Carbs and Glycogen
By Gary Zeolla
Types of Carbs and Glycogen Replenishment
Carbohydrates come in three basic forms: monosaccharide, disaccharides, and
polysaccharides. Monosaccharide's are simple sugars like fructose and glucose.
Disaccharides are sugar molecules comprised of two simple sugars. Sucrose is one
such example, which is comprised of one molecule of fructose and one molecule of
glucose. Polysaccharides are also known as complex carbohydrates or more
popularly starch. Complex carbs are long chains of glucose molecules.
Carbs serve three main functions in the body. First, they can be immediately
burned for fuel. Second, they can be stored as glycogen in the liver and
muscles. Third, they can be stored as body fat.
Looking at point two, all carbs are not equal when it comes to glycogen
replenishment. "Supplements composed of glucose or glucose polymers are the most
effective for replenishment of muscle glycogen, whereas fructose is most
beneficial for the replenishment of liver glycogen" (Ivy). So glucose can be
used to replenish muscle glycogen while fructose cannot. And glucose sugar or
complex carbohydrates would both be possible sources of muscle,
glycogen-replenishing carbs. However, of these two, complex carbs would be much
… complex carbohydrates … are more effective in replenishing glycogen stores
than simple sugars. This makes sense because complex carbs are released slowly
whereas simple sugars are released very rapidly, potentially overwhelming the
glycogen synthesis pathways and "spilling over" into fat stores. Furthermore,
the increased insulin release resulting from simple sugars causes more of the
sugar to be converted to fat (Parillo, p.20).
I experienced this problem of simple sugars "spilling over into fat stores."
When I was using dextrose (a.k.a. glucose) in my post-workout drink, I began
gaining fat and feeling like my metabolism was slowing down. I was eating less
and less but still gaining weight. But when I switched to maltodextrin (a
complex carb), the problem reversed. I detail this experience in my article
I recently had someone email who had the same experience. He was gaining weight
and eating less but couldn't figure out why. But then he came across my article
and switched from dextrose to maltodextrin in his post-workout drink, and
immediately he began losing the body fat he had gained.
So maltodextrin would be much preferred to dextrose in a post-workout drink. An
even better option would be brown rice syrup.
Brown rice syrup is an extremely versatile and relatively healthy sweetener
which is derived by culturing rice with enzymes to break down the starches, then
straining off the liquid and cooking it until the desired consistency is
reached. The final product is roughly 50% soluble complex carbohydrates, 45%
maltose, and 3% glucose. The glucose is absorbed into the bloodstream
immediately, the maltose takes up to one and a half hours to be digested, and
the complex carbohydrates take from two to three hours, providing a steady
supply of energy. Rice syrup has a shelf life of about a year, and once opened,
should be stored in a cool, dry place (International Starch Institute).
Maltose is a disaccharide composed of two glucose molecules, so all of the carbs
in brown rice syrup can be used to replenish muscle glycogen. And with both the
maltose and complex carbs being metabolized slowly, this ensures maximum muscle
glycogen replenishment and minimal fat storage.
As an added bonus, brown rice syrup retains the naturally occurring nutrients in
brown rice. Brown rice syrup can be found at most health food stores. But the
one problem with brown rice syrup is it requires a blender or Vitamix to blend
the post-workout drink. Since I set up my home gym, I've been able to use brown
rice syrup, and I've found it superior to maltodextrin. But if you can only use
a shaker cup, then maltodextrin will have to do.
For times other than immediately post-workout, grains and starchy vegetables
like potatoes and corn would be ideal sources for replenishing muscle glycogen
as they contain primarily complex carbs.
Moreover, since carbs that are released slowly are more likely to be used for
glycogen replenishment than fat formation, whole grains would be preferred over
refined grains. Whole grains, especially stone-ground grains, tend to have lower
glycemic ratings than refined grains. Similarly, sweet potatoes and corn have
lower glycemic ratings than white potatoes.
That said, an important point to note is, "… the amount of glycogen you can
store is quite limited. The upper limit is generally believed to be 250-400
grams, depending on the amount of skeletal muscle you have" (Parillo, p.20).
So it doesn't take a lot of whole grain or starchy vegetable consumption to
fully replenish glycogen stores. What this means is once glycogen stores are
fully replenished, any additional carbs, if they are not immediately burned for
energy, will be stored as fat. So high-carb foods like whole grains should only
be consumed in moderation.
But exactly what "moderation" means will vary from person to person. The more
active a person is, the more their glycogen stores will be depleted and thus the
more complex carbs they can consume before glycogen stores will be filled and
the body will begin to lay down fat. The ideal would be to consume just enough
carbs for immediate energy purposes and to replenish glycogen stores, but no
Soft Drinks, Sugar, and HFCS
The primary carb source in carbonated and non-carbonated soft drinks is sugar
(sucrose) or high fructose corn syrup (HFCS). Both of these are nothing but
"empty calories." This in itself makes the consumption of such drinks unhealthy.
But soft drinks are also problematic when it comes to the issue of glycogen
To review, the body can use glucose to replenish muscle glycogen, but it cannot
use fructose. Fructose can only be used to replenish liver glycogen.
Also, sucrose is a disaccharide consisting of one molecule of glucose and one
molecule of fructose. "HFCS consists of 55 percent fructose blended with 45
percent glucose" (Challem). So only half of the carbs in sugar and a little less
than half of the carbs in HFCS can be used to replenish muscle glycogen.
Moreover, to summarize a rather complex situation, when a person exercises, the
glycogen is depleted from the muscles that are being utilized. If the person
then consumes complex carbs, the bonds between the glucose molecules will be
broken down; the liver will then allow the glucose to pass through to the
muscles until muscle glycogen stores are replenished. In this way, muscle
glycogen will be available to provide energy for the next workout. The liver
will then use any additional glucose from complex carbs to replenish its own
glycogen stores. Once both muscle and liver glycogen stores are full, any
additional carbs consumed will be stored as body fat.
However, an entirely different situation exists when fructose is consumed. Since
fructose cannot be used to replenish muscle glycogen, there is no reason for the
liver to let it pass through to the muscles. Instead, the liver will use the
fructose to replenish its own glycogen stores. Once those stores are full, any
additional fructose consumed will be converted into body fat. But the muscle
glycogen will remain depleted, so there will be no energy available, and the
exerciser will most likely drag through the next workout (summarized from
Parillo, pp. 19-21).
Be sure to note the most important point here, "… once liver glycogen stores are
full, the liver says, ‘We've got all the glycogen we can hold, so any more carbs
coming in here we'll just convert to fat'" (Parillo, p.22).
In other words, if after a hard workout the exerciser consumes a large amount of
fructose, say in the form of a large soda, the liver stores of glycogen will be
filled rather than muscle glycogen. Even the glucose in soda will most likely
not be used for replenishing muscle glycogen since soda is metabolized too
Then later, with the liver glycogen stores filled, even if complex carbs are
consumed, those carbs will not be used to replenish muscle glycogen. They will
instead be converted into body fat. Meanwhile, the muscle glycogen stores will
remain depleted. And once again, come the next workout, the exerciser will drag
though the workout.
If this pattern continues, rather than becoming more lean and muscular from
exercise and gradually increasing in endurance capacity, the person will most
likely gain body fat and continue to drag through the workouts. And with no
results forthcoming, the person very possibly give up on exercise altogether.
But the problem will not be with the workout program but with the person's
The bottom line of all of this is that sucrose and HFCS are much more likely to
be stored as body fat than complex carbs. Of course, this discussion does not
relate to just soft drinks. It would apply to any food that is high in sucrose
or HFCS content, such as cakes, cookies, pie, ice cream, candy, and the like.
If a person's diet consists of high amounts of sucrose and HFCS from any of
these sources, that is a perfect prescription for the laying down of body fat
and reduced energy levels.
Fruit is rightly promoted as being a very healthy food. Most fruits contain a
high nutrient, phytonutrient, and antioxidants content, and there is a wealth of
scientific evidence of the benefits of fruit consumption. But there are some
detractors who argue against the consumption of fruit. And their detractions
relate to the above information.
The first argument is based on fruit's high sugar content. It is said that sugar
of any sort is not good for you, even when it occurs naturally in fruit.
Moreover, it is said that fruit today has higher sugar contents than yesteryear
due to hybridization practices.
The latter is true. All you have to do is compare the size and sweetness of an
apple growing in the wild with an apple found at a grocery store. The grocery
store apple most likely will be larger, have a brighter and more consistent red
color, and most importantly, be sweeter. So basically, you'd have to eat two or
three wild apples to get the same sugar content as one grocery store apple.
However, this argument would not mean any fruit consumption is unhealthy. It
would simply mean to consume fruit only in moderation. In other words, if one
grocery store apple equals three wild apples, only eat one grocery store apple,
The second argument against fruit is more directly related to the above
discussion on glycogen replenishment. To review, glucose is especially good for
replenishing muscle glycogen but not liver glycogen. Fructose is the exact
opposite; it can be used to replenish liver glycogen but not muscle glycogen.
Fructose is also known as "fruit sugar" since fruit is the main food source of
it. So the argument of the detractors is that by consuming fruit, the athlete is
"wasting" carb intake on a form of carbs that cannot be used to replenish muscle
glycogen. This will in turn lead to lower glycogen storage and lowered exercise
performance. Moreover, "Instead of being stored as glycogen, fructose gets
directly converted to fat by the liver" (Parrillo). For this reason, fruit
should be avoided.
However, there are some problems with this reasoning. First, the sugar in fruit
is not pure fructose. All fruits in fact contain a mixture of fructose, glucose,
and sucrose. The exact amounts of each vary for different fruits, but the
popular conception that fruit is pure fructose is not correct. And the glucose
and the glucose in the sucrose could be used for muscle, glycogen-replenishment.
Add to this the fact that the rate at which fruit is digested is slower than
soda or desert foods. This is due to the high fiber content of fruit, This
slower digestion would increase the likelihood the glucose in fruit will be used
to replenish muscle glycogen and lessen the chance the sugar in fruit will be
stored as body fat.
Moreover, the amount of sugar in fruit is not really that great. It is far less
than that found in soft drinks or desert foods. For instance, one average apple
contains about 20 grams of carbs while one slice of double-layer chocolate cake
with chocolate icing contains over 100 grams of carbs (DietPower).
In addition, out of the total amount of carbs that an athlete would consume in a
day, the fructose from a couple servings of fruit would be a very small
percentage and thus would have minimal effect on lowering muscle glycogen
Or to put it another way:
… don't be deterred from eating fruit because it contains fructose. Although
fruit contains a high percentage of fructose, the total amount is relatively low
because the total amount of carbohydrate is relatively low … This is in contrast
to cake or cookies, which contain tremendous amount of sucrose (remember,
sucrose is made up of half glucose and half fructose). Therefore, although
desert foods may contain a lower percentage of fructose than fruit does, they
yield a greater amount of fructose per ounce (Faigin, p. 145; italics in
Moreover, while foods like soft drinks and desert foods are nutritionally
worthless, fruit contains a wealth of nutrients, so fruit is a much better way
to satisfy your sweet tooth than the consumption of those foods. So eat fruit.
It is a healthy food. Just don't overdo it. As the saying goes, all things in
Challem Jack, The Nutrition Reporter™ – http://www.thenutritionreporter.com/fructose_dangers.html
DietPower software. Copyright 1992-2004 by DietPower inc.
Faigin, Rob. Natural Hormonal Enhancement. Extique Publishing: Cedar Mountain,
Food Resource, Oregon State. Flavor and Flavor Components: Sweetness - http://food.oregonstate.edu/flavor/sweet.html
Ivy JL. Glycogen resynthesis after exercise: effect of carbohydrate intake. Int
J Sports Med. 1998 Jun;19 Suppl 2:S142-5. PMID: 9694422.
Parrillo, John. "Fructose: The Ideal Carbohydrate Source for Gaining Fat." John
Parrillo's Performance Press, pp.18-23.