What is the Glycemic Index?

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The Glycemic Index (or GI) represents one of the most significant medical breakthroughs with implications for weight management, disease management and general wellbeing. Before the discovery of the Glycemic Index, we were led to believe that all simple carbohydrates, like fruits and sugars broke down quickly in the body, and that complex carbohydrates, like breads and potatoes, broke down more slowly. We were therefore advised, that for health and energy, we should be eating more complex carbohydrates and in fact, that we should be making these the basis if our diets. The food guide pyramid, developed by the United States Department of Agriculture in 1992, suggests that we should be eating six to eleven servings of complex carbohydrates per day for health. The problem is, this very same starchy diet advocated for health, has been shown to be a major contributor to obesity, diabetes and other modern day diseases of lifestyle. Then came Dr. Atkins, who went against the grain by advocating his low carbohydrate, high protein diet for weight loss and so the pendulum swung from one side to another. What we know now, is that we can take both rather extreme dietary theories and create a new way of eating that is more balanced, more moderate and all together more healthy. Enter the world of GI diets.

What is the Glycemic Index?

The GI is simply a ranking of foods based on their immediate effect on blood glucose levels. It is a physiological measure of how fast, and to what extent, a carbohydrate food affects blood glucose levels. The GI can only be applied to foods that contain carbohydrate. Meats and oils, which are carbohydrate free, do not have a glycemic index.

After you eat a meal, all food (but particularly carbohydrate foods) gets broken down into a usable form of energy for the body called glucose. Protein foods, like meats are converted to amino acids and fatty foods, like oils are converted to fatty acids and glycerol. When these foods are eaten in excess though, the remainder will eventually get converted to glucose too. Glucose is the main energy source for our body and brain cells. Insulin is the hormone responsible for getting the glucose shuttled out of out blood and into our cells for use as energy. It is like the “key that unlocks” the door to our cells allowing energy to enter.

When the body gets a load of glucose, a subsequent rise in insulin levels follows; glucose gets taken into the cells and blood sugar drops. The faster blood sugar rises, the faster it falls, and the slower it rises, the slower it falls. Carbohydrates that breakdown quickly during digestion have the highest GI’s and are referred to as high GI. Carbohydrates that breakdown slowly, releasing glucose gradually into the blood stream, have low GI’s. Glycemic index scores are calculated relative to the GI of glucose, which is 100. High GI foods have a GI of greater than 55, and low GI foods are below 55 GI points. When we eat high GI foods, like white bread or cornflakes, our blood glucose levels rise higher and faster than they would with low GI foods, like wholegrain seed breads or wholewheat pasta. This means more insulin is secreted in response and blood sugar levels fall faster than they would with low GI foods. Eating low GI foods on the other hand will help prevent your blood sugar levels from spiking and result in a more sustained release of glucose energy.

Factors affecting the Glycemic Index

The GI is not always so clean cut and there are many factors affecting the GI if foods that need to be taken into consideration before planning your diet. These include:


Adding some acidity from vinegar or lemon juice to food helps decrease the GI of the meal. So if you must have that high GI baked potato, add some balsamic vinegar to help lower the GI.

Food preparation.

Slightly undercooked or raw foods have a lower GI than cooked or over cooked foods. So, lightly steamed vegetables will have a lower GI then vegetable soup for example.


Slightly under ripe fruit has a lower GI than overripe fruit, however, ripe fruit is more nutritious.

Protein and fat content.

The presence of protein or fat in a meal lowers the GI of that meal. For example a plain baked potato with a salad is a high GI meal compared to a baked potato filled with tuna salad. Eating a peach on its own will produce a more rapid glycemic response than combing it with some almonds.

Glycemic Load (GL).

Just because a food is low GI, it doesn’t mean that you can eat these foods freely; and just because a food is high GI it doesn’t mean that you have to stay away from it totally. The GL was developed by scientists from Harvard University and fine-tunes the GI concept. The GI is a quality rating, while the GL is a quantity rating. The GL of a specific food portion is an expression of how much impact or power the food will have in affecting blood glucose levels. It is calculated by taking the percentage of the food’s carbohydrate content per portion and multiplying it by its GI value. So eating just a small portion of a high GI food, like watermelon, could affect your blood sugar as much as eating too much of a low GI food, like apples. So it’s quality and quantity that affects overall blood sugar control.

Applications for the Glycemic Index

Choosing lower GI foods over higher GI foods can help you achieve better blood sugar control, which means that low GI diets have applications in diabetes prevention and management as well as in the management of hypoglycemia. Sports people and very active people can benefit from the sustained release of energy that lower GI diets can help one achieve. High GI foods are also useful in sports during or after exercise to help correct exercise induced low blood sugar. Stress affects blood sugar control, so people in high stress environments, like corporates will benefit from the effects on low GI diets. The GI has also been used with great success in weight loss diets, because they help reduce the insulin load that can lead to weight gain. Children, and particularly those with learning difficulties and attention deficit disorder do better on lower GI diets.

Making The Glycemic Index Work For You

It is important to remember that the purpose of the GI is not to classify foods as “good” or “bad” but rather to help you learn how to make the right combinations that help you get the most out of your food. While it is always a better choice to choose lower GI foods, you can still make relatively good choices with higher GI foods.

At breakfast time, give preference to low GI breads or cereals. Should you prefer the higher GI varieties, you can add some protein (like an egg), oat bran, or some milk or yogurt, which lowers the GI further.

If high GI foods, like white bread are your thing, combining them with lower GI foods to help balance the meal out. So instead of 2 slices of white bread, you could try eating just one slice and replacing the other slice with a few tablespoons of baked beans and some salad greens. Salads should include a large amount of vegetables and balanced out with a lean protein (like fish, low fat cheese or chicken for example) and accompanied by a low GI starch (like a slice of low GI bread, some legumes, some barley or brown rice, for example).

Make up the bulk of your main meals (about half of your plate) with low GI vegetables and fill about one quarter of your plate with low GI starch (like some wholewheat pasta or sweet potato, for example). Then include some lean chicken, meat or

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fish, or a vegetable protein source from legumes or soya to fill the remaining quarter of your plate.


Most fruits are relatively low GI so they are an ideal between meal snack. Higher GI fruits, like melons, can be combined with some nuts and seeds to help lower the GI. Low GI crackers with protein or fat toppings are also good snack choices

Basic Glycemic Index Guide


Higher Glycemic Index Food Examples

Lower Glycemic Index Food Examples

White, brown and wholewheat breads

Low GI seed breads and sourdough rye breads

Most breakfast cereals, regular and quick cook oats, and regular mueslis

Bran flakes, rolled oats, and Low GI cereals and mueslis that are labelled as such

Pasta: lasagne, penne, fussilli

Pasta: spaghetti, fettuccine, angel hair, any wholewheat pasta

Refined mielie meal

Cold or reheated mielie meal, samp and beans

Baked and mashed potatoes

Boiled baby potatoes in the jacket, slightly undercooked

Short grain sticky rice

Wild rice, brown rice, Tastic Rice, Basmati rice

Tropical fruits (e.g. papaya, banana, melons)

Deciduous fruits (e.g. Apples, pears, plums), citrus fruits, berries

Butternut, pumpkin

Most vegetables including greens

Sucrose, glucose

Fructose, xylitol

All legumes and dry beans

Milk and yogurt


Author: Ashleigh Caradas

* A copy of this article appeared in BUSINESS DAY HEALTH NEWS

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