How Exercise Influences Hunger and Weight Loss
October 05 2012
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Recent research shows that 45 minutes of moderate-to-vigorous
exercise in the morning may reduce food cravings, both immediately
afterward and throughout the day
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Exercising first thing in the morning, especially if done on an
empty stomach, has been shown to have a number of health benefits,
including preventing weight gain and insulin resistance
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Your choice of breakfast food may play a significant role in
decreasing or heightening sensations of hunger afterward.
Carbohydrate-rich breakfast foods can significantly increase hunger
especially if you are lean, with healthy insulin sensitivity
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Previous research has revealed that exercise may also help control
your body weight by altering hormones released by your gut after a
meal
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When exercising in a fasted state, its critical to eat a recovery
meal within 30 minutes post-workout. This meal should NOT be skipped
in the name of fasting. Fast-assimilating protein, such as whey, is
ideal for brain and muscle recovery
By Dr. Mercola
A common assumption about exercise is that it will
motivate you to eat more. But recent research turns this
assumption on its head by showing that 45 minutes of
moderate-to-vigorous exercise in the morning may actually
reduce your food cravings.1
The study included 18 women of normal-weight, and 17 who
were clinically obese. Their neural activity in response to
images of food was measured on a morning following exercise,
and on a morning when they did not exercise.
Images of flowers were used as a control. Perhaps
surprisingly, they discovered that the women's attentional
responses to images of food decreased after a brisk walk on
the treadmill.
According to co-author James LeCheminant:2,3
"This study provides evidence that exercise not
only affects energy output, but it also may affect how
people respond to food cues... We wanted to see if
obesity influenced food motivation, but it didn't.
However, it was clear that the exercise bout was playing
a role in their neural responses to the pictures of
food."
In both groups of women, morning exercise also resulted
in an increase in total physical activity that day, and,
perhaps more importantly, they did not compensate for the
energy expenditure by eating more later in the day.
According to the authors, further research is needed to
determine whether or not the diminished motivation for food
persists long-term if you exercise regularly. I would
counter that by pointing out that the evidence supporting
exercise for normalizing your weight and approach to food is
so overwhelming, you really don't need to wait for such
results... Exercising first thing in the morning, especially
if done on an empty stomach, has been shown to be
particularly beneficial. Your choice of
breakfast food may also play a significant role in
decreasing or heightening sensations of hunger afterward.
Why Eating Breakfast Might Increase Hunger
The interesting aspect about eating first thing in the
morning is that it coincides with your circadian cortisol
peak, that is, the time of day when your cortisol (stress
hormone) levels rise and reach their peak. The circadian
cortisol peak impacts your insulin secretion in such a way
that when you eat during this time, it leads to a large and
rapid insulin release and a corresponding rapid drop in
blood sugar levels, more so than when you eat at other times
of the day.
If you're healthy, your blood sugar levels won't drop to
a dangerously low level (such as what can occur with
hypoglycemia) but they can drop low enough to make you feel
hungry. This is more commonly experienced in people who are
not insulin resistant (such as those who are
overweight or have type 2 diabetes), but rather are lean and
"insulin sensitive." Because the circadian cortisol peak
adds another insulin-boosting effect on top of an already
insulin-sensitive individual, the low blood sugar and
subsequent hunger may therefore be more pronounced.
It's also important to realize that eating a full meal,
particularly carbohydrates, will inhibit the
sympathetic nervous system (SNS) and reduce the fat
burning effect of your exercise. Instead, eating lots of
carbs activates your parasympathetic nervous system (PSNS),
which promotes energy storage the complete opposite of
what you're aiming for.
Although conventional wisdom states breakfast is the most
important meal of the day, skipping breakfast may
actually help you control your appetite throughout the day.
Skipping breakfast is also an easy way to implement
intermittent fasting, which has a number of well-documented
health benefits, including weight loss and improved weight
management as you become increasingly
fat-adapted.
Keep in mind that it takes about six to eight hours for
your body to metabolize your glycogen stores and it's only
after that that you actually start to shift to
primarily burning fat as fuel. If you keep replenishing your
glycogen by eating every eight hours, you make it far more
difficult for your body to actually shift to fat burning
mode, so when using intermittent fasting, make sure your
fasting period is long enough (12-18 hours). You will need
to start gradually though and take a few weeks or more to
get to 12 hours and eventually longer.
I have revised my personal eating schedule to eliminate
breakfast and restrict the time I eat to a period of about
six to seven hours, typically from noon to 6 or 7 pm. Our
ancestors rarely had access to food 24/7 like we do today,
and it makes sense that our genes are optimized for
intermittent fasting. On the days that I exercise in the
morning, I will have two scoops of Pure Power Protein about
30 minutes after the workout to provide nutrients,
especially leucine, for muscle growth and repair.
A growing body of intriguing research indicates that
intermittent fasting may be a key weight loss tool
especially when combined with
exercise in a fasted state and this has been true in
my personal experience as well. Since adopting this approach
for the past few months I have lost two inches from my waist
size and gained three pounds, which means I have lost body
fat and gained muscle mass.
Health Benefits of Exercising on an Empty Stomach
Research has shown that exercising on an empty stomach is
useful for preventing both weight gain and insulin
resistance, which is a hallmark of countless chronic
diseases. One of the explanations for this is that your
body's fat burning processes are controlled by your
sympathetic nervous system (SNS), and your SNS is activated
by exercise and lack of food. The combination of fasting and
exercising maximizes the impact of cellular factors and
catalysts (cyclic AMP and AMP Kinases), which force the
breakdown of fat and glycogen for energy.
This is why training on an empty stomach will effectively
force your body to burn fat.
Intermittent fasting calls for you to exercise in late
morning or early afternoon, and fasting (or eating only
light raw foods, vegetable juice and/or whey protein or
eggs) until 30 minutes after your workout. If you
have trouble exercising on an empty stomach, you can include
20 grams of a fast-assimilating protein like a
high-quality whey protein concentrate 30 minutes before your
workout.
Exercise and fasting result in acute oxidative stress,
which keeps your muscles' mitochondria, neuro-motors and
fibers intact. You may have heard of oxidative stress before
in a negative light, and when it is chronic it can
lead to disease. But acute oxidative stress, such
as that which occurs due to short intense exercise or
periodic fasting, actually benefits your muscle. In
fact, according to fitness expert
Ori Hofmekler:
"[Acute oxidative stress] is essential for
keeping your muscle machinery tuned. Technically, acute
oxidative stress makes your muscle increasingly
resilient to oxidative stress; it stimulates glutathione
and SOD production in your mitochondria along with
increased muscular capacity to utilize energy, generate
force and resist fatigue.
Hence, exercise and fasting help counteract all
the main determinants of muscle aging. But there is
something else about exercise and fasting. When
combined, they trigger a mechanism that recycles and
rejuvenates your brain and muscle tissues."
The mechanism he refers to is triggering genes and growth
factors, including brain-derived neurotropic factor (BDNF)
and muscle regulatory factors (MRFs), which signal brain
stem cells and muscle satellite cells to convert into new
neurons and new muscle cells, respectively. This means that
exercise while fasting may actually help to keep your brain,
neuro-motors and muscle fibers biologically young. The
combined effect of both intermittent fasting and short
intense exercise may go way beyond helping you to burn more
fat and lose weight; it may help you to:
Turn back the biological clock in your muscle and
brain |
Boost growth hormone
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Improve body composition
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Boost cognitive function
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Boost testosterone
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Prevent depression
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Exercise May Also Influence Satiety and Weight by its Effect
on Gut Hormones
While we're on the topic of food and exercise, an
interesting study presented at the 2011 meeting of the
Society for the Study of Ingestive Behavior (SSIB) revealed
that exercise may help control your body weight by altering
the hormones released by your gut after a meal.4
In rats that exercised, increased levels of an inhibitory
feeding hormone, amylin, were released when a meal was
eaten, and a more rapid rebound of ghrelin occurred after
the meal. Further, exercised rats treated with a gut hormone
called CCK, which limits meal size, decreased their food
intake more so than sedentary rats.
According to one of the study's authors:5
"Our new results indicate that the beneficial
effects of exercise to control body weight might occur
by altering the way in which meals release gut hormones
that regulate food intake, and also by changing the
sensitivity of individuals to these gut hormone
signals."
Exercise is already known to increase sensitivity to
leptin, the "satiety hormone" involved in appetite
regulation, providing even more reason to make physical
activity a regular part of your life, especially if you're
struggling with overeating.
Tips for Fasting and Exercising Safely
While exercise and fasting help counteract muscle aging
and boost fat-burning (compared to working out after
eating), fasting incorrectly can cause more harm than good.
To start, you need to make sure that you're not fasting to
an unhealthy extreme. In other words, fasting does not mean
that you starve yourself for days. Instead, intermittent
fasting involves restricting your food intake during the day
to a smaller time window (typically six to eight hours).
When you add exercise to the mix, you complete your
workout while fasting, but this must be followed by
a recovery meal within 30 minutes of your workout. This is
very important and should not be skipped. Whey protein is
ideal, as it is fast-assimilating and will provide you with
the nutrients your muscles need for recovery. (Make sure to
avoid any and all sources of fructose as this will
sabotage the health benefits of your exercise! This
means avoiding virtually all sports drinks and juices.)
Then, you eat one single, main meal at night.
Skipping the recovery meal after exercise is very ill
advised, as it can lead to brain and muscle damage. So
please, do not take your fasting to the extreme by skipping
this meal.
Ori explains:
"When you implement intermittent fasting you put
your body into a strong catabolic state. Your body is
literally eating up and destroying damaged and injured
brain and muscle cells. You rapidly accelerate this
process when you exercise in this state. It's this very
powerful synergy that will allow you to effectively
rejuvenate your muscle and brain. This is the radical
new approach that very few know about and even fewer
have implemented.
The MAJOR danger though is that you will need to
rescue your muscle tissue out of this catabolic state
and supply it with the proper nutrients to stimulate
repair and rejuvenation. If you fail to supply these
nutrients at the proper time you will hurt yourself.
Your post exercise recovery meal is critically
important. It's needed to stop the catabolic process in
your muscle and shift the recycling process towards
repair and growth. If you fail to feed your muscle at
the right time after exercise, you won't just miss this
window of opportunity to restore and build your muscle,
you'll actually let the catabolic process go too far and
potentially waste and damage your muscle."
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