Glycemic Load Food Guide Pyramid for Athletic Performance
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Glycemic Load Food
Guide Pyramid for
Athletic Performance
Kristen M. Beavers, MPH, RD1 and Brian Leutholtz, PhD2
1
Exercise and Sport Nutrition Laboratory; 2Department of Health, Human Performance,
and Recreation, Baylor University, Waco, Texas
SUMMARY classification of CHO, as it provides desirable for athletes during sustained
relevant information for the prevention competition.
THE CLASSIFICATION OF CARBO-
and treatment of chronic disease. Since Unfortunately, classifying CHO as
HYDRATES (CHO) BASED ON
then, the use of the GI to promote simple or complex is flawed, confusing,
GLYCEMIC INDEX (GI), ALTHOUGH
weight loss, improve chronic health and inaccurate; especially when these
CLINICALLY USEFUL, MAY LACK
conditions, and fuel athletic perfor- terms are used as surrogates for GI. To
PRACTICAL UTILITY IN SPORT AS
mance has been studied by numerous begin, most foods are a combination of
THE AMOUNT OF CHO INGESTED
researchers in a variety of settings simple and complex CHO, and so this
ALSO AFFECTS CIRCULATING
(3,5,17,21,25). strict dichotomy only works for a select
BLOOD SUGAR. IN ATTEMPT TO
Other ways to categorize CHO have few food items. Furthermore, to label
CAPTURE THE ENTIRE GLUCOSE
been promoted by the food industry; simple CHO as unhealthy and com-
RAISING POTENTIAL OF DIETARY
sometimes referring to their products plex CHO as healthy is simply not
CARBOHYDRATES, THE accurate. Contrast the simple sugars
CONCEPT OF GLYCEMIC LOAD as low in ‘‘sugars’’ or ‘‘impact carbs.’’
These terms can be defined as CHO found in fruits to the complex CHO
(GL) HAS BEEN INTRODUCED TO found in foods such as pizza, fries, and
that are high on the GI, and have
INCORPORATE BOTH THE potato chips. Despite their simple
a great impact on blood glucose levels
QUALITY AND THE QUANTITY OF sugar content, fruits are considered
by causing a large release of insulin.
CHO CONSUMED. THIS REVIEW healthy foods as they provide a good
Other times CHO are reported as
DISCUSSES CURRENT RESEARCH source of select vitamins, minerals,
‘‘simple’’ versus ‘‘complex.’’ Simple
IN THE AREA OF GI AND GL, WITH and fiber. Conversely, pizza, fries, and
CHO are mono-, di-, or oligo-saccha-
EMPHASIS PLACED ON THE ROLE potato chips are less nutritious and
rides, often times referred to as the
OF GL IN GUIDING ATHLETE’S higher in fat than other ‘‘simple sugar’’
‘‘bad carbs.’’ These CHO are lumped
DIETARY FOOD CHOICES PRE, foods (such as fruit), despite their
into a broad category reported to cause
DURING, AND POST EXERCISE. ‘‘complex CHO’’ label. Using this
large, rapid changes in blood glucose
classification system Americans have
levels, followed by a greater fall in
been falsely educated to correlate
INTRODUCTION blood glucose. The end result is
simple sugars with negative health
n the 1970s, the term glycemic a temporary over production of insulin outcomes, and complex CHO with
I index (GI) was first introduced to
the nutrition community as a way
to classify carbohydrates (CHO) based
that can result in hypoglycemia. Com-
plex CHO, or the ‘‘good carbs,’’ are
polysaccharides or starches and are
positive health outcomes. Clearly,
a better system is needed to classify
and discuss CHO.
on their physiologic effect on blood usually touted as containing significant
amounts of other nutrients, including We propose classifying CHO into
glucose levels. Prior to this, CHO were
dietary fiber, making them more nutri- ‘‘refined’’ (processed foods) and ‘‘un-
(and still are), categorized based on
refined’’ (natural foods) categories.
chemical structure. Most notably, ent dense than simple CHO. Since the
Refining is a process that can apply
when stratified by chemical composi- digestion and absorption of complex
tion, CHO can be thought of as sugars, CHO foods are slower, they produce
KEY WORDS:
starches, and fibers. In clinical settings, more stable or sustained blood glucose
the GI has proven to be a more useful and insulin responses. Theoretically, glycemic load; glycemic index; athletic
nutritional concept than the chemical these responses would be more performance; nutrition; food pyramid
10 VOLUME 30 | NUMBER 3 | JUNE 2008 Copyright Ó National Strength and Conditioning Association
to simple or complex CHO. Quite or lactose, the ratio of amylopectin emphasis placed on exploiting the
literally, it is the act of removing fiber, and amylase in starch, starch-protein principles of GI and GL to maximize
nutrients, usually water, and other or starch-fat interactions, and the endogenous CHO stores, thereby min-
items contained within the food in its presence of anti-nutrients such as imizing the potential ergolytic effects
natural state. The act of refining foods phytates and lectins (5,26). In 1981, of CHO depletion (11). In the sections
typically concentrates sugars and re- Jenkins et al. produced table showing that follow, current research in this
sults in food items with a heightened GI response to 62 commonly eaten area will be summarized, with empha-
GI. Unrefined CHO are usually foods (15), and based on this research, sis placed on the role of GL in guiding
healthy, unadulterated, foods such as the concept of stratifying CHO by their athlete’s dietary food choices pre-,
fruits, vegetables, and whole grains, GI ranking was born; with a GI score during, and post-exercise.
which are lower in the GI, and result of 55 or less constituting a low GI food,
in a more flattened blood glucose 56–69 a medium GI food, and 70 or PRE-EXERCISE
response (Table 1). higher a high GI food. Previous literature has shown that
It has been argued that the GI lacks ingestion of a CHO-rich meal (~200–
GLYCEMIC INDEX VERSUS
GLYCEMIC LOAD practical utility as the amount of CHO 300 g) within four hours of exercise
By definition, GI is a ranking of foods ingested also affects circulating blood improves endurance or performance
based on their actual postprandial sugar. Thus, to capture the entire during prolonged moderate intensity
glucose-raising potential of dietary exercise (7,19,20,27) presumably due to
blood glucose response compared to
CHO, the concept of glycemic load increases muscle glycogen (10). How-
a reference food, either glucose or
(GL) was introduced to simultaneously ever, recent literature suggests that
white bread. GI is calculated by
incorporate both the quality and the when CHO is ingested during exercise
measuring the incremental area under
quantity of CHO consumed. In es- in amounts presently recommended by
the blood glucose curve following
sence, GL is a function of the GI of sports nutrition guidelines, pre-exercise
ingestion of a test food providing
a certain food multiplied by the CHO intake has little effect on metab-
50 g of CHO, compared with the area
number of grams of CHO of that food olism or on subsequent performance
under the curve following an equal
in a single serving. We believe the GL during prolonged cycling (4).
CHO intake from the reference food,
with all tests being conducted after an represents a more relative and accurate It has also been speculated that the
overnight fast. effect a food has on blood glucose. negative outcomes of CHO ingestion
GL ¼ GI/100 3 g of CHO in a given 30 to 60 minutes prior to exercise (i.e.,
Blood glucose area increase muscle glycogen utilization
after test food amount of food ð13Þ
GI5 3 100 and decreased time to fatigue) may be
Blood glucose area Proponents of the GI/GL based diets avoided by consuming a low GI food
after reference food argue that manipulating dietary pre- (24). Moreover, low GI foods may be
Simply put, GI reflects the rate of scription to include low GI/GL foods favored one hour prior to exercise
digestion and absorption of a CHO- decreases the occurrence of hypergly- because the slow digestion of these
rich food. Numerous factors have been cemia and hyperinsulinemia, both of foods results in the availability of fuels
identified that influenced the digestion which can lead to insulin resistance near the end of exercise (25).
and absorption rate of CHO rich foods, and further chronic disease. Applica-
including degree of food processing tions from this area of research were DURING EXERCISE
and cooking, the presence of fructose then extended to the athlete; with
Athletes undertaking prolonged exer-
cise are advised to consume CHO
Table 1 during the event to enhance perfor-
Refined versus unrefined foods
mance, most often as diluted liquids.
Refined Foods Unrefined Foods In general, ;1 g CHOmin21 is
advised, since this appears to be the
Cakes and cookies Brown rice
maximal rate of oxidation of ingested
Potato chips Oat bran CHO (5). Although it would make
sense that CHO consumed during
Candy bars Oatmeal
exercise should be easily digested and
Jellies and jams Whole grain pasta absorbed to provide a rapid supply of
energy (8), the effect of the GI and GL
Fruit beverages Wheat bread
of CHO rich foods/drinks during
Sodas Fresh fruits exercise has not yet been systemati-
cally studied. That being said, many
Salad dressings with added sugars Fresh vegetables
athletes choose CHO sources,
Strength and Conditioning Journal | www.nsca-lift.org 11
Glycemic Load Food Guide Pyramid for Athletic Performance
including specially manufactured immediately post exercise (23). In prolonged exercise. During this study,
sports drinks and bars, which would a recent study by Levenhagen et al., eight trained male athletes participated
be classified as moderate to high in GI ten subjects were used in a crossover in a crossover design composed of two
or GL (13). Moreover, low GI/GL design to examine the protein dynam- trials separated by at least seven days.
foods tend to cause more stomach ics of early vs. late macronutrient post- In both trials, subsequent to an over-
distress and are avoided during exer- exercise supplementation (18). The night fast, subjects completed a 90
cise. Studies need to be undertaken to same oral supplement (10 g protein, 8 minute run at 70% VO2max, with meals
determine if low GI/GL CHO are g CHO, 3 g fat) was administered for provided thirty minutes and two hours
advantageous over high GI/GL CHO both trials, either immediately or three following cessation of exercise. Follow-
before and during exercise. hours post-exercise. Markers of protein ing the ingestion of the second meal,
synthesis were measured, and results serum insulin concentration was higher
POST EXERCISE showed that post-exercise ingestion of in the high-GI trial as compared to the
Previous literature has shown that the a combined CHO and protein supple- low GI trial. Results suggest that a low
highest rate of muscle glycogen storage ment does enhance protein accretion. GI diet may be more beneficial for
occurs during the first hour after Authors speculate that this finding is continued utilization of fat during the
exercise (14,16). Moreover, the most due largely to the presence of circulat- later recovery period (22).
important dietary factor in glycogen ing insulin, which increases in blood
recovery during this immediate post- immediately after CHO ingestion, and DISCUSSION
exercise period is the amount of CHO is critical in the regulation of protein In 2004, Burke and colleagues put forth
that is consumed, with an intake of synthesis (2) and proteolysis (12). revised guidelines for the intake of
;7–10 g kg21 body mass providing The GI of the CHO consumed later in CHO in the everyday or training diets
maximal daily glycogen storage (9). the post-exercise period, has also be of athletes (6). These recommenda-
These findings inherently lend them- show to be important because of their tions focus on the practical application
selves to high GL foods, regardless of influence on substrate oxidation. In of substrate utilization research. As an
GI rank. Additionally, high GI CHO 2005, Stevenson et al. conducted extension to this work, we feel that
consumed together with protein have a study to examine the metabolic recommendations for the intake of
been shown to enhance exercise- responses to high GI or low GI meals CHO in terms of GL would prove
induced muscle formation when given consumed during recovery from a useful tool for the athlete or
Figure 1. The Glycemic Load Food Guide Pyramid for Athletic Performance.
12 VOLUME 30 | NUMBER 3 | JUNE 2008
professionals working with athletes. may change in the non-fasted state is of 4. Burke, LM, Claassen, A, Hawley, JA, and
We have begun this process by merg- critical importance to the athlete. Noakes, TD. Carbohydrate intake during
prolonged cycling minimizes effect of
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uct being The Glycemic Load Food cifically engineered for the athlete. Glycemic index–a new tool in sport nutrition?
Guide Pyramid for Athletes (Figure 1). Previous studies assessing the effect Int J Sport Nutr 8: 401–415, 1998.
This tool is designed to be used in the of low glycemic foods on athletic 6. Burke, LM, Kiens, B, and Ivy, JL.
lay literature to help athletes and performance have historically chosen Carbohydrates and fat for training and
professionals working with athletes lentils – often consumed in very large recovery. J Sports Sci 22: 15–30, 2004.
understand how to apply the concept portions - which may not be a practical 7. Chryssanthopoulos, C, Williams, C,
of GL to optimal athletic performance. choice for the athlete for myriad Nowitz, A, Kotsiopoulou, C, and Vleck, V.
Because numerous methodological reasons. Although low GI/GL pre- The effect of a high carbohydrate meal on
problems exist in the definition of GI competition meals have been shown to endurance running capacity. Int J Sport
and GL, including poor standardiza- prolong endurance during strenuous Nutr Exerc Metab 12: 157–171, 2002.
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variability, (1) it was paramount to use distress, the athlete is unlikely to follow index concept in carbohydrate metabolism.
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which to base our recommendations. 9. Costill, DL, Sherman, WM, Fink, WJ,
In 2002, Foster-Powell et al. published Maresh, C, Witten, M, and Miller, JM. The
Kristen M. role of dietary carbohydrates in muscle
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