[PHNUTR-L] Glycemic Index Values are Variable

[Kathrynne Holden]

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Source: Tufts University 	  	
Released: Wed 26-Sep-2007, 08:45 ET
http://www.newswise.com/articles/view/533711/?sc=dwhp

Glycemic Index Values are Variable

Description

Researchers from Tufts University reported that multiple glycemic index 
value determinations using a simple test food, white bread, resulted in 
a relatively high level of inter-individual (among different 
individuals) and intra-individual (within the same individual) 
variability. Further studies will focus on better defining the magnitude 
and the sources of the variability. The intent is to better understand 
how glycemic index relates to chronic disease risk in a range of 
individuals.

Newswise — In work investigating the reproducibility of glycemic index 
values, researchers at the Jean Mayer USDA Human Nutrition Research 
Center on Aging at Tufts University (USDA HNRCA) have reported that 
multiple glycemic index value determinations (measure of the rate of 
glucose absorption into the bloodstream) using a simple test food, white 
bread, resulted in a relatively high level of inter-individual (among 
different individuals), and intra-individual (within the same 
individual) variability. Further studies will focus on better defining 
the magnitude and the sources of the variability. The intent is to 
better understand how glycemic index relates to chronic disease risk in 
a wide range of individuals.

Alice Lichtenstein, DSc, corresponding author and director of the 
Cardiovascular Nutrition Laboratory at the USDA HNRCA and colleagues 
assessed 14 study participants’ glycemic response to 50 grams of 
carbohydrate in the form of white bread (test food) and glucose 
dissolved in water (control food) on different days. This experiment was 
repeated three times with each individual.

“Using glucose as the control food, previous studies indicate that white 
bread has a glycemic index of about 70,” says Lichtenstein, who is also 
the Gershoff professor of nutrition science and policy at the Friedman 
School of Nutrition Science and Policy at Tufts. “In our study the 
combined average was 71, virtually identical to the published value. 
However, quite strikingly, individual values ranged from 44 to 132. What 
is critical is to determine why there is such a wide range of responses 
among individuals.

In addition, within the same individual, test values varied by as much 
as 42 percent. “These results show that perhaps using glycemic index for 
groups is a reasonable indicator to predict chronic disease risk, but 
there is still considerable uncertainty when applying glycemic index to 
individuals,” explains Lichtenstein.

Glycemic index is a scale applied to foods based on how quickly the 
glucose in foods is absorbed into the blood stream, relative to pure 
glucose. Some nutrition professionals use the glycemic index as a tool 
for people trying to control blood sugar, such as those with diabetes. 
Others use the mean glycemic index of diets to predict chronic disease 
risk in large groups of people. Potential confounding factors, such as 
the fiber or fat content of the food, are not directly factored into the 
calculations.

“There are many factors that can influence the glycemic index of a 
food,” says Lichtenstein. “For example, a piece of white bread may have 
a high glycemic index but, if a person eats a slice of turkey and cheese 
with that bread, the effect of the multiple foods may result in a 
different glycemic index than if that person had eaten the white bread 
alone. Since most food is consumed as combinations during meals and 
snacks, there is a need to assess the significance of using glycemic 
index values determined on individual foods for food mixtures. 
Similarly, it is important to know whether the food consumed prior to a 
meal or snack alters subsequent glycemic response.

It is possible that we need to develop better research tools and more 
stringent applications for glycemic index determinations,” she says. 
“Larger studies of diverse populations are needed to determine why 
inter-individual, and particularly intra-individual, glycemic index 
values are so variable. If we can identify the source of the 
variability, it will allow for more insight into the applications of the 
glycemic index as a tool for both researchers and in public health 
messages.”

Lichtenstein and colleagues have received a five-year grant from the 
National Institute of Diabetes and Digestive and Kidney Diseases to 
further their understanding of the glycemic index and its utilities. The 
current study was supported by the U.S. Department of Agriculture’s 
Agricultural Research Service.

Vega-Lopez S, Ausman LM, Griffith JL, Lichtenstein AH. Diabetes Care. 
2007 (June); 30 (6): 1412-1417. “Interindividual Variability and 
Intra-Individual Reproducibility of Glycemic Index Values for Commercial 
White Bread.”

The Gerald J. and Dorothy R. Friedman School of Nutrition Science and 
Policy at Tufts University is the only independent school of nutrition 
in the United States. The school’s eight centers, which focus on 
questions relating to famine, hunger, poverty, and communications, are 
renowned for the application of scientific research to national and 
international policy. For two decades, the Jean Mayer USDA Human 
Nutrition Research Center on Aging at Tufts University has studied the 
relationship between good nutrition and good health in aging 
populations. Tufts research scientists work with federal agencies to 
establish the USDA Dietary Guidelines, the Dietary Reference Intakes, 
and other significant public policies.
-- 
Kathrynne Holden, MS, RD < fivestar at nutritionucanlivewith.com >
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