Glycemic indexes: what are they and how do they affect our health?

Is it already Friday? Where has the week gone?

My week has been pretty uneventful and consisted of; working, climbing, writing and finishing off Smallville lol; good timing because school resumes next week! My courses this coming semester include a pharmacology class, a biochem. Class, and two nutrition classes (one worth two credits). Looking forwarded to them :)!

Here’s a picture taken by my friend Will in Ontario :)

By the end of 2011, the UN stated that non-communicable diseases (including heart disease, obesity and diabetes), for the first time, have outpaced infectious diseases as a main threat to human health around the world. What is causing this shift? Today our sugar consumption has gone way up along with the consumption of high glycemic index foods. Could this be the answer? This blog will be on glycemic indexes (GI) and their implications towards our health, hope you enjoy! :)

Sugar consumption has dramatically increased, being especially prominent in our youth and children. At the same time, the prevalence of chronic diseases such as obesity and diabetes has dramatically increased. Considerable evidence links low GI diets with good health while higher GI diets are associated with chronic diseases. Furthermore, recent work indicates that high-GI foods increase our hunger and decrease our satiety. Today, we have a great availability for energy rich foods. Approximately 35% of U.S. adults fall into the pre-diabetic range, while an estimate 12.0% have diabetes. Diabetes, when diagnosed during midlife, is associated with the loss of 10 years off of lives; much of this is related with diabetes relation to heart disease. Diabetics are at a two to fourfold higher risk for heart disease. According to the National Health and Nutrition Examination Survey from 2009 to 2010, 33% of adult Americans were overweight and 36% were obese!

So how does GI work? GI is widely known yet, for some reason, is controversial in its use; it is a kinetic parameter describing a foods ability to raise blood glucose. Food can be categorized on a scale from 0-100 depending on blood sugar effects and then be put into 3 categories; 1) Low GI(up to 55), 2) medium GI(56-70) and 3) high GI(over 70). Lower GI foods have lower rates of glucose entrance into our blood and therefore a lower insulin response. Slower digested carbohydrate rich diets are associated with a reduced risk for heart disease, diabetes and cataract risk. Before I move on, I think that it’s important to mention that, while table sugar has a GI of 65, white bread’s average GI is around 71.

What determines the GI of a given food?

In order to understand GI’s we have to first understand carbohydrates. Carbohydrates (a.k.a. sugar) can be split up into the following categories; monosaccharaides, disaccharides and polysaccharides. Monosaccharaides include glucose (the main sugar we use for energy), galactose and fructose. Disaccharides (two sugar molecules) include sucrose (table sugar, glucose + fructose), lactose (milk sugar, glucose + galactose) and maltose (a building block for starch, glucose + glucose). Finally, our polysaccharides include our starches (polymers of glucose), and non-starches.

Starch can be divided into rapidly digestible, slowly digestible and resistant; starches with higher amylose content tend to be more resistant to digestion than ones with higher amylopectin. Rapidly digestible starches will raise our blood glucose faster and cause an episode of hypoglycaemia (with an increased risk for insulin resistance and diabetes). Slowly digested starches provide a more sustained glucose release, without the spike associated with rapidly digested starches and with prolonged energy availability (with improvements in insulin sensitivity). And finally, resistant starch is not digested in our small intestine but fermented by our gut micro-flora (beneficial for our colon health). So why have I told you all of this?

Our body can only absorb monosaccharaides, so polysaccharides must be broken down into their monomers (single molecule) before we can use them. Glucose is the easiest monomer for our bodies to use since it doesn’t require further modifications (our bodies use glucose). Fructose and galactose on the other hand require further processing (in our liver) before we can use them. As a result, in sucrose and lactose (glucose + fructose, galactose + glucose), while the glucose can be quickly used, the galactose or fructose molecules will need to be sent to the liver for processing.The need for further processing results in a lower blood sugar spike. GI’s are dictated by the monosaccharaides present in carbohydrates as well as other factors including refinement.Since starches are strings of glucose molecules, depending on their refinement, amylose content and amylopectin content, they may result in a spike in our blood glucose.This is why breads can have a higher GI than sugar (which contains fructose and glucose); so does that mean all grains are high GI?

Grains consist of a large variety of foods, in turn there is a variety of GI’s associated with them. Generally, the more processed or refined a carbohydrate is, the higher the GI (lower GI grains include barley and bulgur wheat). Breads (both white and whole grain) are generally made with pulverized grains rather than cracked grains; as a result, their GI’s are quite high. If you want a lower GI grain, look to ones in a more natural state (e.g. cracked or whole) since it takes longer to digest. Pasta is a bit different, when cooked ‘al dente’ (just tender) and eaten in moderate amounts it has a lower GI than when well cooked (comes down to the ease of digestion). So my answer to the above question, like most things; it depends.

And some concluding thoughts, chronic diseases are reaching epidemic proportions in modern societies; clearly something’s going wrong. While the use of glycemic index is, for some reason, controversial, I believe that they should be used more frequently. Why is the use of glycemic indexes controversial? Why do our food guides continue to have such high refined grain content? Reduced glycemic indexes are associated with a reduction in chronic diseases (including diabetes, obesity, cancer, heart disease, etc.), and are therefore good concepts to incorporate into our diets (Glycemic index reference tables can be found pretty easily online). Hopefully this post has shed some light on glycemic indexes!

Hope you all have a great day!

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Foster-Powell K, Holt S, Brand-Miller J. (2002) International table of glycemic index and glycemic load values: 2002. Am J Clin Nutr;76(1): 5-56.

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