I've always been perplexed as to why cyclists, with the best info and drive to take care of their bodies would put something so synthetic and harsh into their bodies. I guessed it was because of the sugar caffeine hit, but never actually came across any literature, at least not as well summarized as what plopped in my inbox the other day. I wanted to pass this great email on from Dr. Gabe Mirkin that talks about High Fructose Corn Syrup, or HFCSs, (the sugar source for so many processed drinks, foods and candies). It has a load of references stating how the combination of HFCS and caffeine work together to boost performance. But be careful, the rationale doesn't justify drinking Coke (or any beverage with HFCSs) for everyone. I can't summarize his info any better so read it in his own words below:
Sodas with HFCS and Caffeine May Be Best Drinks for Endurance
The limiting factor in endurance racing is the time that it
takes to get enough oxygen into muscles to burn food for energy.
Anything that reduces oxygen requirements allows you to race
faster. Sugar stored in muscles, called glycogen, requires less
oxygen than fat or protein. Anything that helps you keep sugar
in muscles longer gives you greater endurance.
A study from Georgia State University shows that drinks that
contain both glucose and fructose burn more carbohydrates than
those containing only glucose, and allow cyclists to ride much
faster over 60 miles (International Journal of Sport Nutrition and
Exercise Metabolism, April 2010).
Most soft drinks are sweetened with high fructose corn syrup
(HFCS). Both HFCS and conventional sugar (sucrose) contain a
mixture of two sugars, glucose and fructose, in nearly the same
concentrations: HFCS has 55 percent fructose/42 percent glucose,
while sucrose is a 50/50 mixture. So the relative concentrations
of glucose and fructose are not significant. However, the fructose
in sucrose from cane or beet sugar is bound to glucose and must
first be separated from it, so it is absorbed more slowly into the
bloodstream. The manufacturing process for HFCS frees the
fructose from glucose to makes it into a free, unbound form that
is absorbed more rapidly into the bloodstream. This could cause
a higher rise in blood sugar ((Pharmacology, Biochemistry and
Behavior, March 18, 2010) and provide more sugar for muscles
during exercise. We need to wait for more research to know if
HFCS drinks improve endurance more those made with cane or beet
Caffeine increases endurance (Medicine & Science in Sports
& Exercise, July 2010) by increasing absorption of sugar by
muscles (Journal of Applied Physiology, June 2006). Those who
took sugared drinks with caffeine were able to absorb and use 26
percent more of the ingested sugar than those who took the same
drinks without caffeine.
On long rides, we drink colas for their sugar and caffeine.
However, you should take sugared drinks only when you exercise and
for up to an hour after you finish(emphasis added). Contracting muscles remove
sugar from the bloodstream rapidly without needing much insulin.
Taking sugared drinks when you are not exercising causes higher
rises in blood sugar that increase risk for diabetes and cell
damage (emphasis added).
The take home message is this: what makes HFCS so effective to replenish glycogen stores during or immediately after a hard or long ride is exactly why it is so destructive at any other time. The sugars in HFCSs are absorbed so much faster into the blood than even white table sugar, resulting in such an insulin and blood sugar spike that in any other circumstance (an afternoon pick me up or to wash down lunch) it damages the insulin and sugar control mechanisms. And since the liver is what is primarily responsible for converting excess sugar into fat, it wrecks total havoc. What kind of havoc? Like the kind of damage alcoholics do to themselves, but without the alcohol. In fact, it's referred to as "non-alcoholic fatty liver disease" and is showing up exponentially in children , with the rise in consumption of highly processed foods sweetened with HFCSs high on the list of culprits.
So don't make it any harder on your liver, (and pancreas, blood vessels, etc. for that matter) by consuming HFCSs than it has to be. And if you are going to indulge yourself, at least savor it during or immediately after a long or hard ride (or run, swim, etc.)