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
selected. 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
hunger. 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 Experiment. 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 restriction. 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
soup. ” 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. Ghrelin, known as the “hunger hormone”
has been found to increase appetite and weight gain. A study at the Medical University of Vienna
looked at patients participating in a 33 hour fast. Their ghrelin levels were checked every 20
minutes. 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
time. 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 fasted. 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 hunger. 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 up. “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 nothing. 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 sparer.” “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 mass. 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.


  1. What I've Learned

    June 23, 2017 at 7:04 am

    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. Shlomo Taitz

    November 1, 2019 at 7:32 am

    Pertinent info, excellently explained.

  3. Pierre Nodoyuna

    November 2, 2019 at 12:27 pm

    Is there any difference in muscle loss between a skinny person and a very muscular one when fasting?

Leave a Reply