Glycemic Index Could be an Unreliable
Indicator of Blood Sugar Response
by Shirley Johanna on
September 8, 2016 at 12:29 AM Diabetes News - E
The glycemic index of food may vary by
an average of 20 percent within an individual and 25 percent among individuals,
according to a study by scientists from the Jean Mayer USDA Human Nutrition
Research Center on Aging (USDA HRNCA) at Tufts University. The glycemic index
is a value that aims to quantify how fast blood sugar rises after eating.
In randomized, controlled, repeated
tests involving 63 healthy adults, researchers found that individual blood
sugar responses after consuming a fixed amount of white bread could range
across all three glycemic index categories (low, medium, or high). Part of this
variability could be attributed to insulin index and baseline HbA1c levels,
which reflect long-term glucose control--evidence that glycemic index values
are influenced by an individual's metabolic responses to food.
Developed as a way to help diabetic
individuals control their blood sugar, the glycemic index is intended to
represent the inherent effect food has on blood sugar levels. However, glycemic
index is becoming used for broader purposes such as food labeling, and has
served as the basis for several popular diets.
To study whether glycemic index values
are accurate and reproducible, Matthan and her colleagues recruited 63
volunteers, who underwent six testing sessions over 12 weeks. Volunteers fasted
and abstained from exercise and alcohol before each session. They then consumed
either white bread, a simple carbohydrate that served as the test food, or a
glucose drink, which served as a reference control, in random order. Each
contained 50 grams of available carbohydrate. Blood glucose levels were
measured at multiple time points for five hours after eating, and glycemic
index was calculated by standard formulas.
The team found that the average
glycemic index value of white bread for the study population was 62, placing it
in the category of a "medium" glycemic index food.
However, deviations averaged 15 points
in either direction, effectively placing white bread in all three glycemic
index categories. It would be considered a low glycemic index food (average
values of 35 to 55) for 22 of the volunteers, intermediate glycemic index (57
to 67) for 23 volunteers, and high glycemic index (70 to 103) for 18
volunteers. Even within the same individual, glycemic index values could differ
by more than 60 points between trials.
The variability in glycemic index
values occurred despite sample sizes larger than required by standard
calculations. The study cohort of 63 individuals far exceeded the ten
individuals used by typical glycemic index methodology, as did the six feeding
challenges and five-hour blood glucose measuring window.
The authors note their findings do not
suggest that a high glycemic index food may be healthy, or that a low glycemic
index food unhealthy. Both glycemic index and glycemic load--a value that
adjusts glycemic index to serving size--reflect only food containing
carbohydrates, and no one eats food in isolation. The high variability of
glycemic index and glycemic load reveal limitations in their clinical and
public health applicability, and glycemic index estimates and subsequent
associations with chronic disease risk needs to be reconsidered, say the
authors.
"Based on our results, we feel
strongly that glycemic index is impractical for use in food labeling or dietary
guidelines at the individual level," Matthan said. "If your doctor
told you your LDL cholesterol value could vary by 20 percent, it would be the
difference between being normal or at high risk for heart disease. I don't
think many people would find that acceptable."
By
Dr. A. Praveena
Assistant Professor
Department of Biochemistry
No comments:
Post a Comment