One diet tool I get a lot of questions about is the glycemic index (GI).
For those of you who are unfamiliar with the term, GI measures how a carbohydrate food acts in your bloodstream.
Absorption rates of carbohydrates are compared to pure sugar and ranked on a scale of 100. The thinking is that foods with a lower GI are absorbed more slowly and are healthier because they don’t “spike” blood sugars.
If you were comparing GI to fuel in a fire, low GI foods are like logs (slow-burning) and high GI foods are like kindling (light up quickly, but don’t last).
Unfortunately, many factors influence the GI index, making it a confusing diet tool. Some of these include:
Cooking method: the longer you cook something, the higher its GI. For example, al dente pasta would have a lower GI than pasta cooked soft.
Acidity: acids slow digestion, so acidic fruit has a lower GI than low-acid fruit.
Fat: fat makes the stomach empty more slowly; consequently, a Snickers bar has a lower GI than most fruit.
Soluble fibre: fibre increases digestion time, thereby lowering its GI.
Type of starch molecules: some starch molecules are more branched than others (therefore harder to break down)- sweet potatoes have a lower GI than white potatoes.
Processing: highly processed foods tend to have a higher GI.
Furthermore, the GI diet does not take into account that most of us eat mixed meals, not individual food items.
We don’t eat a plain, baked potato without anything else for supper. We add butter, sour cream and maybe a steak. These would all lower its GI and slow absorption of sugar, but do not necessarily make the meal healthier.
If using the GI diet, also keep in mind that your blood sugar is not only affected by the type of carbohydrate, but by the amount (glycemic load).
For example, two cups of brown rice will raise your blood sugars more than one cup of white rice. Finally, realize that GI does not speak to the amount of vitamins and minerals in a food, and that many high GI foods are still healthy.
- Serena Caner is a registered dietician who works at Shuswap Lake General Hospital.