What is the Glycemic Index?

Foods that contain carbohydrates increase blood sugar levels. The glycemic index ranks carbohydrates on a scale from 0 to 100 based on how much they increase blood sugar levels compared to a rise that would occur from pure glucose.

If a carbohydrate causes a high rise in your blood sugar level it's considered a high GI food and it's digested and absorbed into your bloodstream very rapidly. On the other hand, low GI foods are slowly digested and absorbed, which causes only a low or gradual rise in blood sugar.

Why is the Glycemic Index Important to Diabetes?

When you have diabetes it's essential to keep your blood glucose levels in check. This helps to reduce the amount of insulin your body needs to produce, or the amount of insulin you need to take. Keeping blood glucose levels close to normal also lowers your risk of diabetes complications such as retinopathy or vision loss, neuropathy or nerve damage, foot ulcers, and kidney disease.

In theory, eating foods that have a low GI are better if you have diabetes because they're less likely to cause sharp fluctuations in blood glucose levels. They also improve blood fats in people with both type 1 and type 2 diabetes.

However, using the glycemic index as a guide for good eating when you have diabetes isn't so simple. For more effective management, you need to consider the glycemic load of a food.

What is the Glycemic Load?

The glycemic load is a newer term that takes into account the glycemic index of a carbohydrate food and the amount of that food, which gives a more accurate idea of how it will affect blood sugar levels. By definition, the glycemic load is the glycemic index of a food multiplied by the amount of carbohydrate in a serving of food and divided by 100.

So rather than just focusing on the GI of a food to determine how it will affect your blood sugar levels, you must also take into account how much of that food you're eating.

What Else Affects the GI of a Food?

Aside from the type of carbohydrate and the serving amount, GI is also affected by the other foods that are being consumed at the same time. Most people eat a variety of foods at each meal. If you're eating protein with a carbohydrate, it will affect how quickly the carbohydrate is digested and absorbed.

Other factors to consider include food production and preparation. Where a food is grown, how it's stored and how it's prepared for eating all affect the GI level. For instance, the GI values of rice may vary by 100 percent. Heat, moisture, freezing, and rolling also affect a food's glycemic index.

Also, a person's body chemistry influences how the GI of a particular food affects them. Just like some people may experience allergies to peanuts or shellfish, some people have a makeup that allows their bodies to digest and absorb foods more slowly than others. So, for instance, if you're on a low-GI diet and not seeing a significant different in your diabetes, this could be one reason.

How Does Exercise Affect the Glycemic Index?

Exercise is essential in treating diabetes, especially type 2 diabetes and prediabetes. But evidence of how the GI of foods affect exercise metabolism isn't definitive.

According to a member of the Gatorade Sports Science Institute, Janet Walberg Rankin, Ph.D., eating lower GI foods before exercise can reduce hypoglycemia at the start of a workout, increase fatty acids in the blood, and increase fat oxidation so your body doesn't rely on carbohydrates for energy.

She also points out that the glycemic index of a carbohydrate isn't as important during exercise because insulin response is blunted during exercise. After exercise, however, high GI foods can speed up the replenishing of glycogen stores in the muscle and reduce the levels of insulin you need. However, she cautions that more research is needed.

If figuring out the glycemic index of every food you eat to manage your diabetes is a pain, keep it simple: Remember that the worst GI foods are baked potatoes (not sweet potato) and refined carbohydrates such as, breads, pasta, pastries and sweets. Stick to whole grains as much as possible and eat only two to three servings of fruit each day, preferably not all in one sitting.