Factors that Effect Glycemic Index

While 2 main factors that effect glycemic index are the content of amylose and amylopectin, there are other factors. The glycemic index values for various foods can be influenced by starch, bran, fiber, sugar type, protein, fat, acid levels, processing and cooking methods. Each of these factors can change the speed at which a carbohydrate is digested and then absorbed into the bloodstream.

Let’s take a look at each of them.

Starch – 2 main types

Two main types of starches are amylose and amylopectin. Don’t worry about the details, but this is what you need to know. Amylose is found in food items like kidney beans. The amylose is more slowly digested because it absorbs less water and has tight clumps of starch. This makes it a dripper vs. a flooder like amylopectin. The amylopectin is digested faster and is found in foods like rice and Russet (white) potatoes. The faster the digestion, the faster glucose finds its way into the bloodstream.

Bran – The coating around the wheat kernel.

Wheat kernels are the main part of the wheat plant that we eat. Before modern day processing, the outside coating or bran would be left on and find its way into our food supply. You have most likely noticed some bread with little “chunks” of wheat – they almost look like nuts. The benefit of having whole wheat, bran or stone ground whole kernel breads are that the bran is like a shell. It interferes with the ability of enzymes to grab the starches and digest them. Again, foods with bran will take longer to digest and thus “drip” glucose into our blood stream.

Fiber – more filling and tastes great!

Try this on 2 different mornings. The first day, have a bowl of cheerios. The second day, have a bowl of old fashioned oatmeal – the kind you need to cook for 20-30 minutes. After 2 hours, notice the difference in fullness and hunger. Most people are still full after they eat the oatmeal. The reason is that the oatmeal contains more fiber. It swells in your stomach and makes it harder for your body to digest the food. Foods like oatmeal and apples contain fiber that slows down the digestion and thus slows glucose entering into the bloodstream.

Sugar Type – Four Horsemen

There are 4 main types of sugar found in our diets. They are glucose, fructose, sucrose and maltose. Each of these sugars must be broken into glucose for the body to use it for energy. Glucose and maltose have the highest GI at 100 and 105, respectively. Sucrose still scores high at 60, but fructose clocks in at only 19.

Protein, Fat and Acid – Slow Down

Acid, fat and protein slow down the digestive process. They require longer times for proper and complete digestion and interfere with fast digestion. Because of this, their presence in a recently eaten meal will slow down the emptying of the stomach into the small intestines. Since they slow down the emptying of the stomach, it takes longer for ingested food to be converted to sugar and also reach the blood stream.


Highly processed foods are common today. Most sugars are finely ground – just take a look at raw sugar, table sugar and confectionery sugar (10x) – the particles get smaller and smaller. The same processes are used for most flours. As food is ground finer and finer, two things happen. The particles of food become more uniform in size and results in similar digestion times for the bulk of food ingested. Second, the surface area of the food becomes much larger and thus the food digests more quickly because the enzyme can attack the food more quickly. Increased processing leads to faster absorption into the blood stream.

Cooking Method – What is al dente?

Have you ever made macaroni and cheese? If you overcooked it, it got all mushy. If undercooked, it was still hard in the middle. When cooked just right, your teeth slowly cut through it and it is just right. Well, the mushy, overcooked pasta is the result of the fiber and carbohydrates swelling. Once swelled, the enzymes that break down food in the stomach are able to access the starches and convert them to sugar more quickly. Pasta that is overcooked can have GI values of over 60. The same pasta cooked “al dente” might have a GI value of only 45. Bottom line – don’t overcook the pasta!

The next time you go shopping, consider using these factors that effect glycemic index when making your food selections.

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