Jan 23 The Glycemic Index- How it works Filed Under ( , , , , , ) by franca@duke.edu on 23-01-2012
Have you ever seen weight loss commercials claiming their product works using the “science of the glycemic index”, or have a friend who won’t eat white potatoes because they have a high glycemic index? If you are wondering what all the hype is about, then read on. The Glycemic Index is a measure of how much the sugar in certain foods that we classify as carbohydrates (breads, cereals, grains, starchy vegetables, fruits, and sugars) will raise your blood sugar (glucose) levels. Let’s back track a little. Carbohydrates supply energy to your body in the form of glucose, or sugar. When you eat a carbohydrate food it is broken down to glucose which is released into your bloodstream to be used as fuel for your brain, muscles and organs. Some carbohydrate foods cause blood glucose levels to rise sharply and quickly. How does your body respond? When this happens, you have a rapid output of a hormone called insulin – which helps your body use glucose for energy, and glucose is taken up bymuscle tissue or stored as fat. The insulin response causes your blood glucose to drop rapidly. This is what you would consider a blood sugar “spike”. Sounds like a roller coaster ride, doesn’t it? The GI is a ranking of carbohydrate foods based on how quickly they raise your blood glucose levels. Foods are ranked on a scale from 0 to100 based on how they compare to a “reference food”– which is either glucose or white bread. A food with a high GI raises your blood glucose more than a food with a medium or low GI. As a general rule, the more processed the carbohydrate is – think white breads, cornflakes etc.; the higher the GI. While more wholesome foods such as beans and 100% whole grains have lower GI. (You can check out the GI of foods at ). The catch here is that some foods you might expect to have low GI such as oatmeal actually has a higher GI than chocolate, another reason why you should check out the GI database. It’s important to note that the GI is a measurement of thefood eaten alone, and will change when foods are eaten together; for example, if you add butter to your baked potato, that changes the GI of the potato – actually lowering the GI (that’s because fat, along with protein and fiber, slows this process down). Cooking methods may also change the GI of certain foods. Lastly, the effect of the food’s GI on blood sugar varies from person to person since an each person’s glucose response is different. In general, choosing complex, wholesome carbohydrate foods such as100% whole grains, vegetables, fruits and legumes, is still the right way to think about healthy eating. Using the GI may be helpful (especially for specific population groups such as those with diabetes or insulin resistance and serious athletes), but for most of us there is more to consider than just the one number. While knowing the GI of a food is a good place to start, knowing the amount of carbohydrate you are getting in a food based on the amount of that food you are eating(the Glycemic Load) is a more practical and usable tool. So stay tuned for our next installment where we discuss Glycemic Load in more detail.
