A new study finds that the glycemic index just can't be trusted. The study, done by researchers at Tufts University, found that an individual's blood sugar response to foods, which the glycemic index measures, varies widely.

What that means is your response to white rice can be totally different than mine.

Researchers found the glycemic index, a value that aims to quantify how fast blood sugar rises after eating a given food, can vary by an average of 20 percent within an individual and 25 percent among individuals. The research was conducted by scientists from the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts and results were published in the American Journal of Clinical Nutrition.

Their bottom line: "The much-touted glycemic index has limited utility as a tool to predict how a food affects blood sugar levels," according to Tufts own Healthy & Nutrition Letter.

"Glycemic index values appear to be an unreliable indicator even under highly standardized conditions and are unlikely to be useful in guiding food choices," said lead study author Nirupa Matthan, scientist in the Tufts Cardiovascular Nutrition laboratory. "If someone easts the same amount of the same food three times, their blood glucose response should be similar each time, but that was not observed in our study. 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 your blood sugar."

The glycemic index was originally developed as a way to help diabetic individuals control their blood sugar. Recently it has been used in food labeling and has served as the basis for several popular diets.

Matthan and colleagues recruited 63 volunteers, who underwent six testing sessions over 12 weeks. Volunteers fasted and abstained from exercise and alcohol before each session. Then they consumed either white bread or a glucose drink in random order. Each option contained 50 grams fo carbohydrate. Blood glucose levels were measured at multiple time points for five hours after eating and glycemic index was calculated.

The average glycemic index value of white bread was 62, placing it in the medium category. But deviations averaged 15 points in either direction, effectively placing white bread in all three glycemic index categories. It was considered a low glycemic index food for 22 volunteers; medium for 23 and high for 18 volunteers. Even for the same individuals, glycemic index values could differ by more than 60 points between trials.

"Reports frequently tout the benefits of choosing foods with low glycemic index and glycemic load values," said Alice Lichenstein, director of the laboratory. "Our data suggest those values may not be reliable in terms of a daily intake."

A better approach is one we probably already know — consume a diet primarily composed of vegetables, fruits, whole grains, nonfat and low-fat dairy products, fish, legums and lean meats.

Q and A

Q: Is it true that caffeine interferes with calcium absorption?

A: Not enough to worry about, according to the University of Berkeley Wellness Letter. Caffeine can slightly reduce calcium absorption, but this is significant only if you aren't consuming adequate calcium. A few studies have linked caffeinated beverages to reduced bone density and increased fractures, but the effect is seen almost exclusively in people with low calcium intake. In any case, the negative effect of caffeine is small enough to be fully offset by one to two tablespoons of milk, according to Dr. Robert Heaney, a noted expert on calcium and osteoporosis at Creighton University in Omaha. Rather than worry about calcium-caffeine interactions, just be sure to get enough calcium from food, preferably, and supplements. The recommended dietary allowance is 1,200 mg a day for women over 50 and men over 70 and 1,000 mg for other adults. In addition, consume enough vitamin D, which works with calcium. The recommended amount for vitamin D is 800 to 1,000 IU a day for most people. — University of Berkeley Wellness Letter.

RECIPE

I often shy away from potato soup because of the calories, but Cooking Light magazine has a lightened-up version, Quick Loaded Potato Soup, that is just as tasty as a full fat version.

Quick Loaded Potato Soup

2 pounds russet potatoes, peeled and cubed

1/4 cup all-purpose flour

2 cups 2 percent reduced-fat milk

1 cup unsalted chicken stock

3/4 cup light sour cream

1 1/4 teaspoons kosher salt

1/2 teaspoon black pepper

2/3 cup sharp Cheddar cheese, shredded

6 center-cut bacon slices, cooked and crumbled

3 tablespoons chopped fresh chives

Place potatoes in a Dutch oven; add cool water to cover by 2 inches. Bring to a boil over high heat; reduce heat to medium and simmer until tender, 11 to 14 minutes. Remove from heat; drain. Return potatoes to pan; mash with a potato masher to desired consistency. Measure flour and whisk together with milk and stock in a medium bowl. Stir milk mixture into potatoes; cook over medium, stirring often, until thickened and bubbly, about 4 minutes. Remove from heat; stir in sour cream, salt and pepper. Ladle soup into 6 bowls; top with cheese, bacon and chives.

Serves 6 (serving size about 1 1/4 cups soup, about 1 1/2 tablespoon cheese, 1 crumbled bacon slice and 1 1/2 teaspoon chives).

Per serving: 290 calories, 12 g protein, 37 g carbohydrate, 10.4 g fat, 34 mg cholesterol, 2 g fiber, 657 mg sodium.

Charlyn Fargo is a redistered dietitian with Hy-Vee in Springfield, Ill., and a spokesperson for the Illinois Academy of Nutrition and Dietetics. For comments or questions, contact her at [email protected] or follow her on Twitter @NutritionRD. To find out more about Charlyn Fargo and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.