What the Science Says About Intermittent Fasting
June 28, 2013
Story at-a-glance
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It's long been known that calorie restriction can increase
the lifespan of certain animals. More recent research
suggests that intermittent fasting can provide the same
health benefits as constant calorie restriction, which may
be helpful for those who cannot successfully reduce their
everyday calorie intake
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“Undernutrition without malnutrition” is the only
experimental approach that consistently improves survival in
animals with cancer, and extends overall lifespan by about
30 percent
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Both intermittent fasting and continuous calorie restriction
have been shown to produce weight loss and improve metabolic
disease risk markers. However, intermittent fasting tends to
be slightly more effective for reducing insulin resistance
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Besides turning you into an efficient fat burner,
intermittent fasting can also boost your level of human
growth hormone (aka the “fitness hormone”) production by as
much as 1,200 percent for women and 2,000 percent for men
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Intermittent fasting can improve brain function by boosting
production of the protein BDNF, which activates brain stem
cells to convert into new neurons and triggers other
chemicals that promote neural health. This protein also
protects your brain cells from changes associated with
Alzheimer’s and Parkinson’s disease, and helps protect your
neuro-muscular system from degradation
By Dr. Mercola
Is it a good idea to “starve” yourself just a little bit
each day, or a couple of days a week? Mounting evidence
indicates that yes, intermittent fasting (IF) could have a
very beneficial impact on your health and longevity.
I believe it’s one of the most powerful interventions out
there if you’re struggling with your weight and related
health issues. One of the primary reasons for this is
because it helps shift your body from burning sugar/carbs to
burning fat as its primary fuel.
As discussed in the featured article,1
intermittent fasting is not about binge eating
followed by starvation, or any other extreme form of
dieting. Rather what we’re talking about here involves
timing your meals to allow for regular periods of
fasting.
I prefer daily intermittent fasting, but you could also
fast a couple of days a week if you prefer, or every other
day. There are many different
variations.
To be effective, in the case of daily intermittent
fasting, the length of your fast must be at least eight
hours long. This means eating only between the hours of 11am
until 7pm, as an example. Essentially, this equates to
simply
skipping breakfast, and making lunch your first meal of
the day instead.
You can restrict it even further — down to six, four, or
even two hours if you want, but you can still reap many of
these rewards by limiting your eating to an eight-hour
window each day.
This is because it takes about six to eight hours for your
body to metabolize your glycogen stores; after that you
start to shift to burning fat. However, if you are
replenishing your glycogen by eating every eight hours (or
sooner), you make it far more difficult for your body to use
your fat stores as fuel.
Intermittent Fasting — More a Lifestyle Than a Diet
I have been experimenting with different types of
scheduled eating for the past two years and currently
restrict my eating to a 6- to 7-hour window each day. While
you’re not required to restrict the amount of food you eat
when on this type of daily scheduled eating plan, I would
caution against versions of intermittent fasting that gives
you free reign to eat all the junk food you want when not
fasting, as this seems awfully counterproductive.
Also, according to research published in 2010,2
intermittent fasting with compensatory overeating did not
improve survival rates nor delay prostate tumor growth in
mice. Essentially, by gorging on non-fasting days, the
health benefits of fasting can easily be lost. If so, then
what’s the point?
I view intermittent fasting as a lifestyle, not a diet,
and that includes making healthy food choices whenever you
do eat. Also, proper nutrition becomes even more important
when fasting, so you really want to address your food
choices before you try fasting.
This includes minimizing carbs and replacing them with
healthful fats, like coconut oil, olive oil, olives, butter,
eggs, avocados, and nuts. It typically takes several weeks
to shift to fat burning mode, but once you do, your cravings
for unhealthy foods and carbs will automatically disappear.
This is because you’re now actually able to burn your stored
fat and don’t have to rely on new fast-burning carbs for
fuel. Unfortunately, despite mounting evidence, many health
practitioners are still reluctant to prescribe fasting to
their patients. According to Brad Pilon, author of Eat
Stop Eat:3
“Health care practitioners across the board are
so afraid to recommend eating less because of the stigma
involved in that recommendation, but we are more than
happy to recommend that someone start going to the gym.
If all I said was you need to get to the gym and start
eating healthier, no one would have a problem with it.
When the message is not only should you eat less, you
could probably go without eating for 24 hours once or
twice a week, suddenly it’s heresy.”
The Health Benefits of Intermittent Fasting
Aside from removing your cravings for sugar and snack
foods and turning you into an efficient fat-burning machine,
thereby making it far easier to maintain a healthy body
weight, modern science has confirmed there are many other
good reasons to fast intermittently. For example, research
presented at the 2011 annual scientific sessions of the
American College of Cardiology in New Orleans4
showed that fasting triggered a 1,300 percent rise of human
growth hormone (HGH) in women, and an astounding 2,000
percent in men.
HGH, human growth hormone, commonly referred to as "the
fitness hormone," plays an important role in maintaining
health, fitness and longevity, including promotion of muscle
growth, and boosting fat loss by revving up your metabolism.
The fact that it helps build muscle while simultaneously
promoting fat loss explains why HGH helps you lose weight
without sacrificing muscle mass, and why even athletes can
benefit from the practice (as long as they don't overtrain
and are careful about their nutrition). The only other thing
that can compete in terms of dramatically
boosting HGH levels is high-intensity interval training.
Other health benefits of intermittent fasting include:
Normalizing your insulin and leptin sensitivity,
which is key for optimal health |
Improving biomarkers of disease |
Normalizing ghrelin levels, also known as "the
hunger hormone" |
Reducing inflammation and lessening free radical
damage |
Lowering triglyceride levels |
Preserving memory functioning and learning |
Intermittent Fasting Is as Good or Better Than Continuous
Calorie Restriction
According to Dr. Stephen Freedland, associate professor
of urology and pathology at the Duke University Medical
Center, “undernutrition without malnutrition” is the only
experimental approach that consistently improves survival in
animals with cancer, as well as extends lifespan overall by
as much as 30 percent.5
Interestingly enough, intermittent fasting appears to
provide nearly identical health benefits without being as
difficult to implement and maintain. It’s easier for most
people to simply restrict their eating to a narrow window of
time each day, opposed to dramatically decreasing their
overall daily calorie intake.
Mark Mattson, senior investigator for the National
Institute on Aging, which is part of the US National
Institutes of Health (NIH), has researched the health
benefits of intermittent fasting, as well as the benefits of
calorie restriction. According to Mattson,6
there are several theories to explain why fasting works:
"The one that we've studied a lot, and designed
experiments to test, is the hypothesis that during the
fasting period, cells are under a mild stress, and they
respond to the stress adaptively by enhancing their
ability to cope with stress and, maybe, to resist
disease... There is considerable similarity between how
cells respond to the stress of exercise and how cells
respond to intermittent fasting.”
In one of his studies,7
overweight adults with moderate asthma lost eight percent of
their body weight by cutting their calorie intake by 80
percent on alternate days for eight weeks. Markers of
oxidative stress and inflammation also decreased, and
asthma-related symptoms improved, along with several
quality-of-life indicators.
More recently, Mattson and colleagues compared the
effectiveness of intermittent fasting against continuous
calorie restriction for weight loss, insulin sensitivity and
other metabolic disease risk markers. The study, published
in the International Journal of Obesity in 2011,8
found that intermittent fasting was as effective as
continuous calorie restriction for improving all of these
issues, and slightly better for reducing insulin
resistance. According to the authors:
“Both groups experienced comparable reductions in
leptin, free androgen index, high-sensitivity C-reactive
protein, total and LDL cholesterol, triglycerides, blood
pressure and increases in sex hormone binding globulin,
IGF binding proteins 1 and 2. Reductions in fasting
insulin and insulin resistance were modest in both
groups, but greater with IER [intermittent fasting] than
with CER [continuous energy restriction].”
How Intermittent Fasting Benefits Your Brain
Your brain can also benefit from intermittent fasting. As
reported in the featured article:
“Mattson has also researched the protective
benefits of fasting to neurons. If you don't eat for
10–16 hours, your body will go to its fat stores for
energy, and fatty acids called ketones will be released
into the bloodstream. This has been shown to protect
memory and learning functionality, says Mattson, as well
as slow disease processes in the brain.”
Besides releasing ketones as a byproduct of burning fat,
intermittent fasting also affects brain function by boosting
production of a protein called brain-derived neurotrophic
factor (BDNF). Mattson’s research suggests that fasting
every other day (restricting your meal on fasting days to
about 600 calories), tends to boost BDNF by anywhere from 50
to 400 percent,9
depending on the brain region. BDNF activates brain stem
cells to convert into new neurons, and triggers numerous
other chemicals that promote neural health. This protein
also protects your brain cells from changes associated with
Alzheimer’s and Parkinson’s disease.
BDNF also expresses itself in the neuro-muscular system
where it protects neuro-motors from degradation. (The
neuromotor is the most critical element in your muscle.
Without the neuromotor, your muscle is like an engine
without ignition. Neuro-motor degradation is part of the
process that explains age-related muscle atrophy.) So BDNF
is actively involved in both your muscles and your
brain, and this cross-connection, if you will, appears to be
a major part of the explanation for why a physical workout
can have such a beneficial impact on your brain tissue — and
why the combination of
intermittent fasting with high intensity exercise
appears to be a particularly potent combination.
Give Intermittent Fasting a Try
If you’re ready to give intermittent fasting a try,
consider skipping breakfast, make sure you stop eating and
drinking anything but water three hours before you go to
sleep, and restrict your eating to an 8-hour (or less) time
frame every day. In the 6-8 hours that you do eat, have
healthy protein, minimize your carbs like pasta, bread, and
potatoes and exchange them for healthful fats like butter,
eggs, avocado, coconut oil, olive oil and nuts — essentially
the very fats the media and “experts” tell you to avoid.
This will help shift you from carb burning to fat burning
mode. Once your body has made this shift, it is nothing
short of magical as your cravings for sweets, and food in
general, rapidly normalizes and your desire for sweets and
junk food radically decreases if not disappears entirely.
Remember it takes a few weeks, and you have to do it
gradually, but once you succeed and switch to fat burning
mode, you'll be easily able to fast for 18 hours and not
feel hungry. The “hunger” most people feel is actually
cravings for sugar, and these will disappear, as if by
magic, once you successfully shift over to burning fat
instead.
Another phenomenal side effect/benefit that occurs is
that you will radically improve the beneficial bacteria in
your gut. Supporting healthy gut bacteria, which actually
outnumber your cells 10 to one, is one of the most important
things you can do to improve your immune system so you won’t
get sick, or get coughs, colds and flus. You will sleep
better, have more energy, have increased mental clarity and
concentrate better. Essentially every aspect of your health
will improve as your gut flora becomes balanced.
Based on my own phenomenal experience with intermittent
fasting, I believe it’s one of the most powerful ways to
shift your body into fat burning mode and improve a wide
variety of biomarkers for disease. The effects can be
further magnified by exercising while in a fasted state. For
more information on that, please see my previous article
High-Intensity Interval Training and Intermittent Fasting -
A Winning Combo.
Clearly, it’s another powerful tool in your box to help
you and your family take control of your health, and an
excellent way to take your fitness to the next level.
© Copyright 1997-2013 Dr. Joseph Mercola. All Rights Reserved.
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