By John Cardillo
When understanding how your body uses macronutrients for fuel its best to
take a look back instead of taking a look forward. Meaning, let's say you
could take a ride on a time machine back to the age of our hunter-gatherer
brethren. Once you stepped off the time machine and took a look at the
specimen that was once your relative, you would be shocked to see how
impressively built they were. Your ancient relative stood tall, was lean
and muscular, had broad shoulders, and could run down animals. Most likely,
your ancient relative was way more impressive looking than you are today in
the 21st century, minus the long hair and loin cloth. But how could this
be? This hunter-gatherer didn't have access to a gym, grocery store,
personal trainer, or a fancy workout plan. The physique of your
hunter-gatherer brethren was the result of the lifestyle of the time. Days
that were filled with lots of walking and moving across great distances of
terrain, gathering whatever edible plants and fruits one could find, setting
up shelter, and hunting dangerous game. Now before understanding how this
hunter gather lifestyle plays into how your body uses macronutrients for
fuel, you must understand that your body and physiology still thinks that it
is the age of hunter-gatherers. We simply have not had enough genetic
mutations over the last 10,000-15,000 years; our bodies still believe it is
15,000 BC.
The preferred energy source that your body wants to use is fat. Fat yields
9kcal of energy per gram, opposed to 4kcal of energy for carbohydrates and
protein. When your hunter-gatherer brethren were trekking across the tundra
for dozens of miles per day, they were surely burning fat for energy.
However, when it came time to chase down that animal that would become
dinner, carbohydrates in the form of muscle glycogen would be used. They
key differences here lie in intensity. For lower intensity activity, such
as walking across vast distances of land, the preferred fuel source is fat,
because it will give a longer steady level of energy. For higher intensity
activities, such as running down and killing an animal, carbohydrates become
the main fuel source. The premier source for fitness activity of a high intensity nature is carbohydrates. However, the carbohydrate
fuel source is limited and will not last nearly as long as fat. A 170lb
male has 3,500 grams of carbohydrate stored versus 70,000 grams of fat.
This takes us back to trekking across the tundra. If we were burning
carbohydrate we would run through our resources relatively quick and would
have no fuel source for any high intensity activity, such fighting or
hunting. A hunter-gatherer's day revolved around lots of low intensity
activity with bouts of high intensity activity. For fuel sources, we rely
on fat to fuel our low intensity activities and carbohydrates for high
intensity activities.
Unfortunately, today our lifestyles and diets do not resemble anything close
to those of our hunter-gather brethren. Today we are cooped up inside all
day sitting in front of a computer screen and are wreaking havoc on our
physiology. Despite sitting down and not receiving anything close to normal
daily activity, our diets consist of great amounts of carbohydrates that are
nutrition-less and do not fuel any high intensity activity. This paradox is
what has led to a great prevalence of obesity, with 70% of the population
being classified as overweight or obese. What people need to do is take a
page out of the book of our hunter-gather brethren and introduce lots of low
intensity daily activity, in the form of walking, gardening, standing, using
a standing work-desk, cleaning, riding a bike. After incorporating
considerable increases in daily activity, we need to mix in bouts of high
intensity, such as weight training, sprinting, jumping, boxing, or wrestling.
The bouts of high intensity exercise will justify the carbohydrates that you
are in taking.
So what does this mean for you in regards to your training? It means that
you need to be more cognizant of how your physiology relies on primal human
traits that are the result of hundreds of thousands of years of evolution.
If you want to get your health back on track, shed excess body fat, look
better, and feel better, then you need take steps to change your lifestyle,
not just try to exercise a little differently.
Once you have gained a basic understanding of your physiology and understand
the lifestyle changes that you need to make, you are ready to become a fat
burning beast. First, you must keep your blood glucose levels down,
otherwise your body will prefer this fuel source because of its easy access,
and will store excess glucose as adipose fat (the unsightly fat under your
skin that you don't want!). When keeping your glycemic load down by eating
less sugary foods and fewer carbohydrates, your body will fuel itself with
fats. Fat uses different metabolic pathways than carbohydrates and are
broken down slowly in the gut by enzymes known as lipases. Dietary fat is
broken down into free fatty acids for energy. These fats provide a powerful
fuel source that can power your activity for long periods of time, depending
upon the intensities of the activities you are doing.
But what about adipose fat? The fat that is under your skin and makes you
look unsightly. Your body will use adipose fat for energy as well in a
similar manor. Adipose fat is stored as readily available energy in the form
of triglycerides. When you are doing activity and have burned through
dietary fat and carbohydrates, your body will now use a process called
lipolysis to use adipose fat for energy. Again, this is not the preferred
fuel source during high intensity activity, but it is a fuel source that can
provide seemingly endless supplies of energy. The same energy that was
needed 15,000 years ago for our hunter-gatherer brethren that may not have
been able to eat for days at a time before they landed a big hunt. Once you
have reached this state of energy metabolism, you are becoming a fat burning
beast. This however, does not mean that you should constantly starve
yourself to train, carbohydrates and protein play vital roles in health.
One needs to understand how to properly use carbohydrates and protein to
fuel and recover so they do not go into a circle of weight-loss and
weight-gain.
So as a science, how exactly do you get into your fat burning zone? It
still depends on intensity, and the substrate source that is readily
available. To understand intensities, there are two simple measuring points
you should know, VO2max and heart rate. VO2max is simply the maximum amount
of oxygen that you can consume to keep up with metabolic demands, the harder
you work, the more oxygen you are going to need. Gaging hear rate is also
fairly simple, the harder you work the faster your heart is going to pump in
order to keep up with demands, and your maximum heart rate is defined as 220 less your age.
In a fasted stated, fat is going to be the predominate fuel source. During
rest to very low intensity activity (25% VO2max) your body uses primarily
(85%) FFAs (free fatty acids) that are found in the blood stream. As
intensities increase (65%VO2max), your body will use about half FFAs in the
blood stream and half intramuscular triglycerides. This 65% Vo2 max sweet spot is the zone where you will be specifically burning fat. You are now consuming oxygen at fairly high rate, meaning you are breathing heavy but not gasping for air. What you should know is that your body wants to hold on
to stored muscle glycogen for the absolute most important times. Times
where you need to run away from that sabertooth tiger or sprint down an elk
to go in for the kill. That is why your body is not using glycogen all day
long to fuel you for average tasks. With increasing intensities (85% VO2max
or higher), your body is now going to use about 1/3 fat for energy and 2/3
stored carbohydrate for energy. The fat that is going to be used during
these high intensities is intramuscular triglycerides, and the carbohydrates
are going to be stored muscle glycogen. Typically, this is where you see a
decrease in performance with prolonged activity (>30 mins), because your
carbohydrate stores are limited and fat is not a great fuel source for high
intensity activity. The exact term is called beta oxidation (slow
glycolysis), as part of the aerobic energy system. The process takes place
in the cell mitochondria after fat has been broken down into acetyl CoA.
Here, oxidized fat (acetyl CoA) goes through the krebs cycle and then the
electron transport chain to yield ATP to fuel your body.
What's an easy way to know you are in the fat burning zone? Well there is an
equation for that; it's called the 180 formula. One simply subtracts their
age from 180. This is not to be confused with the max heart rate formula,
which is 220 minus your age. Now you subtract your age from 180 giving you
a much lower number. This is your aerobic fat burning zone. There are a
few modifications that must be taken into consideration. If you have any
health problems such as injury, obesity, allergies, asthma, two or more
bouts of the flu per year, or have been inconsistent with training, you add
an additional 5 to the number that you subtract. If you have been training
consistently for four days a week for over two years you will only subtract
5 from your age. An example being a man who is 32 years old who has trained
consistently for over two years; (180-27=153). For this person, their fat
burning heart rate zone is 153. An easy way to know you are in this zone is
if you can have a conversation with someone while you are doing cardio and
you do not feel out of breath. If you want to use V02 max as a gauge, there
is a simple way to do so, you can run a mile and a half as hard as you can,
then measure time to your sex/age/bodyweight. This
means that your pushing enough oxygen through your body that you are just
burning fat. At first, this heart rate might seem way too low to effectively
burn fat, however, you have not become an effective fat burner at this
stage. You may only be able to run 12-minute miles during this period. Over
time, your body will become efficient at training in this zone and your time
could drop to as low as 7-minute miles all at the same heart rate. When
this is accomplished, you have become an effective fat burner and your body’s metabolic engine will have a seemingly endless fuel tank.