Glycemic Index 101
This carb-ranking scale can help better your blood-glucose levels

Lisa Goldman

There’s dietary regimen out there that reduces the risk of disease and helps control LDL (“bad”) cholesterol. It doesn’t involve counting calories, cutting out carbs or drinking weird shakes. It’s called the GI diet but it has nothing to do with the U.S. military. It’s the 27-year-old food-and-drink plan known as the glycemic index, and it can reduce your risk of type 2 diabetes, heart disease and certain cancers. Properly followed, it can help control blood pressure and blood glucose and even boost energy. If that’s not incentive enough for you to give it a go, it can also curb your appetite by making you feel full longer and promote weight loss and maintenance.

Photo by Chad Johnston/Masterfile

What is it?

In the early 1980s, Dr. David Jenkins, a University of Toronto nutritional science professor and director of the Clinical Nutrition and Risk Factor Modification Centre at St. Michael’s Hospital, devised the GI, a scale that shows how different carbohydrate foods affect our blood-sugar levels. He and his colleagues studied how the body digests carbohydrates by recording subjects’ blood-sugar levels after ingesting different foods. “We knew that carbohydrates were not the only factor that determined the blood-glucose response,” says Jenkins. “So when we started our work, everyone was interested in fibre, which can make a positive difference to the blood-glucose response, but we also wanted to look at how different carbohydrates affected it,” he says.

Interesting results emerged. “Our studies showed that pasta triggered half the blood-glucose response of white bread. That came as a surprise. Why should white pasta produce a different response than white bread? We also found that beans, peas and lentils produced a lower response than white bread, even though they have about the same amount of carbohydrates,” says Jenkins. This proved that the amount of carbs in two foods may be the same, but their impact on blood-sugar levels can be entirely different.

Enter the glycemic index.

The GI ranks carbohydrate-rich foods from zero to 100 (100 = pure glucose), according to how much and how quickly they raise blood-glucose levels after eating. Hundreds of foods are currently ranked in the GI. Items that have a high-GI rating of 70 or more (e.g., white bread, mashed potatoes, french fries and most dry cereals) are quickly digested and make blood-glucose and insulin levels spike. That can be bad for your health. A steady diet of high-GI foods can overwork the pancreas, the organ that must produce the insulin we need to store blood sugar from food as energy for later use.

Low-GI foods — such as barley, pasta, parboiled rice and whole wheat and pumpernickel bread — are digested and absorbed more slowly, producing gradual rises in blood sugar. These foods are easier on the metabolic system because they trigger a slower release of insulin from the pancreas. High levels of insulin triggered by high-GI foods cause fat to be deposited and stored in the body instead of being burned as energy. In a worst-case scenario, too much stimulation of insulin and fat storage can exhaust the pancreas and lead to type 2 diabetes.

Medium-GI foods are ranked 56 to 69 (e.g., popcorn, bananas, rye bread and brown rice). We should choose carbs from the medium and low brackets more often.

Who needs it?

Pretty well everyone can benefit. “The only people who don’t need the diet are those with a healthy body weight, people who exercise frequently, sleep well and aren’t under much stress,” says Jenkins. “And there aren’t many people in this category.”

Anyone can follow the GI. It’s especially good for people who have diabetes and high levels of blood cholesterol, blood pressure and blood sugar. It’s also good for people whose fat tends to accumulate around the belly. If all those reasons aren’t enough, the GI diet boasts other good-for-you features. “Low-GI foods are also often lower in fat, higher in fibre and high in nutrients and antioxidants,” says Fredericton-based registered dietitian Ainsley Archer.

How to use it

While there are no set rules as to how many low- and high-GI foods you’re allowed to consume at every meal, always try to choose at least one medium- or low-GI food when you sit down for breakfast, lunch and dinner. If you’re having a bowl of Rice Krispies (GI = 82), for example, cut up some strawberries (GI = 40) or sprinkle a few almonds (GI = 0) on top. Have a low-fat, sugar-free yogourt (GI = 15) with your lunchtime bagel (GI = 72). The lower-GI item can slow the absorption of its high-GI counterpart. Other ways to march to the GI drum:

• Enjoy lots of fruit, veggies and lower-fat milk products. “Temperate-climate fruit such as apples and pears are famous for having low GIs,” says Jenkins.

• Limit processed and refined starchy foods, opting instead for whole grains such as barley, brown rice, cornmeal and oatmeal. Eat pumpernickel, oat-bran and whole wheat breads rather than white.

• Choose sweet potatoes or boiled white potatoes instead of mashed white spuds, especially instant.

• “Add low-GI beans and lentils to soups, stews, pasta sauces, chilis and salads,” says Archer.

• Use homemade vinaigrettes on salads instead of sugary commercial dressings.

• But a food’s GI is not the only consideration. Limit intake of pasta, which has a low GI but is nevertheless high in carbohydrates. “Pastas are wonderful as long as you don’t consume too much,” says Jenkins.

• Be wary of foods that have a low GI, but are high in calories and fat: M&Ms have a GI of 32, low-fat ice cream of 50 and potato chips of 54. Alternatively, some foods have a high GI but are low in calories and fat and should be included in your diet (watermelon = 72, rice cakes = 82, baked potato = 85).

For more on the GI, go to www.glycemicindex.com.

THE GI SOLUTION

Choose low-GI foods more often and pair high-GI items with lower ones

Low-GI foods (55 and under)

Asparagus, broccoli, cauliflower, cucumber, eggplant, green beans, lettuce, peanuts, peppers, snow peas, spinach, tomatoes, zucchini

Medium-GI foods (56 to 69)

High-GI foods (70 and over )

Glycemic load

The glycemic load (GL) is a measure of the digestion speed of various carbohydrates. It is calculated by multiplying a food’s GI by the amount of carbs in a single serving, then dividing by 100. A GL of 20 or more is high, 11 to 19 is medium and 10 and under is low. For instance, watermelon has a high-GI rating (72), but its GL is low (8) because the number of grams of available carbs (11) in a single serving (one cup, 250 mL) is small owing to its high water content. Another example: one teaspoon (15 mL) of jam has a GI of 51. Its GL is only 2.5 (51 x 5 grams of carbohydrates) divided by 100 = 2.5).

Photo by Chad Johnston/Masterfile