By Dr. Mercola
What you eat can either add to or take away
from your
exercise benefits, and if you're devoting the time to
working out, you want to know how to harness your meals to
support your efforts, not detract from them. Choosing the proper
foods is important, but so is the timing of when you
eat them.
Men and women are different in this respect, according to an
experiment featured on the BBC's "Trust Me I'm A Doctor"
program. Women who exercise, for instance, may be able to burn
22 percent more fat just by tweaking the timing of their meals.
Women May Burn More Fat by Eating Before Exercise; Men by Eating
After
In an experiment of 30 men and women by Adam Collins, Ph.D.,
nutrition consultant and senior lecturer in nutrition at the
University of Surrey, participants took part in three fitness
classes a week (high-intensity
training, Zumba and spin class).
They consumed a drink — either a caloric carbohydrate
beverage or a zero-calorie placebo beverage — before and after
class.
Women burned more fat overall than men, but the women who
consumed the carbohydrate drink prior to exercise burned up to
22 percent more fat. Among men, however, those who consumed the
carbohydrate drink after exercise burned up to 8 percent more
fat.1
The discrepancy likely has to do with the body’s preferred
source of fuel. Men tend to have more muscle, where
carbohydrates are stored, making this their preferred fuel.
Women, on the other hand, may burn fat more readily in order to
conserve carbohydrates. Collins told the Daily Maill:2
"Women have more fat around hips, bums and tums,
better release of fatty acids into the blood, hormonal
differences which mean they can be better and more frugal at
conserving glucose [sugar from carbohydrates] and burning
fat.
'This is probably an evolutionary advantage to do
with pregnancy. If women are better at managing their fuels
they have glucose to spare for the fetus.'"
Women May Want to Avoid Eating for 90 Minutes After Exercise
When men exercise in a fasted state, they limit their source
of carbohydrates as fuel, which means the muscles may then burn
more fat. Women, however, tended to burn the most fat in the
three hours after exercise.
Because of this, Collins recommended women avoid eating for
at least 90 minutes after exercise. If you women choose to eat
in this timeframe, it provides the body with carbohydrates to
burn, which means your body may not shift into beneficial
fat-burning mode.
Men, however, can eat after exercise and still maximize their
fat burning.3
It should be noted that this study only looked into the effects
of consuming carbohydrates — not proteins and/or fats. It would
be interesting to see if the results differed depending on the
types of foods consumed.
If You're Fat Adapted, You Need Very Little Carb Replacement,
Even During Exercise
If you've been following a low-carb, Paleo-style diet, or a
high-fat, moderate-protein, low-carb diet like the one described
in my
nutrition plan, your body is probably fat adapted.
Our ancestors were adapted to using fat as their primary
fuel, but over 99 percent of Americans are now adapted to using
sugar or glucose as their No. 1 fuel source instead.
One way to tell if you're fat adapted or not is to take note
of how you feel when you skip a meal. If you can skip meals
without getting ravenous and cranky (or craving carbs), you're
likely fat-adapted.
Being able to rely more on fat for energy during exertion
spares your glycogen for when you really need it. This can
improve athletic performance and helps burn more body fat.
As explained by former Ironman triathlete Mark Sisson, if you
can handle exercising without having to eat carbs first, you're
probably
fat-adapted.
If you can work out effectively in a fasted state, you're
definitely fat-adapted. Replacing non-vegetable carbs with
healthy fats, and fasting intermittently, are among the most
effective ways to encourage your body to change from burning
carbs to burning fat.
So for those of you already following a high-fat, low-carb
diet, you're likely quite efficient at burning fat for fuel and
will require very little carb replacement even during intense
exercise.
If you're a competitive athlete, there is some evidence that
switching to a
higher-carb diet just before a race (after you've been on a
low-carb diet) can help to "top off your tanks" to boost your
performance, but this is highly individual.
For many, this strategy may backfire, as the sudden carb
consumption may lead to headaches, nausea, bloating and other
symptoms as well.
What Are the Benefits of Exercising in a Fasted State?
The featured study suggests men do best exercising in a
fasted state, which for many simply means exercising first thing
in the morning, prior to breakfast. For women, you may want to
listen to your body and monitor your fitness goals to see if
this is a beneficial strategy for you as well.
When you exercise while fasting, it essentially forces your
body to shed fat, as 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.
On the other hand, eating a full meal, particularly
carbohydrates, before your workout will inhibit your sympathetic
nervous system and reduce the fat-burning effect of your
exercise.
Eating lots of carbs activates your parasympathetic nervous
system, (which promotes energy storage — the complete opposite
of what you're aiming for).
One study found, for example, that fasting before aerobic
training leads to reductions in both body weight and body fat,
while eating before a workout decreases only body weight (this
study included only men).4
Beyond Fat Burning: Reasons to Exercise While Fasting
Exercise and fasting together also yields acute oxidative
stress, which actually benefits your muscle trigger genes and
growth factors. This includes 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 |
Improve body composition |
| Boost cognitive function |
Boost testosterone |
Prevent depression |
This strategy would probably not be appropriate for long
endurance exercise, but for the vast majority of casual
exercisers, it can be quite beneficial. One of the easiest ways
to do this for most people is simply to exercise before eating
breakfast, as you've been fasting since your dinner the night
before.
One exception to fasting before exercise is if you are doing
strength training. When you are fasting for 14 to 18 hours
you typically deplete most of your glycogen stores, which makes
it difficult to lift your maximum weight to failure.
Hence, if you are doing heavy lifting to failure, you may
want to avoid training while fasting. In these cases it is
likely helpful to consume some healthy slow-releasing starchy
carbs the night before working out so your glycogen stores won't
be depleted in the morning.
Then, have whey protein as a pre-exercise meal to grant
sufficient supply of branched-chain amino acids for optimum
muscle fueling during your workout.
What Are the Best Foods to Support Your Workouts?
As noted by sports nutritionist Susan M. Kleiner, R.D., Ph.D,
"When it comes to sculpting your body and enhancing your
performance, without a diet to support your training you are
wasting your time in the gym."5
The best food for your workouts depends on your personal and
fitness goals, health status and possibly your sex as well.
However, in general fitness expert Ori Hofmekler recommends
flooding your body with
stress-activated food nutrients (SAF nutrients) prior to
exercise, as these nutrients mimic the effects of intermittent
fasting and exercise. He explains:
"Once ingested, SAF nutrients demonstrated the
capacity to increase animal and human survivability. Some of
these nutrients have shown to mimic the anti-obesity,
anti-diabetic, and anti-aging effects of exercise and
fasting on the body. The point is, food rich in those
exercise-mimicking nutrients is ideal for pre-workout. Not
only that it can prevent setbacks with the fat burning and
healing impact of exercise, it may actually enhance that
impact.
… Note that some of the most potent SAF nutrients are
no longer part of our diet. These hard-to-find nutrients
occur in barks, roots, pits, and peels, which we don't
normally eat. However, some foods within our reach contain
high levels of exercise-mimicking SAF nutrients such as
phenols, caffeine, theobromine, catechins, and immune
proteins and thus can potentially yield powerful synergy
with physical training."
Try Eating This Before Your Workout
Exercising while fasting may work for some people, but if you
find it difficult to exercise on an empty stomach then SAF
nutrients may be optimal for you. So where are these nutrients
found?
- Whey protein from grass-fed cows
- Organic black coffee
- Unsweetened cocoa
- Green tea
Take, for instance, a study published in the journal Medicine
and Science in Sports & Exercise. It demonstrated that
consuming whey protein (20 grams protein/serving) 30 minutes
before resistance training boosts the body's metabolism for as
much as 24 hours after your workout in both men and women.6
It appears as though the amino acids found in high-quality
whey protein activate certain cellular mechanisms (mTORC-1),
which in turn promote muscle protein synthesis, boost thyroid,
and also protect against declining
testosterone levels after exercise.
I believe the best approach is to use some common sense and
listen to your body. If you feel weak or nauseous while
exercising on an empty stomach, you may want to eat a small
meal, such as a high-quality whey protein shake, as mentioned,
before your workout.
Should You Eat Breakfast on Non-Exercise Days?
Should your morning routine include a healthy breakfast?
Conventional nutritional dogma states that breakfast is the most
important meal of the day, but if you're not a fan there's no
harm in skipping it, as
skipping breakfast extends the natural time of your
overnight fasting period.
This type of
intermittent fasting has numerous benefits for your health.
That being said, if you enjoy breakfast and feel better when you
eat it, it can certainly be part of a healthy morning routine.
Examples of breakfast foods that include healthy protein are
organic pastured eggs (soft boiled, poached or raw), a whey
protein smoothie, or leftovers from a healthy dinner.
You don't want to
consume too much protein either, but when your breakfast
contains a moderate amount, research shows it alters signals in
your brain that control food motivation and reward-driven
behavior, making it a potential strategy to reduce reward-driven
eating behavior and potentially help with weight loss.7
The key to remember is that your body probably only needs
two meals a day, and eating this way allows you to restrict
your eating to a window of six to eight consecutive hours each
day, and avoid food for at least three hours before bedtime.
As long as you restrict your eating to a six to eight-hour
window, and avoid eating for at least three hours before bed,
you can choose between having breakfast and lunch, or lunch and
dinner, but avoid having both breakfast and dinner.
Which two meals you prefer are up to you; let your body, and
your lifestyle, including your workout schedule, be your guide.