Why high GI carbohydrates should be
ingested after exercise to restore depleted glycogen stores.
This
article will compare which carbohydrates on the GI scale are best to ingest after exercise to receive optimal results. If
you are an athlete, not trying to cut weight or lose fat then optimal results in a nut can be defined as: gaining lean
muscle mass. Stressing muscles beyond what they are used to correlates to the muscles compensating to the new stress by becoming
stronger and bigger.
Stronger and bigger muscles means the person is burning more
calories. Burning more calories means your metabolism has been raised, which correlates too less fat being stored (everybody
loves the thought of storing less fat) Muscles can only get bigger and stronger when there is sufficient glycogen in the muscles
themselves to produce ATP (Hatfield, 1987). ATP adenosine triphosphate is the chemical in your body that allows your muscles
to contract; it’s the only substrate that can perform this task. From a workout stand point this speaks volumes in terms
of getting optimal results. If you can’t contract muscles
fully your workouts will suffer greatly. So the question arises, what is the best source of carbohydrates to ingest after
a workout.
The following study regarding high GI foods make the claim
that, following a workout ingesting foods or drinks considered high on the GI index will produce greater amount of glycogen
in the exhausted muscles opposed to foods considered low on the GI chart. Worked out muscles crave glycogen and the following
study suggest that, there is a window of opportunity which is estimated to be 1-2hrs after a workout secession to consume
carbohydrates. Our body releases the hormone insulin in the presence of carbohydrates and insulin will do one of two things.
Insulin can inject the digested carbohydrate molecule into a muscle cell for latter use as energy (the best scenario out of
the two) or it can cram the molecule into a fat cell (the worst scenario of the two). If we continue to eat carbohydrates
but never empty our glycogen stores then the carbohydrates will be stored as fat.
First, a little background is needed regarding slow and fast digesting carbs.
The GI index began with Dr. David Jenkins who was a professor at the University of Toronto, Canada. Dr. Jenkins was experimenting
to determine which carbohydrates were best for diabetic patients. He found that not all carbohydrates were created equal.
Carbohydrate foods that were metabolized quickly and produced a rapid rise in blood glucose were considered high on the glycemic
index. On the flip side carbohydrates that are metabolized more slowly, releasing glucose gradually into the blood stream
are considered low glycemic foods. The ranking of carbohydrate foods is based on a scale from 0-100- pure glucose is set at
100; other foods are ranked according to glucose. The ranges are as follows low GI foods are considered below 55: some
examples are oatmeal, yams and spaghetti. Foods that are considered intermediate GI foods are ranked 55-70 some examples are
baked potato, sweet corn and waffles. Foods considered high on the GI chart are considered 70-100 these are bananas, white
bread and honey (Miller., et al 1999). You can see how this ranking is a benefit to those suffering from diabetes (especially
insulin-dependent diabetes). There is a wave of new diets based on the GI index which postulates that high GI foods will cause
fat accumulation. As stated above these carbohydrates will be stored as fat cells only if muscles cells are full of glycogen,
and if the different body systems don’t need the apparent glucose (especially those high on the GI).
According to a study conducted by (Burke et al. , 1993) foods that are considered
high on the GI index(above 70) provided the most rapid increase in storing muscle glycogen compared with foods registering
low on the GI index (below 55).
Five well trained cyclists embarked
on an exercise trial to deplete muscle glycogen in vastus lateralis muscles. The cyclist cycled for 2hr at 75% of maximal
VO2 uptake (max VO2 is the maximal amount of oxygen that can transported to your body’s tissues from
your lungs) followed by four 30s sprints on two occasions one week apart. Upon the completion of each trail the subjects rested
and ingested a diet composed of entirely carbohydrate foods. One trail composed carbohydrates with a high GI and for the other
trail the carbohydrates were low GI. Total carbohydrates intake was 10g/kg of body mass. The carbohydrate diet was distributed
between four meals at 0, 4, 8, and 21h post exercise. Blood samples were taken before any exercise bout started, immediately
following exercise and before each meal. Blood samples were drawn from the vastus lateralis immediately after exercise and
after 24hr.
The results were as follows glucose and insulin levels after
each meal were greater (p< or=0.05) for the high GI meals than for the low GI meals. There was also a significant increase in muscle glycogen
content after 24hr of recovery (P=0.02) with the high GI diet (106=/_11.7 mmol/kg wet wt) than with the low GI diet (71.5=_6.5
mmol/kg).
Again if you are looking to restore glycogen
levels for killer workouts and are not concerned about cutting
weight for a particle sport then foods high on the GI chart immediately after exercising is the way to go.
I personally eat anyone of the following after working out: bagels, white bread, potatoes or white rice. I, then wait about
30-45 min before ingesting my protein usually a whey shake. The 30-45 wait periods allows the insulin levels to sky rocket
without being slowed down by the protein. The high levels of insulin allow the protein to be piggy backed right into the muscles.
Amino acids and glycogen going into a starved muscle equals one thing= INCREDIBLE
RESULTS.
“If you are not at the
front of the dog sled team, the view never changes”
-Unknown
Reference: Miller,
J. B. , Wolever, T. , Colagiuri, S. , Powell, K. (1998). The Glucose Revolution.
New York, NY: Marlowe & Company.
Hatfield, F. C. (1987).
Ultimate Sports Nutrition. Chicago, IL: Contemporary Books.
Gropper, S. S. , Smith, L. J. , Groff, L. J. (2005). Advanced Nutrition and Human Metabolism. Belmount,
CA: Thomson & Wadsworth.
Burke, L. M. , Collier, G. R., Hargreaves, M. (1993). Muscle
Glycogen Storage After Prolonged Exercise: Effect of the Glycemic Idex of Carbohydrates Feedings. Journal of Applied Physiology, 75, 1019-1023.
