QUESTION: I keep hearing about this thing called glycaemic index. What is it, really?
Answer: I know it sounds as complicated as a math problem, but glycaemic index (GI) is really easy to understand. Foods containing carbohydrates affect our blood sugars. Remember, carbohydrates are broken down into glucose. This glucose floats around in our bloodstream until insulin tells our cells to pick it up. Then the glucose leaves our bloodstream and goes into our cells so the cells can use it for energy.
Different foods contain different amounts and different types of carbohydrates. The three basic types of carbohydrates are sugars, starches, and fibre.
•Sugars can be further broken down into sucrose (the sugar we use to sweeten our drinks), fructose (the sugar found in fruits) and lactose (the sugar found in dairy products). These sugars are in the most basic form and are easily absorbed by the body.
• Starches are complex carbohydrates. That means they are a network of simple sugars strung together. These are more difficult for the body to absorb because the body has to first break them down into simple sugars before they can be absorbed. Starches are found in foods such as bread, cereal, pasta, potatoes, and corn.
• Fibre is also a complex carbohydrate. However, it cannot be broken down by the body. Hence, it cannot be absorbed and it just passes straight through the digestive system and out of the body. Fibre is found in foods from plant sources such as fruits, vegetables, beans, seeds, and nuts.
Now that we have established the three different types of carbohydrates, it is easy to see that they will affect our blood sugar differently. Fibre will not affect our blood sugar because it cannot be absorbed by the body. Starches will be absorbed more slowly because they have to go through a breakdown process. But sugars will be absorbed rather quickly, and will lead to rapid spikes in our blood sugar.
The glycaemic index simply shows how quickly a carbohydrate food affects our blood sugar when eaten on its own. The measure ranks food on a scale of zero to 100. A low GI food is one that won’t raise your blood sugar rapidly, whereas a high GI food will cause rapid spikes in your blood sugar. The GI values can be broken down into three ranges.
Low GI: 55 or less
Medium GI: 56 to 69
High GI: 70 to 100.
The glycaemic index of a food is determined by giving people a serving of the food that contains 50 grams of carbohydrate minus the fibre, then measuring the effect on their blood glucose levels over the next two hours. Of course, our meals are not made up of single foods, and the combination of foods in our meals affects how the carbohydrates are absorbed. Hence, it is difficult to use the glycaemic index only to guide our food selection, but it is useful to know that a bottle of soda will cause a rapid spike in our blood sugar while a handful of raw peanuts will be absorbed more slowly.
Foods with a high glycaemic index are quickly digested and absorbed, causing a rapid rise in blood sugar. These foods that rank high on the GI scale are often high in processed carbohydrates and sugars. For example, one slice of white bread has a glycaemic index of 72. You definitely want to limit white bread in your diet. However, some healthy foods have high glycaemic indices too. Watermelon can have a glycaemic index of 80! Does that mean you should not eat watermelon? Of course not. There are many other benefits to watermelon; you just have to eat it in moderation.
On the other hand, foods with a low GI are digested and absorbed at a slower rate, and subsequently, cause a slower rise in blood sugar levels. These are typically rich in fibre, protein and/or fat. Examples of these include apples with a glycaemic index of 28, raw carrots at 16, and peanuts at seven.
In conclusion, you don’t need to be a nutritionist or dietician to spot low GI foods. If you choose whole grains, fruits, vegetables, and legumes, you’ll more than likely be eating a low GI diet, as opposed to eating mostly processed foods, which tend to be high GI. Remember, glycaemic index is only a measure used in carbohydrate foods, so it does not relate to proteins or fats. I challenge you to drop some high GI foods this week and focus on low GI foods that will not affect your blood sugar as much.
Novia Jerry Stewart, MSc, RPh, is a pharmacist who specialises in diabetes care. She may be contacted for diabetes care coaching sessions at firstname.lastname@example.org.