaps in between. I’m talking 8-12 hours. I had already lost 4 kg in 3 weeks

  29. i was an overweight 16 year old when i first got introduced to fasting. it was amazing when i lost a lot of the weight, but it became an unhealthy obsession. my brain equated starvation with success and happiness, marking the beginning of a 2 year battle with anorexia that i’m still fighting. while that isn’t the fastings fault, and it has been a very positive thing for many, i hope other young teens who are desperate to lose weight and are insecure about their bodies fast safely and don’t develop toxic mindsets. maybe not even fast at all, considering the study was done on adults.

  30. thanks for posting this, clear and concise! it has always seemed to be true that eating nothing is better than eating very little. it just means that being sober is not an option, but a requirement
    been a drunk for a while but never-ever considered lite beer.that seems like diet chocolate,why bother

  31. I’m 15 and have been intermittent fasting for 2 years except for a couple days where I ate normally once every fortnight.

    At first, fasting was real hard for me. I’d bring nothing to school but my hunger would force me to give into temptation and buy some lunch. (Btw, I don’t eat breakfast and only eat until I got home from school which is around 4-4:30)
    As I kept fasting, I’d find that my hunger would come in less fits and I can easily ignore it and find that my hunger would disappear completely for the rest of the day. This meant that I was slowly killing my appetite and after about a year of fasting, I found myself eating less than one meal a day as my appetite was basically gone. This was where I found that I became extremely drowsy and tired so I forced myself to eat more a day and regain my hunger. Now I’m back where I am with ‘normal’ rates of hunger and have about 1.5 meals a day with a lot of snacks.

    Today is the first day of my water fast for maybe 4 days? I’ve never tried full fasts before and dw I’ve done my research. I’ve cleared the first week of my school hols to just hibernating in bed, drinking plenty of water and basically just being a immobile potato for a couple days lol

    Next holiday I’m planning to go for a 7 day water fast :))

    Wish me luck 🤪

  32. Fasting = Healing, autophagy, weight loss, barely any metabolic side effect….

    Eat less = Restriction and starvation…

  33. Be careful when it comes time to eat after fasting- because the weight can come back like a boulder. Keep a tight watch on the scale as you eat. I suggest only small portions of eggs, spinach, walnuts and avocado.

  34. But ghrelin is a GHRH so what mechanism does the body use to maintain LBM after a long period of fasting?

  35. It’s not rocket science, go on 16/8 and lose weight, I have abs now, first time in 40 years. Stop stuffing your face with crap, take care of your brand.

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