What is the Glycemic Index (GI) all about?

A Quick look at the topic

The glycemic index (GI) is a relatively new nutritional tool used to fine tune carbohydrate intake. It is a measure of the real physiological response to food, giving an indication of the rate of absorption of carbohydrates in foods.

Using this glycemic index information, one can easily differentiate between fast release, and slow release carbohydrates, which enables one to optimise 'fuel' levels in the body.

This is of particular relevance to sportsmen and women, slimmers and those with diabetes. Eating mainly slow release (Low GI) carbohydrates before a sporting event, ensures good 'fuel' levels in the early stages of the event, as well as preventing the dreaded sports induced hypo's afterwards. Re-fuelling with fast release (high GI) carbohydrate drinks, maximizes glycogen stores immediately afterwards, preventing exhaustion, hypo's and resulting in better recovery after the event.

In diabetes optimum blood glucose control can easily be achieved if mostly slow release carbohydrates are eaten in the correct amounts.

And in slimmers, by preventing surges of blood glucose levels, by eating mostly low GI (slow release) carbohydrates, the stimulation of fat STORAGE is prevented. Insulin, the hormone that helps to clear glucose from the blood is also the hormone that stimulates the body to store fat. Thus the more fast release carbohydrates are eaten, the more fat is stored.

Implementing the GI is easy when using the correct ingredients

Rolled oats contain soluble fibre that lowers cholesterol and effectively lowers the GI of meals.		Oat bran contains soluble fibre that slows down glucose absorption. Up to half of the flour in any batter can be replaced with oat bran.
		Wholewheat Pronutro gives good texture to baked goods and lowers the GI.
Mashed butterbeans can replace half of the high GI cake flour in cake recipes.		High Fibre Cereal adds bulk and fibre to batters, without to much increase on the glycemic load of the recipe.

Sweet potatoes are full of soluble fibre and can be added to batters and raw or cooked		Plain or flavoured low fat yoghurt in batters gives depth of flavour, improves texture and lowers the GI
		Low fat or skim milk is better in dishes than water
Mashed butterbeans can replace half of the high GI cake flour in cake recipes.
		Grated raw apple or canned pie apples can replace some of the fat and sugar in a batter. Apples are an effective and cost effective way of lowering the GI of all baked goods.

A more in depth look at the topic

The Glycaemic Index (GI) is a rating of foods according to their actual effect on blood glucose levels. It is not a test carried out in a chemical laboratory.

To determine the glycemic index of foods, the foods are eaten by individuals, and their blood glucose levels tested after eating, to assess the effect of the food on blood glucose levels. In other words the glycemic index gives us an indication of how different foods affect the body’s “petrol” levels.

One could say that the GI of a food represents its blood glucose raising ability.

Introduction

In the past, it was assumed that complex carbohydrates or starches, such as potatoes, mealiemeal (cornmeal) and bread, were digested and absorbed slowly, resulting in only a slight rise in blood glucose levels. Simple sugars, on the other hand, were believed to be digested and absorbed quickly, producing a large and rapid rise in blood glucose levles. Today, we know that these assumptions were incorrect, and that the general public, as well as diabetics, no longer need to avoid sugar altogether, provided it is used correctly. In fact, table sugar has a slightly more favourable effect on blood glucose levels than for example, potatoes, SA standard bread or rice cakes.

As early as the 1930’s scientists challenged the traditionally held view that the metabolic effects of carbohydrates can be predicted by classifying them as either “simple” or “complex”. In the 1970’s, researchers such as Otto and Crapo, examined the glycemic impact of a range of foods containing carbohydrates. To standardise the interpretation of glycemic response data, Jenkins and colleagues of the University of Toronto, Canada, proposed the Glycaemic Index (GI) in 1981.

This work disproved the assumption that equivalent amounts of carbohydrate from different foods cause similar glycemic responses ( the same rise in blood glucose levels). Furthermore, the researchers concluded that the carbohydrate exchange lists that have regulated the diets of most diabetics, do not reflect the physiological effect of foods, and are therefore no longer sufficient in controlling blood glucose levels! Both the amount of carbohydrate, and its rate of digestion and absorption (the glycemic index) determines the physiological response of the body.

Research done all over the world since then, confirms that the new way of ranking foods according to their actual effect on blood glucose levels is scientifically more correct. Consequently the Glycaemic Index (GI) was developed, whereby foods are ranked on a scale from 0 – 100, according to their actual effect on blood glucose levels. In South Africa, glucose is taken as the reference food and allocated a GI value of 100, since it causes the greatest and most rapid rise in blood glucose levels. All other carbohydrate foods are rated in comparison to glucose. Since the GI is a ranking of foods based on their actual effect on blood glucose levels, instead of on assumptions, it is much more accurate to use in the regulation of blood glucose levels.

Using the glycemic index (GI) concept, those suffering from diabetes or low blood sugar (hypoglycaemia), slimmers, children with Attention Deficit Disorder and sportsmen, can all optimize their blood glucose control.

By using the GI concept in combination with low fat eating, both triglycerides and blood pressure can be lowered and HDL-cholesterol (the “good” cholesterol) can be increased. For those wanting to lose weight, the increased satiety given by the lower GI foods, and the fact that less insulin (a hormone that also encourages the body to store fat) is secreted by a low GI diet, results in better fat loss. Even people suffering from cancer, gout and irritable bowel syndrome can benefit from low fat eating and the GI concept.

Remember, foods with a low GI, release glucose slowly and steadily into the bloodstream and do not over stimulate insulin secretion.

High insulin levels are implicated in all the diseases of our modern lifestyle such as high blood pressure, high cholesterol, high triglycerides, diabetes, hypoglycaemia, ADHD, obesity and coronary heart disease (CHD).

HOW THE GLYCAEMIC INDEX IS DETERMINED

In order to find out the GI of a given food, the food has to be consumed, and the blood glucose levels tested after eating the food. For GI testing purposes, the test food must contain exactly 50g of carbohydrate. The amount of food that contains 50g of carbohydrate varies greatly. For example, two dinner plates full of spinach would contain 50g of carbohydrate, but only 2 tablespoons of jam contain 50g of carbohydrate.
The test food is eaten by a specially trained team, within 15 minutes. Blood glucose levels are measured before eating the food and then every 15 minutes after eating the food for two to three hours, and recorded. The blood glucose (glycemic) response of the test food is then compared to the glycemic response of each tester to 50g pure glucose and it is the ratio of the test food compared to glucose that gives us the glycemic index of each food.

Sometimes bread is used as the reference food instead of glucose. The problem is that breads can vary and so it was decided that glucose (which is standard throughout the world) would be used as the reference food in South Africa.

When looking at different GI lists, be very careful to check which reference food was used in the determinations of the GI values, as different reference foods used in the testing could create the impression that some GI values from different sources seem to differ. In addition, many authors mix up the two without realizing it!

To convert a GI with bread as the reference food, simply multiply the value by 0,7. To convert from glucose as the reference food, to bread, multiply by 1,43.

GI conversion factors for different reference foods

Glucose to bread x 1,43

Bread to glucose x 0,7

Often the GI of a given food is not what one would expect.

For example, the GI of South African standard brown bread is 75 - 80, whereas that of sweetened low fat fruit yoghurt is only 33. Previously one would have assumed that the yoghurt with the sugar in it, would result in a sharper rise in blood glucose after ingestion. But when tested in real people in real life situations, the opposite was found to be true. For this reason all carbohydrate containing foods need to be tested in real people in order to determine their GI. By guessing the GI of a food, one could be very far out.

The GI of over 800 foods has been determined worldwide and more foods are being tested on a weekly basis, overseas as well as in South Africa. For a complete reference guide on the glycemic index of foods commonly used in South Africa, see The South African Glycemic Index Guide by Gabi Steenkamp and Liesbet Delport, available in most bookstores in South Africa or it can be ordered from this website.
To order Click here.

Ongoing studies are revealing that the body’s responses to food are much more complex than originally appreciated. The following factors have an influence on the digestion and absorption of carbohydrates, and thus on how carbohydrate foods affect blood glucose levels. In other words, these factors affect the glyemic index of the food, which is the measure, on a numerical scale from 0 - 100, of how carbohydrate foods affect blood sugar levels.

Factors affecting the Glycemic Index of foods

Gelatinisation of starches	Gelatinisation of starches occurs when the starchy food is exposed to liquid and heat (ie cooking). The water binds with the starch in the presence of heat and expands the starch granules. When we boil potatoes, the heat and water expand the hard compact granules, (which make raw potatoes difficult to digest), into easily digestible swollen potato granules. Some granules actually burst and free the individual starch molecules, and this is the reason why potatoes have a high glycemic index – they are easy to digest and absorb.
Particle size	Intact grains such as whole wheat, barley, whole corn and whole rye have much lower GI values than flours (tiny particles) made from the same grains.
Processing	Milling, beating, grinding, mixing, mashing and refining foods raise the GI of that food.
The chemical composition of the starch	Starches, such as rice, can have different types of starch structures which affect their digestibility. Some types of rice such as Basmati rice, have a higher amylose content. Amylose is made up of long straight chains of glucose molecules which are packed closely together, which are more difficult to digest. Other rice, with a higher amylopectin content, is much easier to digest and thus has a higher GI. Amylopectin are branched chains of glucose that do pack closely together and are thus much less dense and easier to digest.
Fibre: type and content	Foods containing soluble fibre, such as oats and legumes, have a lowering effect on the GI because they delay gastric emptying. Insoluble fibre such as that found in digestive bran, on the other hand, has very little effect on the digestability and absorption of the carbohydrate foods. Thus foods containing bran do not necessarily have a lower GI than those foods without the bran. For example South African standard brown bread and white bread both have high GI values.
Sugar	Sugar may lower the GI of foods that have a very high GI because the sugar competes with the starch for the liquid for gelatinization. For example rice crispies have a high GI. When they are sugar coated, the GI is lower and thus cocopops and strawberry pops have lower GI values than rice crispies! Likewise sugar free Weetbix has a higher GI than the ordinary one with the sugar. As mentioned above, sugar can also lower the GI of baked goods, since it is inclined to bind with the fluid in baking, preventing it from binding with the flour and thereby preventing gelatinisation.
Protein and fat	The presence of protein and fat in food may lower the GI. However, it is not advisable to add fat to lower the GI of foods for health reasons. Excess protein tends to wear out the body’s insulin; and fat has the effect of decreasing the effectiveness of insulin. Protein also overtaxes the kidneys and high protein intakes can lead to osteoporosis, arthritis and gout .
Anti nutrients	Phytates, lectins and polyphenols (tannins) normally slow digestion and thereby decrease the GI. These are found in many vegetables and fruits
Acidity	The more acid a food, the lower the GI of that food. For example, beetroot salad with a vinegar dressing will have a lower GI than hot cooked beetroot without the dressing.
Cooking	Cooking usually increases the digestability of the food, and would thus have the effect of raising the GI of that food.
Resistant starch	When starches are cooked and then cooled, the crystalline structure within the food changes to resistant starch which is more difficult to digest. Thus cold cooked starches, (eg boiled, cold potatoes in a potato salad) have a lower GI. This is especially true for mealiemeal. Thus cooked cold maize porridge has a lower GI than the hot freshly prepared porridge.
Speed of eating	Studies have shown that blood glucose levels rise less rapidly when eating more slowly.

Some examples of the GI of South African foods

SLOW RELEASE CARBOHYDRATES (low GI)

Legumes: baked beans, sugar beans, lentils, etc.
Oat bran
Barley
Stampkoring (wheat rice),
Dense & heavy breads
Pasta (Durum wheat)
Tastic rice, Brown rice
Sweet potato
Wholewheat Pronutro: apple bake and original
Hi-Fibre Bran, Fibre Plus, BranFlakes
Deciduous fruits: apples, pears, grapes, etc
Citrus fruits: oranges, grapefruit, naartjies, etc
Vegetables (with a few exceptions)
Yoghurts: low fat, fruit and plain

INTERMEDIATE RELEASE CARBOHYDRATES (med GI)

Cooked oats porridge
Basmati rice
Couscous
Baby (new) potatoes
Original Pronutro
All Bran Flakes
Sweetened refined cereals with milk
Ryevita, rye breads (wheat free)
Tropical fruits eg banana, mango, litchi, pawpaw
Sultanas
Raisins
Fruit bars
Beetroot
Marog
Sugar
Raw honey
Jam (50% fruit content)
Fruit cordials, eg Oros, Soft drinks eg Coke, Fanta
Fruit Juices – most flavours

FAST RELEASE CARBOHYDRATES (HIGH GI)

Mealiemeal & other porridges
Sticky rice
Potatoes
Refined cereals: rice crispies, cornflakes, Weetbix,
Rice cakes, Corn thins
Breads: brown, white & whole wheat
Bread rolls, pita bread, etc.
Flours: wheat, cake, corn, potato, rice
Melons: watermelon, spanspek, sweet melon
Sports drinks: Energade, Sportsade, Game, Lucozade,
Sweets

Note: Product formulations differ from country to country even though they may have the same name

For example:

All Bran in Australia is very different to the All Bran Flakes in South Africa. In fact, the South African Kelloggs All Bran Hi-Fibre, commonly known as Hi Fibre Bran is the most similar to the Australian All Bran in its formulation (recipe). The Australian All Bran and the South African Hi Fibre Bran have almost the same GI (42 and 43 respectively). But all Bran Flakes in South Africa have a GI of 69.

Thus, be very careful which GI tables you use, stick to those for the country you live in.

HOW TO MAKE THE GLYCAEMIC INDEX WORK FOR YOU

All foods that have a GI of 55 or less are slow release carbohydrates and classed
as LOW GLYCAEMIC INDEX FOODS.

They are the best choices in preventing a large rise in blood glucose levels. The low GI foods are more satisfying and do not cause the release of as much insulin as high GI foods do. Therefore low GI foods also prevent the huge drop in blood glucose which occurs after the initial rapid rise in blood glucose levels after eating high GI foods.

High GI foods elicit a huge insulin response, the body’s way of coping with the sudden, sharp rise in blood glucose. Often this insulin response is too much, and blood glucose levels then rapidly fall to below the starting point. A condition known as hypoglycaemia. This swing from very high to very low blood glucose levels, due to hyperinsulinaemia, is now believed to be a contributing factor to most of the lifestyle diseases. These diseases are actually caused by high insulin levels in the blood and could be prevented to a large extent if the general population would consume low fat, low GI foods. Researchers regard all foods with a GI of 62 or below as “safe”, even though the theoretical cut off point for a low GI food in South Africa is 54.

Intermediate GI foods are those with a GI between 55 and 70.
They are the best choice in the following cases:
after low intensity exercise of short duration, in the morning after exercising the previous night, or directly after moderate activity in diabetics.

Foods with a GI higher than 70 are called high GI foods. High GI foods are excellent for the prevention of fatigue and hypoglycaemia in regular sportsmen after doing moderate to high intensity exercise ( for example, sports drinks such as Powerade, Energade and others).

High GI foods should, however, be avoided by diabetics under normal circumstances, but are completely safe for diabetics after strenuous exercise, lasting 2-3 hours. High GI foods are also useful during a LOW blood glucose “attack”. Any person wishing to have sustained energy during exercise, should not consume high GI foods before exercise or when they are inactive, but rather have low GI foods before exercise and during periods of inactivity.

Above is a sample table of the South African low fat foods that have been tested for their GI values. The list is by no means complete as GI testing only started in South Africa in 1998, and foods are being tested at this very moment.

For more information on the Glycaemic Index of South African foods contact the authors, Gabi Steenkamp or Glycaemic Index Foundation of South Africa website; wwwgifoundation.com