Glycemic index shouldn't concern people without diabetes

(Reuters Health) – People without diabetes don’t need to worry about where a food falls on the glycemic index – even if they’re overweight or obese, according to a new study.

Despite having roughly the same amount of available carbohydrates, some foods increase people’s blood sugar more than others. Foods that cause blood sugar levels to rise sharply over two hours are said to have a high glycemic index. Foods that don’t cause a big rise in blood sugar have a low glycemic index.

“The big question is, does that translate to any health issues,” said Dr. Frank Sacks, the study’s lead author from Brigham and Women’s Hospital and Harvard Medical School in Boston.

The researchers write in JAMA that some nutrition policies encourage eating food low on the glycemic index. There has also been some advocacy to put the glycemic index value of foods on packaging.

It’s uncertain whether people benefit from a low-glycemic diet - especially if the diet is generally heart-healthy and nutritious, the researchers add.

For the new study, they arranged for 163 overweight adults to each follow four heart-healthy diets for five weeks at a time between April 2008 and December 2010. The participants completed at least two diets.

One diet included high carbohydrate foods that are high on the glycemic index. A second diet included high-carbohydrate, low-glycemic food. A third included low-carbohydrate, high-glycemic food. The final include low-carbohydrate, low-glycemic food.

The difference between the diets could be small, because fruits and grains may be healthy, but fall in different parts of the glycemic index.

“A higher glycemic diet would have more bananas and instant oatmeal,” said Sacks. “A lower glycemic index would have more dried apricots and steel cut oats.”

The participants were provided with all their meals, snacks and calorie-containing drinks to complete the diets.

Overall, the researchers generally found no improvement in key markers of health between low- and high-glycemic diets.

There was no improvement in reactions to the hormone insulin, which allows the body to turn sugar - or glucose - in the blood into energy. There was no improvement in the amount of fat in people’s blood. There was also no improvement in systolic blood pressure, which is the top number of a reading that measures pressure during a heartbeat.

Sacks said it’s likely that people’s bodies can handle variations in food on the glycemic index – even if they are overweight and are already having problems with insulin resistance.

“I guess it just works normally in most people,” he said, adding that glycemic index should be studied among people with type 2 diabetes, which is also commonly known as adult-onset diabetes.

He said existing studies suggest there may be a benefit for people with diabetes, but there needs to be more research.

Dr. Robert Eckel, who wrote an editorial accompanying the new study, said the study’s message is that the glycemic index is not that important if a diet is already heart healthy.

“If you’re eating a heart-healthy diet, glycemic index is not important to consider,” said Eckel, a past president of the American Heart Association and a professor at the University of Colorado Anschutz Medical Campus in Aurora.

“I think the emphasis need to be on the overall diet pattern,” he said.

Sacks said people who want a good overall diet should look toward Mediterranean-style diets or the Dietary Approaches to Stop Hypertension (DASH) diet, which emphasizes vegetables, fruits, fat-free dairy, whole grains, fish, poultry, nuts and vegetable oils.

SOURCE: JAMA, online December 12, 2014.