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.

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