Now glycemic index is a worldwide popular index for measuring blood glucose level specially people who are suffering diabetes. The glycemic index (GI) is a number associated with a particular type of food that indicates the food's effect on a person's blood glucose(also called blood sugar) level. A value of 100 represents the standard, an equivalent amount of pure glucose.
The GI represents the total rise in a person's blood sugar level following consumption of the food; it may or may not represent the rapidity of the rise in blood sugar. The steepness of the rise can be influenced by a number of other factors, such as the quantity of fat eaten with the food. The GI is useful for understanding how the body breaks down carbohydrates and only takes into account the available carbohydrate (total carbohydrate minus fiber) in a food. Although the food may contain fats and other components that contribute to the total rise in blood sugar, these effects are not reflected in the GI.
Now researchers have found that it does not work always in the right way.Individual response to glycemic index values vary so much that it may not be useful in indicating blood sugar response, says research published in the “American Journal of Clinical Nutrition”.
The glycemic index (GI) of a food indicates the speed with which blood sugar can be expected to rise after a person eats it. Each food gets a score out of 100 on the index, for example, 40 for baked beans.
Glycemic load is a measure that applies the GI to a portion of food. The glycemic load for a 150-gram serving of baked beans would be 6.
GI is used to help people with diabetes to control their blood sugar. Some food labels carry GI measurements. More recently, a number of popular diets have been based on GI. Lists are available for people to check the GI and glycemic load of different foods.
However,its usefulness is controversial, because individual responses to a particular food can vary.
Scientists from the Jean Mayer United States Department of Agriculture (USDA) Human Nutrition Research Center on Aging (HRNCA) at Tufts University have questioned are GI a valid measure, after randomized, controlled? But repeated tests on 63 healthy adults suggested otherwise.
The GI does not work on white bread
The volunteers participated in six testing sessions over 12 weeks. They fasted and abstained from exercise and alcohol before each session.
Throughout the session, they ate either white bread or a glucose drink, in random order.The bread was the test food, and the drink was a reference control. The fast facts about GI values are :
- Plain white baguette scores 95 on the glycemic index
- White wheat flour bread scores 75
- An average apple scores 36
- Hummus, a chick-pea dip, scores 6
Each item contained 50 grams of available carbohydrate.
Blood glucose levels were measured several times over the next 5 hours, and GI was calculated using standard methods.
The result put the average GI value of white bread at 62, making it a"medium" GI food, but scores varied by 15 points in either direction.
Among the 22 participants, the blood sugar response was low, in 23 it was medium, and in 18, it was high. This range effectively put white bread in all three GI categories. Moreover, individual responses varied by up to 60 points between tests.
And this could be partly due to insulin index and baseline HbA1c levels. These readings reflect long-term glucose control.
In this research, these factors showed the highest range in measures, around 15percent to 16 percent difference. This suggests that an individual's metabolic response to food impacts their GI values.
Asa result, the scientists have questioned how useful the GI is for predicting a food's impact on blood sugar levels.
The role of GI in clinical and public health
Researchers used a higher number of participants, more tests and a longer measuring window than most GI tests do.
The team also observed at how the biological factors such as sex, body-mass index (BMI),blood pressure, and physical activity impact GI variability. In most cases, the impact was minor.
The leader of the researcher point out that the results do not mean that food with a high GI is really healthy or that one with a low GI is unhealthy, but it does imply that the usefulness of these measures for managing clinical and public health may be limited.
GI measures cannot tell us which foods are healthy?
Lead author Nirupa Matthan points out that a person consuming the same amount of the same food three times should have a similar blood glucose response every time,but this did not happen.
For this, she suggests that GI values are "unlikely to be useful in guiding food choices."
"A food that is low glycemic index for you one time you eat it could be high the next time, and it may have no impact on blood sugar for me," she adds.
"Based on our results, we feel strongly that glycemic index is impractical for use in food labeling or in dietary guidelines at the individual level. 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." says Nirupa Matthan.
Senior study author Alice H. Lichtenstein notes that people are often encouraged to choose foods with low GI values.
Alternatively, she suggests following 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."
So the researcher now calls for experts to rethink the link between GI estimates and chronic disease risk.