The glycemic index measures how carbohydrates in food affect blood glucose (sugar) levels in the first two hours after consumption. It was first measured in a group of ordinary people, and provides a good idea of how the body responds to a standard amount of a given food. Different foods contain differing amounts of available carbohydrate – those the body can digest and use. For instance, although fibre is carbohydrate the body cannot digest it.
In the index, equal amounts of available carbohydrate from different foods are compared to one another. As an example, one cup (250 mL) of oatmeal has 21 grams of available carbohydrate and a glycemic index of 42. It has half the effect on blood glucose as a cup of Rice Krispies™, which has the same amount of available carbohydrate, but a glycemic index of 84. The higher the glycemic index number, the higher blood glucose rises after eating the food.
The amount of food eaten also plays a role. Eating pasta increases blood glucose for many people, even though it has a relatively low glycemic index. Usually, this is because they are eating far more pasta than recommended in one serving. A standard serving of pasta at a meal is about one cup of cooked pasta. Amazingly, the average restaurant serving of pasta has risen to over three cups in the past 30 years!
In research studies, the concept of glycemic load has been used to account for varying serving sizes among different people. Glycemic load considers the glycemic index along with the amount of available carbohydrate.
This is just a fancy way of saying that eating too much of any food is not good for you! Even a food with a low glycemic index makes blood glucose rise if too much is eaten. The reverse is also true. A small amount of high glycemic index food will not make blood glucose climb. Many people can add half a teaspoon (2 mL) of table sugar to a cup of tea without it having any visible effect on blood glucose.
Many lists of glycemic index and glycemic load numbers are available on the Internet and elsewhere. However, focusing only on numbers can be frustrating. You may find the following simple guidelines more useful in lowering the glycemic index and glycemic load of your diet.
Dividing your plate to contain half vegetables, a quarter protein, and a quarter of starchy foods will help limit the total amount of carbohydrate you eat during a meal.
Acidic foods help to lower the glycemic index of a meal. Use vinaigrette or oil-and-vinegar mixtures on salads at meals.
Enjoy all types of vegetables. However, eat potatoes in moderation as they have a high glycemic index.
Try to eat foods as close to their whole, natural state as possible. The more processed a grain product is, the higher the glycemic index will be. Less processed grain products are also higher in nutrients and fibre. For instance, choose cereals primarily made of oats, barley or bran. Use whole-grain breads or those made with stone-ground flour.
Include low-fat milk or yogurt. These foods have a very low glycemic index and will lower the overall glycemic index of your meals.
Include plenty of fruit in your diet, and get a variety of different fruits. As a group, fruit has a very low glycemic index. Dates and melons are among the exceptions - remember not to eat too many.
The glycemic index and glycemic load are only two factors to consider when deciding what to eat. Others are just as important. Eat a variety of foods from all the food groups (grains, fruits and vegetables, milk, and meat and alternatives). Limit high-fat foods, and try to use healthier types like canola, olive, or peanut oil. Spread out your food intake by not eating too much at any one time.