First some terminology.
Fructose ... a five carbon sugar that occurs naturally in fruit,
does not cause as much insulin to be secreted as glucose and
tastes sweeter than glucose.
Glucose ... a six carbon sugar that is the breakdown product of
glycogen(a polymer of glucose, multiple glucose units hooked
together) that occurs naturally in potatoes and grains.
Glycogen ... multiple units of glucose hooked together (a polymer).
What is typically called "complex carbohydrate" today.
Glycolysis ... derived from the Greek stem glyk- "sweet" and
lysis meaning dissolution. The metabolic pathway for the initial
utilization of glucose.
Phosphofructokinase ... the enzyme that catalyzes the reaction of
fructose 6-phosphate to fructose 1,6-biphosphate. You don't
need to understand anything more about this reaction other
than the fact that if fructose comes from a source other than
the degradation of glucose, it blocks this step for glucose
until all the non-glucose derived fructose has
Glucose and Fructose Are Both Metabolized via Gylcolysis
Both fructose and glucose are metabolized via glycolysis.
Both end up at some point as three carbon fragments. In
order for glucose to be broken down into three carbon fragments
it must first be metabolized to a five carbon sugar, actually
fructose. This is where the trouble starts, since fructose
is already a five carbon sugar. The following analogy I
hope will aid in explaining this. The analogy, however,
is far from perfect.
Whether we start out with separate glucose and fructose as in
high fructose corn syrup or honey, or with fructose and glucose
hooked together as in sucrose(common table sugar), makes no
difference. As soon as sucrose hits the bloodstream, it is
immediately broken down (hydrolyzed) to fructose and glucose.
Freda Fructose gets married to Gary (Glucose) Sucrose. They live
happily on Sugar Lane. Both work in muscle and liver cells
where they are metabolized usually into fat and slow the
immune system to a crawl. They get up early in the morning
and both have to get on the Glycolysis Road to get to work.
Gary (Glucose) is one carbon atom heavier than Freda Fructose and because of that, he cannot cross the river on one of the lighter and faster bridges on their way to work. Freda Fructose however, being lighter, has no problem crossing the faster bridge and making the short-cut to the Glycolysis Road. Gary Glucose, however, has to get on the road well above the short-cut, since he is too heavy to take the lighter bridge short-cut.
The Phosphofructokinase Intersection
As usual Freda Fructose gets to the Phosphofructokinase
intersection well before Gary Glucose. By the time Gary
Glucose gets to the intersection, the traffic directing
policeman is once again allowing all the Freda Fructoses
to make the turn onto Glycolysis Road while, all the Gary
Glucoses can do is sit in traffic and wait. Once again,
Gary, and all the other Glucoses on their way to work,
must sit and wait for all the Freda Fructoses to get on
Glycolysis Road before they can continue.
LA Traffic Control
Traffic control sees all these Glucoses sitting stuck in
traffic, just like traffic backs up everyday in LA.
It reacts by injecting a lot of green lights (insulin)
into the pathway for the Glucoses to get to work. Finally,
all the Fructoses pass and now because there are too
many green lights, all the Glucoses pass quickly.
All of the sudden there are no Glucoses to be found on the
Glycolysis Road. All the cells along the way that used
to be able to snag some Glucose can't because there
isn't any. Whether it is the excessive insulin that is
the cause of so many of the lifestyle diseases we see today
or, all the backed up Gary Glucoses decide to cause their
own damage to the arteries they are in, I don't know.
It is however, clearly established that the ingestion of
sucrose (fructose and glucose) is related to many of our
lifestyle diseases today including the extensive damage
to the vascular system that occurs with adult onset diabetes
mellitus. I know, my damaged arteries are up on this site.
Now you begin to feel lightheaded, dizzy and a bit disoriented.
Traffic control has injected too many green lights and the
concentration of glucose drops precipitously. The brain
starts to complain because it no longer has enough glucose
to function. If the blood sugar gets low enough, serious
complications can occur.
Fructose and Glucose Together
The combination of fructose and glucose should be avoided as
much as possible. When you eat your fruit, try to allow at
least an hour or preferably two, before eating potatoes,
whole grains or rice. Also avoid as much as you can sucrose,
high fructose corn syrup, honey and maple syrup or, any
sweetener that has as it main ingredients, fructose and
Brown Rice Syrup
Brown rice syrup is roughly about 45% maltose (two glucose units
hooked together), 50% complex carbohydrates and 3% glucose. No
glucose and fructose together but still sweet and I have known
some people who can even get hypoglycemic from it.
Barley Malt Syrup
Made from whole barley it is about 65% Maltose and 30% complex
These are usually combinations of glucose, fructose and
sucrose and should be avoided.
Maple syrup is about 65% sucrose and should be avoided.
Today's Health Tip:
If you want sweet, you are safest with stevia. Next would be
sweeteners derived from rice and barley. Sucrose, high
fructose corn syrup, maple syrup and fruit juice
concentrates should be avoided.
Stryer Biochemistry Fourth Edition
Copyright John Mericle M.D. 2005 All Rights Reserved
To really get off of sweets and "deprogram a sugar-coated
palate," the MericleDiet is hard to beat. Generous servings
of organic complex carbohydrates will keep you and your
brain happy. To visit the MericleDiet follow the link below.
One of our readers Wendy in the UK writes:
Just to let you know that according to the website below that
takes you to Carol Bond Health Foods it is spelt Stevita. I
couldn't find it anywhere on the site and through asking
the chat section it was spelt differently. Thought you would
like to know so that you can let the other newsletter
PS Really enjoy the newsletter. Find it very informing so thank
you. Gave up drinking milk last year after reading your article!
Feel much healthier as a result.
To take Stevia for a test drive or purchase some online
follow the link below. I had luck just searching stevia
but you could also search the product "Stevita."
Thanks for your time.
DrMericle.com is devoted to achieving optimal health and peak performance through diet and lifestyle change. Dr. Mericle brings together a unique blend of formal training in organic chemistry and biochemistry, medical education, 29 marathons, 3 Hawaii Ironman competitions and a lot of practical real life experience.