Did you know that there roughly 30 calories in 10 baby
carrots? 120 calories in a 3 oz portion of grilled chicken breast with no
additional oils or flavorings -- the same amount that is present in a regular
can of pop?
What is the nutritional difference between these items? How
many calories do I need per day? If I’m supposed to have 1200 calories, why
can’t I just have 10 Pepsi’s?
We need varying amounts of macronutrients because we have
different hormonal balances and physical activity patterns. Gender, type,
duration, and intensity of workout can play a very large role in your diet.
My goal for this discussion is to present energy to you in
terms of biochemical processes instead of calories. I’m going to warn you that
there may be words or concepts that you’ve never heard of our can’t pronounce. Don’t
let this discourage you! You are smart and capable. Take the time to research
things you don’t understand or, better yet, leave your comments and
questions.
WHAT IS A CALORIE?
A calorie is simply a measure of heat. The word stem calor-
comes from Latin and means “heat”. The calorie that we know is actually a
kilocalorie. A true “calorie” is the amount of energy needed to raise 1 gram of
water by 1 degree Celsius. Thus, a kilocalorie is the amount of energy needed
to raise 1 kilogram of water by 1 degree Celsius.
Heat is the byproduct of a release of energy. The food we
take in, along with the energy that our body is able to synthesize and reuse,
goes through a series of catabolic reactions (breaking these molecules down) in
order to optimize potential energy and use this energy to carry out
physiological processes that keep us alive. Heat (and carbon dioxide) are then
released as byproducts of macronutrient metabolism. This is what it means to
take in and then burn off calories through diet and exercise.
WHAT IS ATP?
ATP stands for “adenosine triphosphate”. The structure of
ATP has an ordered carbon compound as a backbone (adenosine is a nucleoside),
which is essential because it is able to be hold up in the cytosol of the cell
– an aqueous solution. The triphosphate part of the molecule is the key player
for creating energy but cannot stand alone in an aqueous solution because its
bonds cannot hold up against those of water. Tri = three, so ATP has three
phosphate groups. These phosphate groups are connected by oxygens to eachother
and to the adenosine part. The oxygens carry a negative charge and want to be
near a positive charge, so they are constantly repelling one another. That
means there is a LOT of potential energy
stored in these bonds.
Removing just one phosphate group from the end makes ATP
very happy. It changes ATP to ADP, adenosine diphosphate (two phosphate
groups). The reaction from ATP to ADP is extremely crucial for supplying energy
for life processes and impacts the amount of free energy available to DO WORK
(see side section below!). Just cutting one bond provides about 7.3
kilocalories (calories as we know them) per molecule, or 30 kilojoules. This is
about the same as the energy supplied in a single peanut!!!
Our body creates ATP from the
food we eat and it relies on a host of catabolic reactions – triggered and
carried out by hormones and neurotransmitters – to effectively “sense” and keep
ATP levels steady in all cells. Here is
a quick side note, and then we will start our journey from mouth to energy to
see how the food we eat becomes ATP. This discussion will focus on carbohydrates.
THINK IT, SHARE IT: GIBBS
FREE ENERGY AND HOW YOU CAN BE AS SMART AS YOUR BODY.
Gibbs Free Energy is a really complex concept, however, the
idea is simple. Basically, it is the energy that is applied to do work. In our cells, we keep ATP in a concentration
that is NOT at equilibrium. The phosphate bonds, although high in energy, are
not as strong as hydrogen bonds. When ATP is present in unbuffered water
(normally charged water), the bonds in ATP will break down to ADP plus a free P
(phosphate group). [Can you guess what ADP stands for….??] Thus, the system
does not strive for equilibrium between ATP and ADP, rather, the charge of the
system must keep ATP to ADP at a 10:1 ratio in an aqueous solution. This means
that there is always some “undone” work in the system, this allows for the
input of more energy. Too much undone work causes an imbalance, and too little
causes the finished product to be degraded.
How does this affect your life?
Have their been times in your life when you’ve strived for equilibrium rather
than excellence? It’s easy to get lost in the mess of wanting to be great at a
host of things or to a host of people. The flux of free energy that is gained
by keeping things out of equilibrium allows for greater improvements in a constant
system.
Ok. So we know that food gives us energy. Energy in the body
is known as ATP. Now comes the nutritional aspect as we discuss how
CARBOHYDRATES, FATS, and PROTEINS are used to make ATP. We will also discuss
the difference between AEROBIC and ANAEROBIC metabolism because, believe it or
not, there was a time when organisms had to (and some still do) survive in an
environment lacking oxygen.
CARBOHYDRATES: THE
“C” WORD OF DIETERS
Damn you bread and pasta for being so delicious!! But
wait…there is a reason why our body craves carbohydrates. They give us the
fastest, most readily available source of energy. Back in times when we didn’t
sit all day, we needed this energy to catch our food. Besides the occasional
street fight outside of your local Whole Foods, we don’t typically put that
much work into food nowadays.
Carbs are broken down by enzymes in your body to their most
bare form – monosaccharides. A di-saccharide is something like sucrose, which
is table sugar (glucose and fructose), and a polysaccharide is a long chain of
carbohydrate molecules (typically glucose) . The bonds between these molecules
must be broken before the enzymes that help us create energy can come into
play. Because disaccharides such as table sugar have less bonds to break, they
are able to release energy faster than polysaccharides. This is why a piece of
candy is called a simple sugar and a piece of bread is called a complex
carbohydrate. The addition of fiber and protein in complex carbohydrates also
slows the digestion and has a more gradual impact on blood sugar and hunger
levels.
Once the bonds between individual monosaccharides are
broken, the monosaccharide – glucose, in most cases – enters the energy
releasing pathways. That’s right, pathways. This shit is going to get a bit
tricky, so take a breather here if you need to and come back. This is the
exciting part.
GLYCOLYSIS
The glycolytic pathway is one of the most ancient pathways
for creating energy that we know of. Why? It is ANAEROBIC – it takes place in
the absence of oxygen. It is highly conserved in both prokaryotes and
eukaryotes. It is what was essential in the oxygen-poor atmosphere of
pre-eukaryotic Earth.
Glycolysis literally means “breaking apart” glycogen. Glycogen
is a storage form of glucose, and in this sense, it is glucose. We will talk
about glycogen at another time when we talk about weight management and why you
gain weight when you eat too much.
In glycolysis, an enzyme breaks glucose down into 2, 3-carbon
molecules called pyruvate. Remember that glycolysis is anaerobic, but it
is the first step of celluar respiration regardless of whether there is oxygen
or not.
-----
WITHOUT OXYGEN…pyruvate is broken down into lactic acid.
You know when you work out super hard and your muscles burn?
Skeletal muscle requires ATP. If you don’t have enough oxygen in your body to
support how much ATP you need, its broken down into lactic acid and you get
that “burn”. Lactic acid CAN be converted back to glucose through a process in
the liver known as the Cori Cycle. Google it, it’s pretty cool.
You get 2 ATP (not taking into account Gibbs Free Energy*)
with glycolysis alone.
------
WITH OXYGEN…pyruvate enters the citric acid cycle and
oxidative phosphorylation.
Here is the quick and dirty. Oxygen is an electron acceptor.
When you cleave (break) bonds of glucose, you end up with these differently
charged molecules called NADH, NAD +, and others like it. Oxygen takes these
charges and makes energy. It’s pretty amazing, and highly detailed. Comment if you have questions or want to
learn more. This is also the time when those phosphate bonds which carry all
the energy are created in the ATP molecule.
You get 30 ATP *with glycolysis and the citric acid cycle/oxidative phosphorylation.
As you can see, the presence of oxygen makes for a much more
efficient system. However, glycolysis is able to produce ATP as well.
----
When all is said and done and ATP is synthesized, it is then
used to do things such as breathe, poop, run, think, and create red blood cells
(among a million other things). Using ATP means that ATP becomes ADP and heat
and carbon dioxide are released. This heat is what a calorie essentially is.
ADP is kept in the cell, and our body uses the food we eat to continuously
recycle ADP back to ATP.
You may be asking yourself “what the hell does this have to
do with my diet”, and I can understand that. Trust me, the discussions to come
will tie everything together. I want
your questions, your feedback, and I want you to research some on your
own.
Here are some take-away points that I want you to keep in
mind for further learning and discussion:
- The amount of calories in a food are a measure of energy that your body can create from eating that food.
- All macronutrients – proteins, carbohydrates, and lipids (fats) are able to be formed into ATP in the body
- Carbohydrates create ATP the fastest and are able to create ATP in an anaerobic system
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