Glycemic Index- How Accurate is it?

The glycemic index is gaining a lot of speed as a new health trend. We are seeing more and more articles on the topic and even seeing new diet and weight loss programs using the concept. While the glycemic index is a great tool to use it isn't as black and white as it may appear.

What is the glycemic index?

The glycemic index, or GI, measures how high your blood sugar rises after eating 50 grams of carbohydrate. So eating 50 grams worth of white bread compared to 50 grams of sugar (sucrose). The higher the GI value the quicker you absorb the carbs from that food. The lower GI means it has slower absorption resulting in lower blood sugar and insulin response. For the most part this goes hand in hand with any healthy eating plan as the higher GI foods tend to be high sugar foods and refined products like white bread. The lower GI foods include more of the whole grain products, fruits and vegetables.

However, this isn't as straight forward as it sounds.

The GI is only based on eating that one food. We typically don't sit down and eat a several slices of bread or a cup of rice. Most often we are eating them in combination with other foods. Once you add in other foods…more carbohydrate foods, fat, and protein the GI of that entire meal will change.

Things that affect the GI of a food include:

- The other foods eaten at the same time- protein and fat can alter the absorption time
- Preparation of the food: cooked, uncooked, seasoned (i.e. al dente noodles have a lower GI than well cooked noodles)
- Your body's unique reaction to the food
- Ripeness (a ripened banana will have a higher GI index than an unripened one)

The GI index is a great tool as a general guideline, but nothing to look at as black and white. For example, carrots are a high GI food, but this doesn't mean you are going to have a large blood sugar spike and gain weight because you had some on your salad (despite what many fad diets may tell you). This isn't a reason to avoid carrots. Think about it this way. To eat 50 grams of carrots you would need to eat 10 cups in one sitting. You'd have to really love carrots to accomplish that. :-)

For a more accurate picture the GI load was introduced.

This is based on the carbohydrates in a typical serving size of that food. This allows us to get a clear picture that eating a cup of carrots or watermelon is not going to raise our blood sugar in comparison to eating 50 grams of that food. To find the GI load use the following equation:

GI value of a food x number of carbohydrates per serving = GI load

In the end it is a good tool to use as a guideline as it does promote more high fiber, whole foods while limiting the refined food products.

About the Bogger:

Meri Raffetto is a Registered Dietitian and founder of Real Living Nutrition Services. Learn about our online weight loss programs here!