Written by: Whitney Boland
Posted: Tuesday, 13 May 2008
At first glance, using the glycemic index might sound like
another nutritional phenomena that could be shelved next to the Zone Diet,
Atkins or South Beach. However, before you nix this nutrition guideline and
catalogue it with the list of growing diet trends and passing food faux pas,
take another look at what’s on the menu and how you as an athlete can benefit.
The Facts
The glycemic index (GI) is a scale that ranks the effect of glucose
on your body by measuring how fast it raises your blood sugar level and assigns
it a number (0-100). While the index was originally designed for diabetics,
sports nutritionists found they could gauge a food’s GI effects on athletes.
“Athletes commonly eat foods solo, a banana, a bagel,” says
Boston-based Nancy Clark, MS, RD, CSSD and author of Nancy Clark’s Sports
Nutrition Guidebook. “Hence exercise scientists became curious about the
possibility that quick or slow carbs impact exercise performance because they
affect blood glucose in different ways.”
These findings helped establish the glycemic index as a
useful tool for maximizing energy levels during exercise by indicating what to
consume at what time. Some foods, like white bread, are known to quickly raise
GI levels, while others, like lentils, are known to maintain low blood sugar
levels. Translation: your GI level could very likely affect your athletic
performance. So how do you know when to eat what, and why?
The Logistics
Eric Hörst, climbing-training expert and author of Training
For Climbing and Conditioning For Climbers, says a good rule of thumb is to
consume “low- and mid-GI foods before and during climbing/training, then high
GI foods immediately afterwards (to speed recovery), followed by a taper back
to mid- and low-GI foods” if another workout is scheduled within 24 hours.
This kind of glycogen loading is especially important for
endurance sports and those with rigorous daily training schedules to maintain
consistent energy long before you mount your bike, tie in for a climb or eject
the start line of a race.
“The consumption of carbohydrates in the hour before
exercise can help increase glycogen stores and raise blood glucose and insulin
levels,” says John Ivy, exercise physiologist at the University of Texas and
author of The Performance Zone, and it “will help jump-start the fueling
process.”
Consuming low-GI foods prior to exercise will help you
maximize this energy. Some athletes, however, might be sensitive to certain
foods. Clark suggests you “go by what feels good for your stomach.”
“Continue to consume low- to mid-GI carbs during exercise,”
says Hörst—like a sports drink, gel, or granola bar—to keep a steady flow of
nutrients and energy and help maintain the stores. According to Ivy, by doing
this, “there is less likelihood of having a rebound hypoglycemic response.”
Unlike low-GI foods, high-GI foods will spike your blood
sugar; the higher the GI levels, the quicker they raise blood-sugar levels.
When blood-sugar levels are spiked the athlete might at first experience a jolt
of energy, but that will undoubtedly be followed by “hitting the wall” or
“bonking” when energy levels drastically drop.
While it’s not advised to eat high-GI foods before a
workout, at the end of a workout it’s important to replenish the muscles as
quickly as possible during a 45-minute time period after intense exercise known
as the “glycogen window.”
According to Ivy, intense exercise quickly uses up muscle
glycogen stores, and it’s “important to replenish muscle glycogen as fast as
possible.” Ivy suggests trying “a supplement of carbohydrates (high glycemic)
plus protein. It will increase muscle glycogen synthesis faster than
carbohydrates alone…and will limit muscle tissue breakdown that occurs with
hard exercise.”
Bob Seebohar, MS, RD, CSSD, CSCS and sports dietician at the
U.S. Olympic Committee, has been working with athletes for the past 10 years.
He says it “somewhat depends on the sport and the specific energy systems used,
but in general, having ‘slower burning’ (lower GI) fuel before a competition or
training session is a benefit to almost any athlete, while ‘faster burning’
(higher GI) fuel during a competition or training session is beneficial in
order to maintain blood sugar and prevent hypoglycemia.”
Is the Glycemic Index for Everyone?
While many athletes adhere faithfully to the parameters of
the glycemic index while training, some believe that what works in theory
doesn’t always translate. Clark suggests that there are too many grey areas and
variables in the glycemic index, and claims it’s a “false scale.” How much you
eat, the food’s preparation, hot or cold, and where it was grown are only a few
of the things that factor in when determining GI. What’s more, response to
carbs can vary not only from person to person, but throughout the day. “It’s
better to experiment with different foods,” says Clark, and then decide what
works for you.
In the end, diet choices are yours. The GI rating can create
a good guideline to follow, but ultimately you’re the boss of what goes into
your body.
So you want to experiment, but don’t know where to start.
Unfortunately, glycemic indexes are not all intuition. Often foods you think
might have a low GI end up being high. Here are some examples of what to eat
and when.
Low and Slow—Eat within one hour of your workout:
• Apple
•
Spaghetti
• Lentils
•
Low-fat milk
• Yogurt with fruit
The Midline—Intake during exercise to keep a constant flow
of energy. A sports drink might be a better choice for someone who might be
sensitive to solid foods during exercise. Other foods include:
• Carrots
•
Figs
• Oatmeal
•
Granola bar
• Juice
Sky High—Consume post-exercise to quickly replenish lost
stores of glycogen:
• Bagel
•
Baked potato
• Waffles
•
Rice cakes
This summer the newest sport in the Olympics will see 25 of the world’s best swimmers racing 10K around the flat-water Beijing Olympic rowing course. 
