Restricting Eating to a 12-Hour
Window of Time Each Day May Be Key to Healthy Weight
January 30, 2015
Story at-a-glance
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Intermittent fasting, which focuses on restricting
your eating to a small time window, can have a
beneficial effect on a wide array of biological
functions and systems
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Time-restricted eating can both prevent and reverse
obesity and related metabolic dysfunction
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Mice restricted to eating within an eight-, nine-,
or 12-hour window remained thin and healthy, even
when cheating on weekends, and/or eating a
high-sugar diet
By Dr. Mercola
Intermittent fasting can provide many important health benefits,
from improving your insulin/leptin sensitivity to helping your body
more effectively burn fat for fuel. It’s one of the most effective
ways I’ve found to shed excess weight for these two reasons.
That notion is held up by recent research published in the
journal Cell Metabolism,1
in which researchers concluded that time-restricted eating not only
prevented but also reversed obesity and related metabolic
dysfunction.
Even more remarkably, this was true even when the diet was less
than ideal. Time-restricted eating is my personal favorite of the
many intermittent fasting schedules available.
I believe it can be very helpful for those in need of shedding a
few extra pounds and/or who have insulin and leptin resistance—which
is the majority of the American population.
The reason so many struggle with their weight (aside from eating
processed foods that have been grossly altered from their natural
state) is because they’re in continuous feast mode and rarely ever
go without a meal.
As a result, their bodies have adapted to burning sugar as its
primary fuel, which down-regulates the enzymes that utilize and burn
stored fat. Fasting is an excellent way to “reboot” your metabolism
so your body can start burning fat as its primary fuel, which will
help you shed your unwanted fat stores.
Once your insulin resistance improves and you are normal weight
you can start eating more frequently, as by then you will have
reestablished your body’s ability to burn fat for fuel—that’s the
key to sustained weight management.
Intermittent Fasting as a Therapeutic Intervention
To assess the effectiveness of different time-restricted feeding
schedules on weight and metabolic function, the researchers2
divided adult male mice into four groups, each of which was fed a
specific diet:
- High-fat diet
- High-fructose diet
- High-fat and high-fructose diet
- Regular mouse kibble
In each of these four diet groups, half of the mice were allowed
to eat whenever they wanted during waking hours (ad libitum), while
the other half only had access to food during a restricted period of
time of eight, nine, 12, or 15 hours per day.
The experiment lasted for 38 weeks. At the end, the mice that ate
at all hours had become obese and suffered with metabolic
dysfunctions, while the mice restricted to eating within an eight-,
nine-, or 12-hour window remained thin and healthy.
This was true even for select groups of mice that were permitted
to cheat on weekends, and eat any time they wanted. Mice that were
switched from an ad libitum schedule to a restricted eating schedule
midway through the experiment also shed some of the excess weight
they’d accumulated. As reported by The New York Times:3
“Time-restricted eating didn’t just prevent but also
reversed obesity,’ says Satchidananda Panda, an associate
professor at the Salk Institute who oversaw the studies. ‘That
was exciting to see’... Precisely how a time-based eating
pattern staved off weight gain and illness is not fully
understood, but Dr. Panda and his colleagues believe that the
time at which food is eaten influences a body’s internal
clock. ‘Meal times have more effect on circadian rhythm than
dark and light cycles,’ Dr. Panda says. And circadian rhythm in
turn affects the function of many genes in the body that are
known to involve metabolism.”
Mini-Fasting—The 5:2 Plan
Another intermittent fasting schedule is the
5:2 Plan as popularized by
Dr. Michael Mosley and his FAST diet. Here, you’re allowed to
eat normally five days a week and only fast on two. On fasting days,
you restrict your eating to 600 calories or less for men, and 500
calories or less for women. This kind of restricted eating plan has
been shown to have similar effects and benefits as continuous modest
calorie restriction, which includes weight loss, improved insulin
sensitivity, and improvements in other biomarkers for health. In
some cases it may even be more effective.
As reported by NPR:4
“A study5
by researchers at the University of Manchester found that when
overweight women followed a 5:2 approach, they lost more weight
and body fat and improved their insulin resistance compared with
women who followed a more traditional diet of limiting calories
seven days per week One explanation for the success of the 5-2
dieters could be that a day of mini-fasting can lead to a
diminished appetite...There may be an evolutionary explanation
for this because humans (and other animals) have fasted
intermittently for much of our time on Earth, after all. As a
recent paper6
in the Proceedings of the National Academy of Sciences notes,
"The most common eating pattern in modern societies, three meals
plus snacks every day, is abnormal from an evolutionary
perspective.”
How and Why Intermittent Fasting Works
Again and again, researchers have concluded that fasting—which
includes not only eating less food overall, but also eating less
frequently—can have a beneficial effect on a wide array of
biological functions and systems. One 2013 review7
found a broad range of therapeutic potential of intermittent
fasting, even when total calorie intake per day did not change, or
was only slightly reduced. Studies included in the review produced
evidence that intermittent fasting may:
Limit inflammation |
Improve circulating glucose and lipid levels |
Reduce blood pressure |
Improve metabolic efficiency and body composition,
including significant reductions in body weight in obese
individuals |
Reduce LDL and total cholesterol levels |
Help prevent type 2 diabetes, as well as slow its
progression |
Reverse type 2 diabetes |
Improve pancreatic function |
Improve insulin levels and insulin sensitivity |
Reproduce some of the cardiovascular benefits
associated with physical exercise |
Protect against cardiovascular disease |
Modulate levels of dangerous visceral fat |
As noted above, one of the reasons for these health benefits
relate to the fact that the human body appears to be designed to
thrive in a cycle of “feast and famine.” By imitating the ancestral
conditions of cyclical nourishment, your body enters into a state of
optimal functioning. Three major mechanisms by which fasting benefit
your health include:
- Increased insulin sensitivity and mitochondrial
energy efficiency – Fasting increases insulin
sensitivity along with mitochondrial energy efficiency, and
thereby retards aging and disease, which are typically
associated with loss of insulin sensitivity and declined
mitochondrial energy.
- Reduced oxidative stress – Fasting
decreases the accumulation of oxidative radicals in the cell,
and thereby prevents oxidative damage to cellular proteins,
lipids, and nucleic acids associated with aging and disease.
- Increased capacity to resist stress, disease and
aging – Fasting induces a cellular stress response
(similar to that induced by exercise) in which cells up-regulate
the expression of genes that increase the capacity to cope with
stress and resist disease and aging.
Who Might Benefit from Exercising on an Empty Stomach, and Why?
The cyclical availability of food in ancient times also meant
that our ancestors had to engage in physical activities, sometimes
strenuous, without having anything to eat first. Modern research now
confirms that this, too, has biological benefits, and that our
obsession with keeping our bellies full at all times—especially if
we’re about to do physical work—may not be the ideal approach for
all people all the time. As noted in a previous Huffington Post8
article:
“It's an ongoing debate within the world of fitness:
should you eat
breakfast before exercising in the morning, and are there
any benefits to working out on an empty stomach? ‘It all depends
on what type of training you are going to do and for what
purpose,’ says John Rowley, Wellness Director for the
International Sports Science Association (ISSA)... The main
advantage to exercising on an empty stomach: the potential to
burn more fat...
[E]xercisers with weight loss goals might find an
advantage in waking up and exercising first thing in the morning
before eating breakfast or fasting for a few hours before a
mid-day or evening workout. ‘The less glucose you have in your
system the more fat you will burn,’ says Rowley. However, if
your goals are performance related (e.g. to improve strength or
speed), working out without fueling up probably isn't your best
bet because a lack of available energy might prevent you from
putting forth your best effort.”
Intermittent Fasting and High-Intensity Exercise Is a Potent Combo
for Weight Loss
When it comes to shedding unwanted pounds and reworking your
fat-to-muscle ratio,
high-intensity interval training (HIIT) combined with
intermittent fasting is a winning combination that’s hard to
beat. When you combine these two strategies, especially if you
exercise in a fasted state, it effectively forces your body to shed
fat because your body's fat burning processes are activated by
exercise and lack of food. The good news is that you don’t have to
keep on intermittently fasting forever if it doesn’t appeal to you
long-term. Also if you are already your ideal weight, then there
really isn’t much need to exercise fasting as it will limit your
performance.
If you need to lose 50 pounds, you’re looking at about six months
or so of intermittent fasting, after which you can revert back to
eating more regularly. My only caveat is that you also need to pay
attention to the quality of the food you eat. Since both HIIT and
intermittent fasting help shift your body from burning sugar to
burning fat as its primary fuel, it’s important to feed your body
the right nutrients. Even on non-fasting days, I believe it’s
important to eat a diet that is:
- High in healthy fats and very low in fructose and
other sugars. Those with insulin and leptin resistance
will likely benefit from getting 50-85 percent of their daily
calories in the form of healthy fat from avocados, organic
grass-fed butter, pastured egg yolks, coconut oil, and
raw nuts such as macadamia, pecans, and pine nuts.
Avoid processed foods as most are very high in fructose and
other health-harming ingredients, including harmful trans fats.
If you’re insulin/leptin resistant (and/or have high blood
pressure, high cholesterol, diabetes, heart disease, or are
overweight), you’d be wise to limit your total fructose
consumption to 15 grams per day. For all others, the recommended
daily allowance of fructose is 25 grams per day for optimal
health.
- Moderate amounts of high-quality protein
from organically raised, grass-fed or pastured animals. Most
will likely not need more than one gram of protein per pound of
lean body weight, which for most people would equate to
somewhere in the neighborhood of 40-80 grams of protein per day.
If you’re pregnant or exercising intensely, you would need about
25 percent more.
- Unrestricted amounts of fresh vegetables,
ideally organic.
Making these dietary shifts, and adding two or three weekly
sessions of high intensity exercises is, I believe, a solid strategy
for reaching your weight loss and fitness goals. Also, if you’re
hesitant to try fasting for fear you’ll be ravenously hungry all the
time, you’ll be pleased to know that intermittent fasting will
virtually eliminate hunger and sugar cravings.
Sure, it may take a few days or even weeks, but once your body
shifts into burning fat for fuel rather than sugar, the sugar
cravings will be a thing of the past. I’m a fellow of the American
College of Nutrition and have studied nutrition for over 30 years,
and I’d never personally encountered or experienced hunger cravings
just disappearing like they did when I implemented intermittent
fasting!
A tool that can be helpful to keep you on track with your
intermittent fasting schedule is the Emotional Freedom Techniques
(EFT). In the following video, Julie Schiffman demonstrates how to
tap for emotional components that can crop up whenever you’re trying
to make a dietary change.
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