Sunday, December 21, 2014

Is glycemic index of foods becoming irrelevant? Some think so!

Ever since the Glycemic Index (GI) and Glycemic Load (GL) concepts became acceptable for differentiating carbohydrates in terms of their ability to release glucose into the blood and the pace at which blood glucose spikes after food consumption, no serious challenge was made against it. Now comes a report originating from the reputed National Institute of Health at Bethesda, USA (NIH) indicating that for a normal person GI and GL do not make much difference in spawning heart disease, blood pressure and diabetes. According to this new findings, high GI foods do not cause these diseases and on the contrary low GI foods can increase insulin insensitivity which is not desirable. Original GI innovators who pioneered the study in 1988 ultimately coming out with the GI yardstick, do not seem to be agreeing to the conclusion of the latest NIH study and here is this issue discussed threadbare.

The idea that all carbohydrates are not created equal has become the foundation of many popular diets. Some argue that foods like white bread and potatoes, which have a high so-called glycemic index because they spike blood sugar and insulin, should be avoided in favour of  healthful carbs like whole grains and non-starchy vegetables. But rigorous new research from the National Institutes of Health suggests that for people who already follow a healthful diet, the glycemic index (GI) may not be very important. The study found that diets containing low glycemic foods did not lower cholesterol compared to diets containing mostly high glycemic foods. Nutrition experts argue that low glycemic diets improve blood sugar levels and insulin sensitivity. But the new study found that low glycemic diets actually made insulin sensitivity worse. "The dogma out there is that a high glycemic index is bad," said Dr Robert Eckel, a past president of the American Heart Association, who was not involved in the research. "I hope that ultimately the glycemic index will be left on the shelf." Developed in 1981, the glycemic index reflects the extent to which carbohydrate-containing foods raise a person's blood sugar and subsequent need for insulin. The idea is that low glycemic foods are better for health, warding off diabetes and weight gain, because the carbs they contain are digested at a slower rate. The glycemic index indicates how quickly a particular carbohydrate raises blood sugar, but not how much of it is in a typical serving of a given food. So proponents of the index have also come up with another system, known as glycemic load, which takes portion sizes into account. Last year, a committee of scientists led by the chair of the Harvard School of Public Health called for glycemic values to be included on food labels and emphasised in dietary guidelines. The committee said it was crucial that the public understand the glycemic response to foods "given the rapid rise in diabetes and obesity." In the new study, researchers wanted to find out whether diets that were similar in calories and carbohydrates but composed of either high or low glycemic foods had different effects on cardiovascular health. So they recruited 163 people who were mostly overweight and had high blood pressure, putting them at greater risk of heart disease and Type 2 diabetes. The subjects were rotated through four diets for five weeks at a time, with all of their food provided to them. The researchers said they devised each diet to be heart healthy, with plenty of fruit, vegetables, beans, fish, poultry, lean meat and grains. Two of the diets were slightly higher in carbs than what an average American eats, and two were slightly lower. Researchers then altered the types of carbs they contained. The low glycemic diets included things like whole grain bread and cereal, apples, steel-cut oats, and non-starchy vegetables. The high glycemic diets allowed things like white bread, carrot and bran muffins, instant rice and instant oatmeal, and sweet snacks like honey, bananas, and apricots in heavy syrup. When the overall amount of carb intake was lowered, cardiovascular risk factors like cholesterol, triglycerides and blood pressure moved in the right direction. But when two diets had similar amounts of carbs and calories, the low glycemic approach did not improve insulin sensitivity, cholesterol or blood pressure levels. Unnecessary fuss over GI Dr Frank M Sacks, the lead author of the study and a professor at Harvard Medical School and Brigham and Women's Hospital, said that other trials carried out even longer had reached similar results. He said that people should eat whole grains, fresh produce and high fibre foods because of the nutrients they contain. But unless someone has diabetes and must monitor their blood sugar levels, people who are already following a health-ful diet do not need to worry about the blood-sugar impact of one type of fruit or grain versus another. "The takeaway is a good message for people," he said. "They can pick foods that are part of a healthy dietary pattern without wondering if they're high or low glycemic. They don't have to learn that system." The developer of the glycemic index, Dr David Jenkins, a professor of nutrition at the University of Toronto, added that the study was limited because it did not include people with Type 2 diabetes, a rapidly growing population that has the most problems with blood sugar control. "If they had done that," he said, "they would have made it easier to see some of the cardiovascular benefits."
It may be recalled that there have been demands from some section of the nutritionists about the urgent need to declare GI of each food on the label as they feel that provides an option to the consumer to select low GI foods. But if the latest study is confirmed and there is unanimity among the peers regarding the limited role GI plays in life style diseases for a normally healthy person, including GI values may have opposite effect viz such foods' potential to worsen insulin insensitivity. The rider contained in the study in NIH that their findings apply only to those consuming a "healthy" diet regularly makes it again controversial because most Americans do not have the habit of eating such foods containing predominantly whole food grains, fruits and vegetables. If this is so are they not better of sticking to low GI foods? Of course ideal thing would be to change the diet to include more and more high fiber foods derived from unrefined grains and fruits and vegetables. GI and GL definitely will play a role in the lives of people affected by Type II diabetes as it is essential for them to prevent glucose spikes for which low GI foods are a better bet.


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