The Complete Guide to Fasting: A Special Interview With Dr. Jason Fung
Fasting is one of the oldest
dietary interventions in the world, and modern science confirms it can
have a profoundly beneficial influence on your health. Dr. Jason Fung, a
nephrologist (kidney specialist) with a practice in Canada, has
written an important landmark book on this topic.
"The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting,"
co-authored with Jimmy Moore, details how to implement fasting and
overcome some of the most common challenges that might arise, including
persistent fears and myths associated with extended water fasting.
For the first decade of his practice, Fung was — like most doctors —
conventionally oriented. As a kidney specialist, many of his patients
had type 2 diabetes as the primary cause of their kidney failure.
It became clear to him that the conventional treatment of type 2 diabetes was seriously flawed.
Despite patients' best efforts to manage their diabetes,
taking their insulin and following the recommended diet and so on,
they would still end up with complications such as kidney disease,
requiring dialysis, or they'd need amputations, or they'd go blind.
"As a doctor, we got trained to give medications, but obviously it wasn't working," he says.
"The answer is actually pretty obvious. Because if diabetes, type 2
predominantly, is what's causing the kidney disease, you're not going to
be able to do anything about the kidney disease until you get rid of
the diabetes.
That was kind of where I started. Then I thought, 'Everybody says
type 2 diabetes is this chronic kind of progressive disease … It only
goes forward, one way.' But actually when you think about it, type 2
diabetes isn't like that at all …
[I]f you want to get rid of the type 2 diabetes, you have to get
rid of the obesity … That's how you're going to help people get better.
I started thinking about what causes weight gain … It's certainly not
calories. That's our big mistake. That's why we've been unsuccessful at
creating weight loss, because we've got the wrong kind of target …
It's really about the hormonal balance and predominantly about
insulin. We have to reduce insulin. Low-carbohydrate diets are a way to
lower insulin … In some people, that'll reverse their diabetes …
I started using low-carbohydrate diets and it didn't really work.
The problem was that it was a little complicated for people …
I had to make it simpler … I thought, 'Why not fasting?' … It's
been used for thousands of years … I started looking at some of the
science … There are actually huge benefits that we weren't recognizing.
Part of it was also we've always been trained, 'You have to eat.
You have to eat.' But in fact, that's not true. If you think about it,
in the old days … there would be lots of days where people didn't eat …
That's really what [body] fat is [for]. It's really simply stored
fuel; stored food energy. We're using it [when we fast]. That's it.
That's all that happens. There's no serious side effects or consequences
to fasting.
If there was, we would have known about it several thousand years ago. But there wasn't. That's where I started from."
Fung went on to implement fasting in his practice, and the results, he
says, have been "unbelievable." He's been able to take many patients
off all medications; they're losing weight, report increased energy,
and their diabetes is reversed.
"This is why we go into medicine: To make people better. For the
first time, this was what was happening. Before, for 10 years, all I
did was watch people get worse until I put them on dialysis. That was
really not the way to go," he says.
When he first sought to implement this program clinically, there was no
formal guide to follow, which is what inspired him to write "The Complete Guide to Fasting." Using his own clinical experience, he created a guide that anyone can use to their benefit.
"When people start, they're super skeptical. They think it's [a]
terrible [idea]. But then they come back and they're total converts.
They're like, 'This is the best thing.'
Because they're losing weight, they're seeing that their
medications are going down, their sugars are going down. It's obvious
to them that they're actually getting much, much healthier," he says.
"This is all without medications. We're trying to take away
medications. It's an all-natural solution. You're really letting your
body just clean itself out from all of that excess sugar and fat.
There's nothing wrong with that. It's free. It's available. All we
have to do is give people the knowledge and they can make themselves
better, which is incredible."
If you're obese, nutritional ketosis is another excellent dietary
protocol. I recently interviewed Dr. Jeanne Drisko, head of the
University of Kansas Integrative Medical Center, who has used a ketogenic protocol in a clinical setting for many years now.
The challenge is implementation and compliance. Nutritional ketosis is
more complicated than fasting. Fasting can also be a more rapid
process. Rather than waiting weeks or months for your body to
upregulate and be able to effectively metabolize fat again, fasting
really jumpstarts this process.
Fung's book is so helpful because it provides easy-to-follow basic
guidelines for fasting, and reviews some of the most common myths and
fears that keep many from implementing a fasting regimen.
One common myth is that fasting will lead to loss of muscle mass. The
book clearly describes the process of protein catabolism, explaining
how your body actually downregulates protein catabolism and upregulates
growth hormones in response to fasting.
"If you follow the biochemistry, your body stores energy as
glycogen in the liver, which is links or chains of sugar, and then it
stores [it as] body fat.
During fasting, you start by burning off all the glycogen in the
liver, which is all the sugar. There's a point there where some of the
excess amino acids in your body need to get burnt as well.
That's where people say, 'That's where you're burning muscle.'
That's not actually what happens. The body never upregulates its
protein catabolism. Never is it burning muscle; there's a normal
turnover that goes on.
There is a certain amount of protein that you need for a regular
turnover. When you start fasting, that starts to go down and then fat
oxidation goes way up. In essence, what you've done is you switched over
from burning sugar to burning fat. Once you start burning fat, there's
almost an unlimited amount of calories there. You could go for days
and days.
What's interesting is that if you take a pound of fat, that's
roughly 3,500 calories. If you eat somewhere around 1,800 to 2,000
calories a day, it takes two full days of fasting to burn a single
pound of fat, which is very surprising to people. If you're trying to
lose 100 pounds, you could theoretically go 200 days of fasting just to
burn all that fat … People worry about fasting for 24 hours. I'm like,
'You could go 200 days.' Then it's like, 'OK. Maybe it's OK to go 24
hours without eating.'"
Another common fear is that fasting equals starvation, which is not
true. First of all, starvation is a forced situation that you have no
control over whereas fasting is optional. You have complete control.
Many also believe they cannot or should not fast because it will send
their body into "starvation mode" — a situation where the body starts
holding on to fat rather than burning it off.
"What they're talking about is where the body's metabolism starts
to slow down so significantly that instead of burning 2,000 calories a
day, your body might burn 1,000 calories a day. In that case, even if
you're eating only 1,500 calories a day, for example, you're going to
gain your weight back. That's actually what happens when you reduce
your calories. We know that … as you cut your calorie intake, your
calorie expenditure goes down as well.
Starvation mode actually is guaranteed if you just try and cut your
calories. But what's interesting is that fasting doesn't do that. What
happens during fasting is that … after four days of fasting, the basal
metabolic rate is actually 10 percent higher than when you started. The
body has not shut down at all. In fact, what it's done is it switched
fuel sources. It switched from burning food to burning [body] fat. Once
it's burning [body] fat, it's like, 'Hey, there's plenty of this
stuff. Let's burn our 2,000 calories'…"
This is also why fasting tends to increase energy opposed to leaving
you feeling drained. If you're overweight and lethargic, fasting helps
unlock all that energy already lodged in your body that you previously
had no access to. Fasting forces your body to start accessing those
stores of energy, and once that happens, your body suddenly has a near
unlimited supply of energy!
Fasting also helps improve other biochemical systems in your body.
There's interplay of hormonal systems like the mammalian target of
rapamycin (mTOR), AMPK, leptin and IGF-1 — all of which are optimized
in the right direction when fasting. It also improves your mitochondrial
function, allowing your mitochondria to regenerate. So it's not just
simply turning on an enzyme switch to burn fat; it's a very complex
process that upregulates in the direction of health.
Insulin is the primary hormone that tells your body whether to store
energy or burn it. When you eat, you're taking calories in and insulin
goes up. Higher levels of insulin signal your body to store energy.
When insulin falls, it tells your body to release energy. When you
develop insulin resistance, your insulin levels remain chronically
elevated, hence your body is in constant fat-storing mode.
Without the signal to burn energy, you end up feeling tired and
sluggish. You have plenty of fuel available, but it's all "locked away"
in your fat cells, and it will remain unavailable until your body
receives the appropriate signal — a drop in insulin. This is also why
it's so difficult to lose weight when you are insulin resistant.
The key to breaking this cycle is to have sustained low insulin for
periods of time, and this is why fasting can be so tremendously
beneficial. Fasting lowers insulin more powerfully than any other
strategy, which then allows the stored energy (body fat) to be used
again.
"That's why you start to use up some of your fat stores and you're
not hungry, because you're, in essence, eating your own fat. That's the
other thing that people are always surprised about. When they come
back, they say, 'Hey, I'm not actually that hungry.' I'm like, 'That's
no surprise, because your body is burning fat. If it's burning [body]
fat, it doesn't need to eat," Fung explains.
"We talk a lot about what you should eat and what you shouldn't
eat. But people never talk about meal timing — making sure you have
long periods where you're not eating. Look at the word "breakfast" in
English. That's break fast. That's the meal that breaks your fast. That
implies two things: One, fasting is a part of everyday life. We've
forgotten that. We think it's some sort of Herculean effort, but it's
not. We should be fasting every day.
If you balance your periods of feeding and fasting, you will stay
in balance. If you are always in feeding phase, then you're not going
to be in balance and you're going to gain weight. The second thing it
means is that you can break your fast at any time. It doesn't have to
be 8:00 in the morning. You can break your fast at any time of the day
or you can eat two days later.
It's not that important … People, even when they're not hungry, are
forcing themselves to eat something … Forcing yourself to eat when
you're not hungry is not a winning strategy for weight loss. Logically,
it doesn't make sense. But these sort of illogical thoughts get
propagated and then it becomes conventional dietary advice."
There are many ways to do an extended fast. Following are some of the most common variations: • Water fasting. This
is exactly what it sounds like: You don't eat; you only drink water,
for several days in a row (typically no less than 24 hours). • Water plus non-caloric beverages.
A slight variation on the water fast is to include other non-caloric
beverages, such as herbal tea and coffee (without milk, sugar or other
sweetener, including artificial non-caloric sweeteners). • Bone broth variation.
Another variation Fung often recommends for longer fasts is to allow
the use of bone broth. In addition to healthy fats, bone broth also
contains lots of protein, so it's not really a true fast. Still, in his clinical experience, many who take bone broth in
addition to water, tea and coffee experience good results. "If you're
getting the results you want and it's making it easier for you to stick
to the program, then you should do it," he says. "If you start getting
bad results with fat fasting or bone broth fasting, you can go to
classic water-only fast." • Fat fasting. Here,
you allow healthy fats during the fast in addition to water and/or
non-caloric beverages. While you probably would not eat a stick of
butter, you could have bulletproof coffee (black coffee with butter, coconut oil or MCT oil), for example. Alternatively, you could add the fat to your tea. Dietary fat produces a very minor insulin response, and since you're
keeping your insulin levels low, you're still getting most of the
benefits of fasting even though you're consuming plenty of calories.
Adding healthy fats such as butter, coconut oil, MCT oil and avocado
can make the fasting experience a lot easier. "Lots of people have done
very well with this sort of fat fast," Fung notes, adding "Anything
that increases your probability of success I'm all for."
I'm personally quite intrigued with the fat fast. I recommended water
fasting to my landscaper, but after three days she felt really
fatigued. While this is a normal response in the initial stages, I made
her a "fat-bomb drink," which perked her right back up. I use Pau
d'arco tea as the base. It contains beta-lapachone, which upregulates NAD+, an important
electron transfer mechanism and mitochondrial signaling molecule. To
that, I add some coconut oil, MCT C8 oil, butter and a little stevia.
It contains about 400 or 500 calories per cup.
Part of the key is to avoid protein to inhibit mTOR. While the level of
protein at which you'll counteract the benefits of fasting is
individual, Fung believes you'll likely see results as long as you stay
below 10 or 20 grams of protein per day. As a reminder, protein raises
your insulin, although not to the same degree as net carbs do. Excess
protein is likely more damaging metabolically than excess carbs.
"I was looking at some data recently where they graphed where your
blood sugars are in relation to where your ketones are. Ketones start
to go up as your blood glucose falls [but] that slope changes in
different people," Fung says. "If you look at, for instance,
type 2 diabetics, they have a very steep slope. That is their blood
glucose — even as it falls — ketones don't go up.
That's probably why they feel like crap, because they're not
getting the ketones. The blood glucose is going down, which it should,
but the body should be producing ketones for their fuel for the brain,
but it's not. In those cases, some of the fat bombs, some of the
exogenous ketones, may actually make it a lot easier for people to get
through that. As your body becomes [fat] adapted, which can take two
weeks to a month, that shouldn't happen anymore …
If you have never fasted and you do a three-day fast, you may feel
pretty lousy. We tell people to expect that. You can either continue or
you can take a break and let your body become more adapted to it."
The same applies to hunger pangs, which tend to kick in the hardest on
the second day of a fast. By the fifth or sixth day, however, hunger
practically disappears.
While 80 percent of the population would likely benefit from water
fasting, there are several absolute contraindications. If any of the
following apply to you, you should NOT do extended types of fasting:
If you're on medication, you need to use caution when fasting, as some
may need to be taken with food. This includes metformin, aspirin and
any other drugs that might cause stomach upset or stomach ulcers. Risks
are especially high if you're on diabetic medication. If you take the
same dose of medication but don't eat, you run the risk of having very
low blood sugars (hypoglycemia), which can be very dangerous.
So, if you're on diabetic drugs, you must adjust your medication before
you fast. If your doctor is adverse toward or unfamiliar with fasting,
you'd be wise to find one that has some experience in this area so
that they can guide you on how to do this safely.
Keep in mind that hypoglycemia is best diagnosed by symptoms alone,
opposed to any specific blood glucose number. I wear a 24-hour
continuous glucose monitor. Sometimes when I'm really pushing my carbs
low, I'll go down to 35 milligrams per deciliter (mg/dl) at night, yet
I'm not symptomatic at all. For someone who's hypoglycemic or used to
having blood sugar levels of 180, dropping to 35 could put them in
serious trouble.
Also be aware that if you have high uric acid, fasting can precipitate gout.
Fasting tends to increase your uric acid level because your kidneys
increase their reabsorption of uric acid when you don't eat. Most
people will not experience a problem, but if you have gout you may need
to consult with your physician about this.
Your body is a marvel of ingenuity, and the more you can work WITH it
rather than against it, the healthier you're likely to be. Consider the
following: Intermittent fasting
involves scheduling your meals in such a way that you get a period of
fasting each day. Typically, you'll eat all of your meals within a six-
or seven-hour window. When I first started intermittent fasting, I
decided to skip breakfast.
However, in studying mitochondrial function, I realized it's not a good
idea to eat late at night, because that's when your body is readying
for rest, regeneration and repair. Eating in the evening creates
surplus ATP, which will simply generate excessive amounts of damaging
reactive oxygen species (ROS). At that point, I began avoiding food for a
minimum of three hours (and typically it's closer to five or even six
hours) before bedtime.
"There's some interesting data on that," Fung says. "If you
look at insulin response, insulin drives a lot of weight gain. But if
you take the same meal close to bedtime versus in the middle of the
day, you actually get a higher insulin response at the end of the day,
which is interesting and which is not good.
I actually think it's best to take your biggest meal sometime
[around] lunch to early afternoon, and then go easy at [your] night
time meal and into the next day. I think there's something in that …
There's not a lot of science out there, but I think it really makes a
lot of sense. In terms of the advantages of fasting, the key thing to
understand is that fasting is almost the opposite of every diet that's
out there. That's why it's so successful.
There are so many advantages to it: It's not complicating your
life. It's actually simplifying your life. It doesn't cost any money. In
fact, this saves you money. It doesn't take any time. In fact, it
saves you time because you don't have to cook, you don't have to eat,
you don't have to do anything. You don't have to plan for it.
There are so many different ways that it's beneficial. You can add
it to any diet. If you're vegetarian, you can still fast. If you don't
eat nuts, if you have an allergy to meat, if you can't cook, you can
still fast. Any diet can be improved by fasting. It's so powerful. You
can continue fasting as long as you want until you get the benefits
that you want. The world record is 382 days. You can go a long time
powered on your own body fat."
Barring you fall into any of the contraindicated groups, fasting is
safe. Even very sick patients have done it and improved their health in
the process. Fung has been using water fasting and variations thereof
in his clinical practice for the past five years.
In that time, he's placed well over 1,000 patients on various fasting
regimens. Some do tremendously well. One man in his mid-50s had
struggled with diabetes for two decades. Within two weeks, he was able
to quit taking all of his diabetes medications. His blood sugar was back
to normal without them.
"Then his sister saw he was doing really well. She comes in. She's
on three pills for diabetes. Within a month, we took her off all three.
She takes herself off the other two blood pressure medications and
cholesterol pills. We took her off six medications in a month and a
half. That's amazing. Obviously, they did very well. But that just goes
to show you what can happen when you try some of these things," Fung says.
"Initially, there was a huge amount of skepticism. Everybody
thought I was crazy. But now I have so much support from my own local
area because everybody has seen the results. I have lots of doctors at
my hospital who are doing it. Once they see it themselves, they're like
… 'This is amazing.' They start referring me patients and say, 'I want
these benefits for my patients.'
Because they know they can't provide that kind of supportive
environment that we can provide; that we set up in our clinic, where we
kind of anticipate their problems, give them the support, the online
resources, the books … to be able to do it successfully. That's the key:
To have the acceptance. There are so many naysayers out there who say,
'You shouldn't do this. You can't do this.' But within my own local
area now, we're really seeing a lot of strong support for this, because
it's undeniable."
I believe Fung has written an excellent, if not the best, book on how
to implement extended fasting. If you're overweight or struggle with
chronic illness, I highly recommend getting "The Complete Guide to Fasting,"
as it will really guide you through the process. Most likely — unless
you're taking medications — you will not require a professional
healthcare consultant help you. It's nice to have, but you can likely
manage on your own.
You can also learn more by visiting Fung's website, IntensiveDietaryManagement.com. It has a weekly blog and provides a lot of information about fasting and related topics. Another helpful website is DietDoctor.com, where you can find plenty of information about intermittent fasting. Fung is a contributor to this site as well.
"The most important message, I suppose, is that health is really
yours to take back, to take back from all the drug pushers and the
people who just want you to take medications and who tell you that you
can't do it and you'll always have type 2 diabetes," Fung says.
"The solutions are all there. It's all within your grasp. It just
requires the right knowledge … As physicians, the 19th to 20th century
is all about drugs because we had a lot of infections. That was a great
model. You take those antibiotics, you get better.
But now as we go onto the 21st century, it's all metabolic
diseases. They're all dietary diseases. The problem is we're trying to
use drugs for dietary diseases. Then we wonder why our drugs are no
good. It's because the premise is entirely wrong. It's like bringing a
snorkel to a bicycle race. It's just the wrong thing. We've got to move
on." Fasting Helps Reverse Diabetes — And Related Health Conditions
The Clinical Use of Fasting
Breaking Down Myths About Fasting
The 'Starvation Mode' Myth
Understanding the Role of Insulin
Variations of Fasting
Important Contraindications
Use Caution If You're on Medication
Interesting Facts About Fasting and Meal Timing
Yes, Fasting Is Safe and, Yes, You Can Do It
More Information
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