I have recently introduced you to the book Body by Science by Doug McDuff, MD and
John Little. This book offers a clear explanation of the actual science of
exercise, how activity relates to hormones, and how this determines what
happens in your body. In short, it answers the question I am frequently asked.
“Why am I gaining weight when I am working out every day?”
In the introductory article I summarized his key points. In
this article I will address one of those key points. The effectiveness of
exercise is all about hormones, fat metabolism and blood glucose levels. Hormones
signal the body to burn fat and to store fat. High intensity training works the
major muscle groups to exhaustion, uses up glucose, and encourages the body to
burn fat and build muscle.
First, here’s a little background on fat. Fat is not the
evil it is made out to be – either the fat we eat or the fat on our body. Fat
(and the ability to store fat) is why humans have survived the many droughts,
famines, and lean times in our history. Fat is how we store energy for future
use. As I like to say, there were no refrigerators in the Garden of Eden.
Having food available 24/7 is somewhat new in human history. Our ancestors ate
when food was available and stored the excess as fat, allowing us to survive.
There’s also a popular myth that our hunter-gatherer
ancestors were way more active than we are today, but there is little evidence
of that. In fact it is not very likely. Since they didn’t have food all the
time they would need to conserve their energy to find food and survive! Modern
obesity is not from lack of exercise, but from too much food (and poor quality
food at that – although that’s another series of articles!). For
most of human history fat storage was essential to survive. Unfortunately today
it now leads to obesity and chronic disease.
As mentioned earlier the key to exercise is how it impacts
hormones. To understand this we need to look at how our body accesses and
stores energy. The following explanation is simplified for the purposes of this
discussion. It starts with our body breaking down food into useable components.
One of these is glucose which goes into the blood stream. From there, glucose
enters cells and is used to produce energy. Excess glucose, beyond what the
cells are calling for, needs to be stored. The first storage sites are the
muscles and liver where it is stored as glycogen. After that it is stored in
fat cells.
The main benefit of high intensity training is the depletion
of glycogen stores from the muscles. When glycogen is moving out of storage the
hormone called hormone sensitive lipase is released. This allows body fat to be
mobilized and burned for energy. Eventually the glycogen levels will be
restored in the muscles coming from this mobilized fat.
In traditional cardio the glycogen is not released to the
same extent. The muscles retain some glycogen, glucose remains in the blood
stream and insulin is required to move the glucose out of the blood stream.
Since the body does not sense a need to build glycogen stores the glucose is
stored as fat. This may also have the effect of keeping insulin elevated which
ultimately can lead to insulin resistance. Also when insulin is high, hormone
sensitive lipase is inhibited.
Another hormone that gets into the act is called leptin.
Leptin is our satiety hormone – it tells us we are full. The more fat we have,
the more leptin is produced so that our appetitive will decrease and our body
fat level will stabilize. A modern day problem has become leptin resistance.
Similar to insulin resistance our body is not able to respond to all the excess
leptin being produced so we are not properly getting the signal that we are
full and should stop eating.
The bottom line is that HIT will lower insulin, leptin, and
cortisol levels while increasing growth hormone while traditional cardio or
“aerobics” will have the opposite hormonal effect.
A few other points of interest:
One of the big truth stretchers of the fitness industry is
the measuring of “calories burned” on machines. We have what is called our
basal metabolic rate. Just by living we burn calories. The BMR is how many
calories you burn just by being alive at that moment. The calories burned being
recorded by the machines are inclusive of those calories. The “calories burned”
is highly misleading as if you stood on the machine and did nothing you’d still
be burning calories!
Another basic truth is that no exercise per se burns a lot
of body fat. As explained earlier, we survived by being very efficient with our
fat. It is what kept us alive. So, if we were burning lots of fat by hunting
and gathering or any other activity, it would jeopardize our ultimate survival.
In conclusion, our body developed ways to survive food
scarcity so we could endure as a species. It was not designed for food
abundance. Our modern diet which is high in carbohydrates keeps our blood
glucose levels elevated, which keeps our insulin levels high, which keeps our
glycogen stores high, so we are not able to burn fat.
And one last key factor is hydration. Most people do not
drink enough water. Being properly hydrated improves our liver function which
will support fat metabolism and improves cell structure so hormone receptors
work properly. And, drought precedes famine. If we are not properly hydrated we
are sending an evolutionary signal to our body to hold on to fat as it prepares
for the upcoming famine.
Bernard Rosen, PhD is a Nutrition Consultant and
Educator. He works with individuals, groups, and at corporations to create
individualized nutrition and wellness programs. His office is in Mequon, WI. To
learn more or to schedule an appointment, e-mail at bernie@brwellness.com, call
(262) 389-9907 or go to www.brwellness.com.
Posts
No comments:
Post a Comment