What is the difference between glycemic index (GI) and glycemic load (GL)?
Your blood glucose rises and falls when you eat a meal containing carbs. How high it rises and how long it remains high depends on the quality of the carbs (the GI) and the quantity. Glycemic load or GL combines both the quality and quantity of carbohydrate in one ‘number’. It’s the best way to predict blood glucose values of different types and amounts of food. The formula is:
GL = (GI x the amount of carbohydrate) divided by 100.
Let’s take a single apple as an example. It has a GI of 40 and it contains 15 grams of carbohydrate.
GL = 40 x 15/100 = 6 g
What about a small baked potato? Its GI is 80 and it contains 15 g of carbohydrate.
GL = 80 x 15/100 = 12 g
So we can predict that our potato will have twice the metabolic effect of an apple. You can think of GL as the amount of carbohydrate in a food ‘adjusted’ for its glycemic potency.
Although the GL concept has been useful in scientific research, it’s the GI that’s proven most helpful to people with diabetes. That’s because a diet with a low GL, unfortunately, can be a ‘mixed bag’, full of healthy low GI carbs in some cases, but low in carbs and full of the wrong sorts of fats such as meat and butter in others. If you choose healthy low GI foods—at least one at each meal—chances are you’ve eating a diet that not only keeps blood glucose ‘on an even keel’, but contains balanced amounts of carbohydrates, fats and proteins.
We suggest that you think of the GI as a tool allowing you to choose one food over another in the same food group—the best bread to choose, the best cereal etc.—and don’t get bogged down with figures. A low GI diet is about eating a wide variety of healthy foods that fuel our bodies best—on the whole these are the less processed and wholesome foods that will provide you with carbs in a slow release form. So what’s the take-home message?
- Choose slow carbs, not low carbs
- Use the GI to identify your best carbohydrate choices.
- Take care with portion size with carb-rich foods such as rice or pasta or noodles to limit the overall GL of your diet.