It is well-accepted and well-supported that taking in carbs during endurance
training or competitions will enable an athlete to perform at a higher intensity
for a longer period of time. But, there is some confusion as to how many carbs
to recommend during exercise.
Out with the oldConventional
wisdom has long held that well-trained athletes should consume no more than 60
grams of carbs per hour during exercise. This is based on the idea that the
maximum rate at which ingested carbs can be absorbed from the digestive tract
and metabolized as energy by working muscles is about 1 gram per minute, or 60
grams over the course of an hour.
In with the newHowever, new
research from Dr. Asker Jeukendrup of the Human Performance Laboratory School of
Sport and Exercise Sciences, University of Birmingham, United Kingdom, has
toppled the conventional wisdom. A recent study published in the February 2008
issue of Medicine and Science in Sport and Exercise, the official journal of the
American College of Sports Medicine, shows that consuming a specific blend of
glucose and fructose carbohydrates improved endurance performance by an average
of 8% in trained athletes, compared to consuming the same amount of glucose
alone. It turns out that the 60-grams-of-carbs-per-hour convention was based on
research where only a single carbohydrate source, glucose, was given to
athletes. These studies were accurate in showing that glucose alone can’t be
absorbed any faster than about 60 grams per hour. But Jeukendrup and his team
fed a combination of glucose and fructose in a 2:1 ratio to endurance athletes.
And instead of topping out at 1 gram of ingested carbs per minute, the athletes
were able to absorb and metabolize about 50% more ingested carbs every minute
during exercise.
This finding is astounding if you’re an athlete faced
with tough competition where minutes or seconds off your time to finish can mean
a medal or elimination. Instead of consuming 60 grams of carbs per hour, you can
now consume 90 grams of carbs every hour as long as those carbs are in a 2:1
ratio of glucose to fructose. To make that easy and convenient for you,
POWERBAR
® SPORT bars,
POWERBAR
® FRUIT
ENERGIZE bars, and POWERBAR
® GEL Carbohydrate
Electrolyte Blends all feature POWERBAR
® C2 MAX, the exact 2:1 blend
of glucose and fructose that was the subject of Dr Jeukendrup’s groundbreaking
research.
How does the unique carb combination work?Jeukendrup
and his colleagues believe that the glucose-fructose combination works better
than glucose alone because having multiple carbohydrate sources allows more
carbohydrate to be absorbed from the digestive tract. Research indicates that
glucose and fructose have their own separate transport systems in the digestive
tract. These transporters help carry ingested glucose and fructose from the
digestive tract into cells. However, the glucose transporter can only carry
glucose, and once it’s filled, it can’t carry any more. But the revelation is
that fructose has its own separate transportation system. So even though the
glucose transporter is filled to capacity, the fructose transporter can deliver
even more energy to working muscles. Thus, by providing both glucose and
fructose, and taking advantage of both transportation systems, you too can
deliver more energy to your muscles and extend endurance even further.
In
research just published, Jeukendrup proved the endurance advantage. He gave
trained cyclists plain water, plain water plus glucose, or plain water plus
glucose and fructose in a 2:1 ratio. The cyclists rode for two hours, then had
to complete a time trial of about one hour’s duration. When the athletes
ingested the combination of glucose and fructose, they achieved a time trial
performance that was 8% faster than when they consumed glucose alone. And
average performance time was 19% faster when the carb combination was compared
with water alone.
Easier on you, tooAnd as if that weren’t
enough good news, research also shows that this combination of carbohydrates is
better tolerated during exercise than are glucose-based products. This is good
news for athletes that have trouble tolerating carbohydrates during
exercise.
Drinks containing carbohydrates that use different transporters
for intestinal absorption seem to result in a smaller amount of carbohydrate
remaining in the intestine, and therefore, osmotic shifts and malabsorption may
be reduced. This probably means that drinks with multiple transportable
carbohydrates are less likely to cause gastrointestinal distress. Interestingly,
this finding is consistent in studies of carbohydrate-related gastrointestinal
discomfort during exercise. Subjects tended to feel less bloated with the
glucose-plus-fructose drinks versus the glucose-only drinks. The tolerance of
carbohydrate drinks and development of GI distress seems highly individual;
therefore, strategies for carbohydrate intake will always have to be developed
on an individual basis.
Carbohydrate and fluid deliveryWe
often advise athletes to avoid the intake of highly concentrated carbohydrate
solutions, because these solutions have been shown to delay gastric emptying and
fluid absorption. Although there is a lot of evidence to support this, there are
also observations that impairment of fluid delivery is minimized when
combinations of multiple, transportable carbohydrate are ingested. Fluid
delivery with a glucose-plus-fructose solution has been shown to be greater than
fluid delivery from a glucose solution alone.
Bottom line: When it comes
to counseling endurance athletes on carbohydrate intake during exercise, go with
the cutting edge. To optimize performance, recommend consumption of a 2:1 ratio
of glucose to fructose during exercise, with doses up to 90 grams per hour of
this powerful glucose/fructose energy mix. Finally, remember that POWERBAR C2
MAX helps give you that cutting-edge endurance advantage.
Disclaimer:
The scientific information found on the powerbar.com website is derived from the following sources unless otherwise stated:
American College of Sports Medicine, Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc 2007;39:377–390.
American College of Sports Medicine; American Dietetic Association; Dietitians of Canada. Joint Position Statement: nutrition and athletic performance. American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada. Med Sci Sports Exerc 2000;32:2130–2145.
Burke L, Dean V, eds. Clinical sports nutrition. McGraw-Hill Companies, Australia, 2006; 415–453.
Currell K, Jeukendrup A. Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sports Exerc 2008;40:275-281.
Jeukendrup AE, Moseley L, Mainwaring GI, Samuels S, Perry S, Mann. CH. Exogenous carbohydrate oxidation during ultraendurance exercise. J Appl Physiol 2006;100:1134-1141.
Asker Jeukendrup, Michael Gleeson: Sport Nutrition, An Introduction to Energy Production and Performance, Human Kinetics 2004
Expert Panel:
Trent Stellingwerff PhD, BSc, Senior Research Scientist – Performance Nutrition, Nestlé Research Center
Christopher D. Jensen PhD, MPH, RD Nutrition & Epidemiology Researcher
Tricia L. Griffin RD, CSSD, POWERBAR Sports Nutritionist
1. Currell K, Jeukendrup A. Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sports Exerc 40, 275–281 (2008).
2. Jentjens, R.L., Venables, M.C. & Jeukendrup, A.E. Oxidation of exogenous glucose, sucrose, and maltose during prolonged cycling exercise. J Appl Physiol 96, 1285–1291 (2004).
3. Jentjens, R.L., Moseley, L., Waring, R.H., Harding, L.K. & Jeukendrup, A.E. Oxidation of combined ingestion of glucose and fructose during exercise. J Appl P
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