Confirmed—Fructose Can Increase Your Hunger and Lead to Overeating
January 14, 2013
Story at-a-glance
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Scientists using fMRI tests have shown that fructose triggers
changes in your brain that may lead to overeating and weight
gain. When you drink a beverage containing fructose, your brain
does not register the feeling of being full, as it does when you
consume simple glucose
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Fructose is also metabolized to fat in your body far more
rapidly than any other sugar, and the metabolism of fructose by
your liver creates a long list of waste products and toxins,
including a large amount of uric acid, which drives up blood
pressure and can cause gout
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As a standard recommendation, I advise keeping your total
fructose consumption below 25 grams per day. For most people it
would also be wise to limit your fructose from fruit to 15 grams
or less
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According to a recent study, altering your typical eating
habits―such as getting up in the middle of the night for a
snack―causes a certain protein to desynchronize your internal
food clock, which can have a detrimental effect on your health
and well-being
By Dr. Mercola
People everywhere are finally waking up to the indisputable fact
that all sugars are not created equal when it comes to the
physical end results they create.
Scientists using newer functional magnetic resonance imaging
(fMRI) tests have now shown that fructose, a sugar found in most
processed foods (typically in the form of high fructose corn syrup),
can in fact trigger changes in your brain that may lead to
overeating and weight gain.1
The researchers discovered that when you drink a beverage
containing fructose, your brain does not register the feeling of
being satiated, as it does when you consume simple glucose. As
reported by Yahoo! Health:2
"All sugars are not equal — even though they contain the
same amount of calories — because they are metabolized
differently in the body.
Table sugar is sucrose, which is half fructose, half
glucose. High-fructose corn syrup is 55 percent fructose and 45
percent glucose. Some nutrition experts say this sweetener may
pose special risks, but others and the industry reject that
claim. And doctors say we eat too much sugar in all forms."
Beware: Fructose Can Make You Hungry, Study Finds
Twenty healthy adults were included in the featured study,
published in the journal JAMA on January 2.3
fMRI was used to measure the hypothalamus response when the
volunteers consumed a beverage containing identical amounts of
either fructose or glucose (75 grams). The two drinks were given in
random order to all participants during testing sessions spaced
eight months apart.
Your hypothalamus helps regulate hunger-related signals involving
a number of hormones, including insulin, leptin, and ghrelin. The
scans revealed that when drinking glucose, within 15 minutes the
activity in the area of the brain involved with reward and desire
for food was suppressed, which leads to a feeling of fullness or
satiety. According to co-author Dr. Robert Sherwin:4
"With fructose, we don't see those changes. As a result,
the desire to eat continues — it isn't turned off."
In fact, fructose not only did not suppress hypothalamic
activity, it actually caused a small spike instead. Furthermore,
glucose boosted the links between the hypothalamus, thalamus, and
striatum, while fructose strengthened the connectivity between the
hypothalamus and thalamus, but not the striatum. This is
important, as the striatum also deactivates once your body senses it
has eaten enough... According to the authors:
"These findings suggest that ingestion of glucose, but
not fructose, initiates a coordinated response between the
homeostatic-striatal network that regulates feeding behavior."
What all this means in everyday terms is that when you consume
fructose, you may actually be "programming" your body to consume
more calories, as fructose fails to trigger that feeling of
fullness, and may even trigger continued hunger pangs. Dr. Jonathan
Purnell, an endocrinologist at Oregon Health & Science University,
told Yahoo! Health:
"It implies that fructose, at least with regards to
promoting food intake and weight gain, is a bad actor compared
to glucose."
How Your Body Metabolizes Fructose Versus Glucose
Part of what makes fructose so unhealthy is that it is
metabolized by your liver to fat in far more rapidly than any
other sugar. The entire burden of metabolizing fructose falls on
your liver, and it promotes visceral fat.5
This is the type of fat that collects around your organs and in your
abdominal region and is associated with a greater risk of heart
disease.
Without getting into the complex biochemistry of carbohydrate
metabolism, it is important to understand how your body processes
fructose versus glucose.
Dr. Robert Lustig, Professor of Pediatrics in the Division of
Endocrinology at the University of California, has been a pioneer in
decoding sugar metabolism. His work has highlighted some major
differences in how different sugars are broken down and used. Here's
a summary of the main points:
- After eating fructose, 100 percent of the metabolic burden
rests on your liver. With glucose, your liver has to break down
only 20 percent. The metabolism of fructose by your liver
creates a long list of waste products and toxins, including a
large amount of uric acid, which drives up blood pressure and
causes gout.
- Every cell in your body, including your brain, utilizes
glucose. Therefore, much of it is "burned up" immediately after
you consume it. By contrast, fructose is turned into free fatty
acids (FFAs), VLDL (the damaging form of cholesterol), and
triglycerides, which get stored as fat.
- The fatty acids created during fructose metabolism
accumulate as fat droplets in your liver and skeletal muscle
tissues, causing insulin resistance and non-alcoholic fatty
liver disease (NAFLD).6
Insulin resistance progresses to metabolic syndrome and type II
diabetes.
- Fructose is the most lipophilic carbohydrate. In other
words, fructose converts to glycerol 3 phosphate (g-3-p), which
is directly used to turn FFAs into triglycerides. The more g-3-p
you have, the more fat you store. Glucose does not do this.
- When you eat 120 calories of glucose, less than one calorie
is stored as fat. 120 calories of fructose results in 40
calories being stored as fat.
- Glucose suppresses your hunger hormone ghrelin and
stimulates leptin, which suppresses your appetite. Fructose has
no effect on ghrelin and interferes with your brain's
communication with leptin, resulting in overeating.
Known Health Ramifications of a High-Fructose Diet
Consuming foods that contain high amounts of fructose—even if
it's a natural product—is, to put it bluntly, the fastest way to
trash your health. GreenMedInfo.com,7
has collated a number of scientific studies that have linked
fructose to about 30 different specific diseases and health
problems.
Adding insult to injury, HFCS is most often made from
genetically engineered corn, which is fraught with its own well
documented side effects and health concerns, from an increased risk
of developing food allergies to the risk of increased infertility in
future generations, and possibly cancer, according to a recent
lifetime feeding study. Select the hyperlinks provided to review
how fructose may:
My Recommended Fructose Allowance
With regards to the featured study findings, Scientific
American notes:8
"Could fructose consumption alone really be playing such
an outsized role in expanding our pant sizes? 'A common counter
argument is that it is the excess calories that are important,
not the food. Simply put: just eat less,' Purnell and Fair
noted. 'The reality, however, is that hunger and fullness are
major determinants of how much humans eat, just as thirst
determines how much humans drink.
These sensations cannot simply be willed away or
ignored.' In order to eat less (and consume fewer calories
overall), they argued, then, one should avoid foods or
ingredients that fail to satisfy hunger. And that, according to
the results from the new study, would mean those
fructose-sweetened foods—and drinks."
As a standard recommendation, I advise keeping your TOTAL
fructose consumption below 25 grams per day. For most
people it would also be wise to limit your fructose from fruit to
15 grams or less, as you're virtually guaranteed to
consume "hidden" sources of fructose if you drink beverages other
than water and eat processed food.
Fifteen grams of fructose is not much -- it represents two
bananas, one-third cup of raisins, or two Medjool dates. Remember,
the average 12-ounce can of
soda contains 40 grams of sugar, at least half of which is
fructose, so one can of soda alone would exceed your daily
allotment.
In his book, The Sugar Fix,
Dr. Richard Johnson includes detailed tables showing the content
of fructose in different foods -- an information base that isn't
readily available when you're trying to find out exactly how much
fructose is in various foods. I encourage you to pick up a copy of
this excellent resource. You can find an abbreviated listing of the
fructose content of common fruits in this previous article.
How Fructose Affects Your "Fat Switch"
Dr. Johnson has also authored another book that is of major
importance to anyone who has ever struggled with their weight and/or
persistent health issues. According to Dr. Johnson, based on his
decades of research:
"Those of us who are obese eat more because of a faulty
'switch' and exercise less because of a low energy state. If you
can learn how to control the specific 'switch' located in the
powerhouse of each of your cells – the mitochondria – you hold
the key to fighting obesity."
There are five basic truths that Dr. Johnson explains in detail
in his most recently book, The Fat Switch, that overturn
current concepts:
- Large portions of food and too little exercise are NOT
solely responsible for why you are gaining weight
- Metabolic Syndrome is actually a healthy adaptive condition
that animals undergo to store fat to help them survive
periods of famine. The problems is most all of us are always
feasting and never undergo fasting. Our bodies have not adapted
to this yet and as a result, this beneficial switch actually
causes damage to contemporary man
- Uric acid is increased by specific foods and causally
contributes to obesity and insulin resistance
- Fructose-containing sugars cause obesity not by calories
but by turning on the fat switch
- Effective treatment of obesity requires turning off your fat
switch and improving the function of your cells' mitochondria
I highly recommend picking up a copy of this book, which is a
useful tool for those struggling with their weight. Dietary sugar,
and fructose in particular, is a significant "tripper of your fat
switch," so understanding how sugars of all kinds affect your weight
and health is imperative.
Study: Midnight Snacks Can Mess You up on a Molecular Level
I have long advocated that avoiding all food for at least three
hours before you go to bed is an exceedingly helpful strategy for
those seeking to maintain a healthy weight. This will lower your
blood sugar during sleep and help minimize damage from too much
sugar floating around. Additionally, It will jump start the glycogen
depletion process so you can shift to fat burning mode.
A recent study9
is a powerful confirmation of this recommendation as it has found
that the mere act of altering your typical eating habits — such as
getting up in the middle of the night for a snack — causes a certain
protein to desynchronize your internal food clock, which can throw
you off kilter and set a vicious cycle in motion. As reported by
The Atlantic:10
"Along with the usual slew of eating-related disorders,
like obesity and diabetes, the researchers believe that this
molecular understanding for why changing our eating times messes
up our food clock might allow them to come up with novel
treatments for conditions such as 'midnight hunger,' and to make
better recommendations for people suffering the consequences of
jet lag or working the night shift."
Your internal body clock, also known as your circadian rhythm,
helps regulate the energy levels in your cells, and the proteins
involved with your metabolism are intrinsically linked to your
circadian rhythms. There's strong evidence that proper sleep and
diet can help maintain or rebuild the balance between your circadian
clock and your metabolism, and that lack of rest or disruption of
normal sleep patterns can increase hunger, leading to
obesity-related illnesses and accelerated aging.
In terms of its effect on your metabolism and weight, lack of
sleep has been shown to affect levels of leptin and ghrelin—two of
the hormones linked with appetite and eating behavior. When you are
sleep deprived, your body decreases production of leptin, the
hormone that tells your brain there is no need for more food, while
increasing levels of ghrelin, a hormone that triggers hunger. (These
are the same hormones detrimentally affected by a high-fructose
diet, as discussed above.)
To keep your circadian clock functioning properly, make sure
you're getting the necessary amount of high quality sleep, during
those hours when your body expects to be sleeping. The right amount
for you is based on
your individual sleep requirements and not on a
one-size-fits-all prescribed number of hours. For helpful guidance
on how to improve your sleep, please review my
33 Secrets to a Good Night's Sleep.
The Case for Intermittent Fasting to Optimize Your Circadian Clock
In addition to that, this study offers an indication of how
important it is to also maintain a regular eating schedule.
Personally, I believe there is good reason to consider an
intermittent fasting schedule. There is an emerging consensus
that narrowing the window of time that you consume food may have
enormous health benefits and also help you reduce your percentage of
body fat.
Your suprachiasmatic nucleus (SCN), located in your hypothalamus,
controls your circadian rhythms. It regulates how your autonomic
nervous system operates along with your hormones, your wake and
sleep pattern, your feeding behavior, and your capacity to digest
food, assimilate nutrients, and eliminate toxins.
If you routinely disregard your innate clock – working during
sleeping hours, or feeding at the wrong time – you will sooner or
later suffer the consequences with symptoms that may include
disrupted sleep, agitation, digestive disorders, constipation,
chronic fatigue, chronic cravings for sweets and carbs, fat gain,
and lower resistance to stress. Chronic disruptions in circadian
rhythms have also been linked with increased risk for chronic
inflammatory disease and cancer.
As explained by fitness expert
Ori Hofmekler, the ideal time to eat is in the evening. Having a
large meal during the day will inhibit your sympathetic nervous
system (SNS) and instead turn on the parasympathetic nervous system
(PSNS), which will make you sleepy and fatigued rather than alert
and active. And, instead of spending energy and burning fat during
the day, you'll store energy and gain fat.
The one meal per day plan can accommodate your innate clock and
maximize the beneficial effects you get from intermittent fasting on
a daily basis. This form of
intermittent fasting involves timing your once-daily meal to
within a narrow window of time in the evening. However, you don't
have to be that strict if you can't function without a mid-day meal.
I've revised my own eating schedule to eliminate breakfast and
restrict the time I eat food to a period of about six to seven hours
each day, which is typically from noon to 6 or 7 pm. This still
gives me a net fasting time of 17-18 hours a day. To learn more,
please see my previous article,
The Power of Intermittent Fasting.
© Copyright 1997-2013 Dr. Joseph Mercola. All Rights Reserved.
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