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CARBOHYDRATES
Carbs are the primary source of fuel for the body, (unless of course you are
following a ketogenic low carb diet) but before they can be absorbed and utilised
by the cells in the body they must be broken down into a more manageable form,
eg, monosaccharides (one single sugar molecule) such as glucose. The ultimate
source of glucose is sugars and starches, natural reserves of which are created
by energy from the sun, carbon dioxide and water.
Glucose is a vital component of the human body as it serves the brain and the
central nervous system. To maintain a continual consistent supply of glucose
the body stores reserves in the muscles and liver as glycogen. If you are eating
insufficient carbs these glycogen reserves are mobilised and converted back
to glucose. Once this glycogen store has been exhausted the body will start
to breakdown its own muscle to synthesise glucose. In other words, protein itself
(your skeletal muscle tissue) can be broken down into its constituents to form
carbohydrate or blood glucose known as glycogen. This sole fact demonstrates,
that although our systems are primed and geared towards eating carbohydrate
as our main energy and fuel source, this is not the exclusive form of energy.
And it is for this reason that carbohydrates are confused in many texts and
books as being essential macro nutrients. They are near essential, but life
can indeed go on without them. And they can often be classed as rather satiating
and delicious food source.
Traditionally carbohydrates have been classified in terms of chemical structure
and it was once thought that the more complex the structure of the carbohydrate,
the longer it would take to be digested, therefore, complex starch molecules
were thought to digested slowly and steadily whilst simple sugars were thought
to digest rapidly. We now know from scientific research with real foods and
real people that the concept of simple and complex carbs does not really tell
us anything about the way they will actually behave in the human body. Instead,
we now use a tool called the Glycaemic Index to tell us which foods will be
digested and absorbed rapidly and which will take longer. In response to this
rise in sugar into the blood stream, your body then produces insulin from the
glands of the pancreas and this response is measured using the insulin index.
Carbohydrates that break down quickly during digestion provide a high burst
of glucose to the bloodstream. Carbohydrates that are broken down slowly release
a steady stream of glucose into the blood. Slow, steady, digestion of foods
prevents wild fluctuations in blood-sugar, thus negating the need for the body
to break down muscle tissue to top up glucose supplies. This factor spares your
muscle tissue and assists in the anabolic process of muscle cell growth and
repair. The Glycaemic Index is a ranking of foods from 0 - 100 that tells us
whether a food will affect blood sugar dramatically, moderately or just a little.
For the majority of people most of the time, slowly digested carbohydrates are
preferable to rapidly digested carbs. However, some athletes can benefit from
in taking rapidly digesting and absorbing carbs at the right time, a topic we
shall return to later.
Slowly digested carbs release sugar into the blood stream in a slow consistent
trickle. Consequently, they fill you up and keep your hunger satisfied for longer.
Moreover, by maintaining a steady level of available glucose for fuel they enable
you to burn more of your body fat without resorting to breaking down muscle
protein for energy.
Carbohydrates are natural appetite suppressants.
When you eat a carbohydrate rich meal your body responds by secreting the hormone
insulin form the pancreas. Insulin signals the fed-state and stimulates the
storage of fuels such as glucose. The greater the rise in blood-sugar, the more
insulin produced. Glucose is stored as Glycogen in the liver and the muscles.
This storage facility, however, has a limited capacity, any excess glucose that
cannot be stored as glycogen enters the adipose (fat) cells of the body and
stimulates the production of triacylglycerides. Consequently, if an individual's
blood-sugar constantly fluctuates above the maximum storage capacity the excess
glucose that they ingest will be stored as fat. Carbs which are digested quickly
raise blood-sugar levels very high very rapidly and are therefore likely to
push glucose levels above that that can be stored by the body as glycogen. Such
foods are therefore likely to promote the storage of fat. Slowly digested carbs
raise blood-sugar levels slowly and steadily, just enough to keep supplies of
glycogen topped up without stimulating fat synthesis.
Carbohydrates and Peak Sports Performance
The rate at which glucose enters the bloodstream affects the insulin response
as outlined above. The higher the blood-sugar increase, the greater the amount
of insulin produced in general. Although this rule of thumb is sometimes negated
by recent research within the insulin index. This is although a good general
rule of thumb. As glucose is the fuel most preferred by the body, its availability
greatly affects the exercising muscle.
The primary fuel for exercise is Adenosine Triphosphate (ATP). The rate of
ATP synthesis from carbs is about 1.0 mol/min, from fats the rate is only 0.5
mol/min therefore carbs yield approximately twice as much energy as fats.
When we are talking about eating for peak sports performance, the timing of
the meal is crucial:
-Before an event
Carbs which are digested and absorbed slowly are able to provide a constant
supply of glucose to the working muscle right into the end of a workout when
the glycogen stores are running low. How do you know which carbohydrates are
going to be released slowly into your system. Well for this you need to refer
to the glycaemic index and the insulin index. Where you should be looking for
carbohydrate sources and combinations that produce little insulin and have a
low GI rating. Remember the primary fuel source used for the brain to function
and for heavy endurance activities is indeed glucose (carbohydrate). When you
are talking about higher intensity, lower volume activities like brief 40 minute
resistance workouts with weights, your body actually burns mostly intracellular
fats. This means when you are performing brief and intense weights workouts,
protein is of a more critical concern to your carbohydrate levels before a session,
and become greatly more important post your exercise session to release your
anabolic hormone insulin in order to shuttle vital amino acids back into muscle
tissue to initiate repair and of course growth.
-After an event
Quickly digested carbohydrate foods rapidly top-up the depleted blood-sugar
stimulating insulin production, the hormone responsible for storing glucose
in the muscle tissue. Any glucose eaten after an event when blood sugar is low
and stores are exhausted is therefore sent straight to the muscle where it is
used for protein synthesis and is NOT STORED AS FAT. So which carbohydrates
should you consume immediately after your training. Well you need to refer to
the glycaemic index and the insulin index. Here you want to consume high insulin
spiking carbohydrate sources and combinations that have a very high GI rating.
After an event it is important to replenish the supplies of glucose used up
during intense training. It is also a good idea to take advantage of this state
of low blood-sugar to eat foods rich in glucose as, following intense training,
glucose will be stored directly in the muscle tissue as glycogen and promote
protein synthesis and hence muscle growth.
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