Glycemic Index Is Unreliable

It is about time! High variability suggests glycemic index is unreliable indicator of blood sugar response and much more. I know that the only solution is to use your blood glucose meter and your test strips to determine how you react to each food and type of food.

What surprises me the most is why it took so long to make this known. Consider that the glycemic numbers were developed using healthy people and not people with diabetes. For years many of us with diabetes have been saying that we have found the glycemic numbers have not matched what our meters tell us and are often even well outside the 15 percent possible error for the test strips we use.

The glycemic index of a given food, a value that aims to quantify how fast blood sugar rises after eating it, can vary by an average of 20 percent within an individual and 25 percent among individuals, report scientists from the Jean Mayer USDA Human Nutrition Research Center on Aging (USDA HRNCA) at Tufts University.

The study, published in the American Journal of Clinical Nutrition on Sept. 7, suggests glycemic index has limited utility as a tool to predict how a food affects blood sugar levels.

Developed as a way to help diabetic individuals control their blood sugar, glycemic index is intended to represent the inherent effect a food has on blood sugar levels. However, the glycemic index is becoming used for broader purposes such as food labeling, and has served as the basis for several popular diets.

"Reports frequently tout the benefits of choosing foods with low glycemic index and glycemic load values. Our data suggest those values may not be reliable in terms of a daily intake. A better approach to choosing foods is to consume a diet primarily composed of vegetables, fruits, whole grains, nonfat and low-fat dairy products, fish, legumes (beans), lean meats with preference to preparing food with liquid vegetable oils, and equally as important, to choose healthy foods and beverages you really enjoy," said senior study author Alice H. Lichtenstein, D.Sc., senior scientist and director of the Cardiovascular Nutrition Laboratory at the USDA HNRCA. Lichtenstein is also the Gershoff Professor at the Friedman School of Nutrition Science and Policy at Tufts.

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 10 individuals used by typical glycemic index methodology, as did the six feeding challenges and five-hour blood glucose measuring window.

The team also tested for the influence of biological characteristics: sex, body-mass index, blood pressure, physical activity, and several others. Most factors had only a minor statistical effect on glycemic index variability. Blood insulin response as measured by insulin index and HbA1c, a measure of longer term glucose control, had the largest effect, accounting for 15 and 16 percent of the variability, respectively.