Confusion about carbohydrates is common. Carbs are important because they give your body energy. Certain kinds of carbs can quickly raise your blood sugar levels. Other carbs are digested slowly and raise the blood sugar level gradually. Now, which kind would you rather eat? While the answer is not completely clear-cut, you can use the glycemic index as a tool to help you choose carbs carefully.

The glycemic index (GI) measures how carbohydrate-rich foods affect our blood sugar. Foods are ranked on a 0 to 100 scale based on how quickly they raise blood glucose levels compared to a reference or standard food (usually white bread or glucose). That's how quickly our bodies break down carbs into sugar for energy. The overall effect of a particular food's GI and the amount of carbs in the food is called the glycemic load (GL).

Foods high on the GI are broken down rapidly and can quickly raise blood sugar levels. Low-GI foods are digested slower and raise blood sugar levels more gradually. By controlling and delaying hunger, low-GI diets have also been shown to make weight loss easier. In fact, even moderate reductions in a person's overall glycemic load can speed up body fat loss in overweight or obese adults.

One study compared the impact of 4 low-fat, high-fibre diets on an overweight or obese person's health. The difference between each diet was the quality and quantity of the carbs that test subjects ate. All 4 diets resulted in weight loss for the overweight or obese test subjects, but the diet that featured high carbs and low-GI foods saw the best overall results, lowering LDL (bad) cholesterol and trimming body fat mass.

The Human Nutrition Unit at the University of Sydney in Australia is "home" of the glycemic index, conducting ongoing research and maintaining a database of foods and their GI rankings. Their advice is not to worry too much about the numbers game and simply focus on choosing the best foods and eating a variety of healthy foods. A few things to think about:

  • Select fresh foods. In general, the more cooked and processed foods are usually higher on the GI, but this is not always the case.
  • The GI rule of thumb: choose slow carbs, and not necessarily always low carbs. Carbs can be healthy additions to your diet (for example, they provide fibre), so you shouldn't eliminate all of them. Instead, opt for carbs that are lower on the GI.
  • Lots of foods, including meats, tofu, eggs, avocados, and some alcoholic beverages have little or no carbs. Thus, they don't have a GI.
  • Pasta is special. Thanks to its unique, starchy structure, the carbs in pasta are less able to break down rapidly. Pasta should be cooked al dente or just a bit firm. Overcooked pasta gets a GI boost. Adding acidic ingredients like vinaigrette to a meal can reduce its GI level, and starchy high-GI potatoes can be made healthier by serving them cold, as in a refrigerated potato salad tossed with vinaigrette.

Here are some sample GI levels of some common foods:

Low GI (55 or less) Oat bran bread, al dente pasta, chick peas, lentils, kidney beans
Medium GI (56-69) New potatoes, oatmeal, popcorn, brown rice, basmati rice, whole wheat bread
High GI (70 or higher) Instant mashed potatoes, baked white potato, short-grain rice, corn flakes, white bagels, soda crackers, French fries