Glycemic index and glycemic load, Part 2

This is Part 2 of this article. For part 1 go here: Glycemic index and glycemic load – Part 1

Insulin

As a counter measure to elevated blood sugar level the insulin hormone is released to your blood. Insulin enables the transformation of glucose from blood into cells. Larger and the more frequent spikes of blood sugar in your blood the more insulin is released into your blood. This may lead to lower long-term sensitivity of cells to it (insulin resistance).

Glycemic index of different foods Glycemic index and glycemic load are important when we talk about diets.

Since insulin level in blood is increasing and has difficulty lowering blood sugar the pancreas responds with extra insulin. It starts a cycle of elevated insulin levels and reduced resistance to it. This may lead to an increase of fat deposits in your body. These are all reasons for the increased risk of developing type 2 diabetes, obesity and cardiovascular disease.

Balanced blood sugar level is crucial to your health and a normal body weight.

Factors that affect the GI

Chemical Structure:
Some carbohydrates (eg glucose) are absorbed very quickly where others are absorbed slowly (eg. fructose). Glucose therefore has a high GI of 100 where fructose has a very low GI of 19. Regular sugar (which you put in coffee for example) is a disaccharide consisting of glucose and fructose molecule and therefore has an average GI of about 60.

Physical structure:
Wholegrain cereals have a lower GI than non-whole grain cereals. The reason for this is that the shell that surrounds the dehulled grain is a natural barrier for the enzymes. Therefore, whole-grain rice has a lower GI than white rice which has the shell removed, or lower than the the rice wafers. Also an important role in determining a GI has a particle size (the smaller they are, the higher is the GI). Wholegrain wheat mash (whole seed) therefore has a lower GI than wholemeal wheat flour, where the particles are very fine – starch decomposition is also faster. This is also the reason that white and wholemeal bread can have about the same GI. Pasta made from white flour has a relatively low GI of about 50. Pasta is a kind of exception as it is the only product from white wheat flour that has a low GI.

Age of product:
The maturation process changes the starch into disaccharide maltose, which has a high GI (105). In one study it was found out that the GI of a fresh bananas is about 43, but for an old banana (not yellow anymore) a GI can go as high as 75.

Food processing (heat):
Baking and cooking weakens the bonds between molecules, the food softens and becomes more easily digestible, the foods GI therefore becomes higher. The more intense the heat at which we process the food, the higher the GI. Baked potatoes have high GI (85) whereas cooked potato has a quite low GI (of around 50). Very well cooked pasta has a much higher GI than pasta prepared al dente.

Fiber, fat or acid:
Fiber slows down the activity of digestive enzymes so that the starch breaks decompose longer than otherwise would. Fat and acids slows down emptying of gastric.

Glycemic load

Unfortunately, the GI system metric has flaws among which the most striking flaw is that it ignores the actual food intake (in grams). This quantity may be quite unrealistic in practice – may be greater or less than the amount that you normally consume. To obtain 50 grams of carbohydrates in carrot for example (as it is required to determine the GI) one should consume more than 600 grams of carrots, which is much more than you usually eat in one meal.

Scientists from Harvard introduced a more accurate assessment of the impact of the food consumed in a rapid increase in blood sugar and insulin – a glycemic load (GL). The calculation takes into account the actual intake of food (a typical serving) and, like GI system, classifies food into three groups.

Glycemic load chart
Glycemic LOAD Value
High 20 or more
moderate from 11 to 19
low 10 and less

Glycemic load GL value is calculated by dividing the GI of food by one hundred and multiplied by the grams of carbohydrate in the portion of food that can be obtained. To determine the GL we need to have information on the GI of food and the amount of useful carbohydrates in one portion. GL of food is in this sense its GI, which is set to a specific portion.

An example of GL:

Glycemic load chart
High GI, Low GL High GI, moderate GL High GI, High GL
Piece of white bread (25 g) A slice of watermelon (300 g) Baked potato (200 g)
GI: 70 GI: 72 GI: 85
Portion: 25 g Serving: 300 g Serving: 200 g
OH content in 100 g: 48 g OH content in 100 g: 6 g OH content in 100 g: 21 g
OH content of the portion: 12 g OH content of the portion: 18 g OH content of the portion: 42 g
GO: 70/100 x 12 = 8.4 GO: 72/100 x 18 = 13 GO: 85/100 x 42 = 36

All three products have a high GI, while their GL varies. Variable affecting the GL is the portion size – GL increases with portion size (GL rises) and lowers with smaller portion size (GL is reduced).

What does GL tell us?

GI tells us what impact will food, that we are to consume, have on blood sugar level. GI is valid for 50 grams of obtainable carbohydrates, where such portion is not always the usual portions we eat (the carrot mentioned above). Therefore GL is more appropriate than GI – GL takes into account the real portion size. For those of you who forgot – GI is glycemic index, GL is glycemic load. We must also consider all the factors above – see Factors that affect the GI.
A lower GI does not necessary mean that the food is more healthy. It is also difficult to find out the GI of a food with mixed ingredients.

Planning a healthy meal /diet

When planning a balanced and healthy diet there are more important factors to consider than GI. You should pay attention to what kind of food you consume. It is advisable to consume a lot of unprocessed foods such as wholegrain cereals and flakes, vegetables, legumes and nuts, some quality protein foods and foods that are a source of healthy fatty acids.

It is also recommended to reduce the consumption of processed foods that include a lot of fat and sugar and drinks that contain a lot of sugar (like Pepsi or Cola). With all this in mind we must also never forget to eat our meals on a regular basis (every few hours or so). So when planning an appropriate diet it is always wise to do that with a lot of common sense. Don’t bother yourself too much with glycemic index and such stuff.

End of the article.


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