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Ask Dr. Gourmet

Which is more important: a food's glycemic index or its fiber?

I am watching my glucose numbers. Should I be more concerned about a food's glycemic index or the amount of fiber in a food? It seems that a food with a good amount of fiber also has a higher glycemic index.

Dr. Gourmet Says...

a plain, baked russet potato

This is a great question. There has been a lot of good research about the impact of a higher fiber diet on helping control blood sugars. We have less information about the impact of glycemic index (GI) on diet and diabetics, but what we have is getting better. One study in 2008 compared a low glycemic index diet with a high cereal fiber diet and the diabetics on the low GI diet did slightly better.

Some issues with that study is that I think it should have been done using a third control group of the standard American Diabetic Association diet. Also, there are more types of fiber than simply those in cereal grains. Both soluble and insoluble fiber should be evaluated.

That said, relying on the glycemic index as a diabetic is probably not a good idea unless you are going to eat very low glycemic index foods. (The low GI foods in studies are chosen very carefully.) But then it's not good to rely on a simple number when it comes to healthy eating.

For instance, a baked russet potato has a GI of 94 (the raw potato is lower) while watermelon is 80. Both are really healthy foods. A Milky Way bar on the other hand has a GI of 62. I don't care what people say about how glycemic index -- watermelon and potatoes are better for you than a Milky Way bar. Likewise, chocolate milk has a GI of 38 and brown rice comes in at 72. Sorry, but I would much prefer my patients eat the brown rice.

The best advice I can give is to look at both values. Choose both a low GI food that's high in fiber. Good examples are quinoa, lentils and other legumes and veggies (lots of veggies).

Here's some more info on glycemic index:

High-glycemic-index diets linked to risk of Alzheimer's Disease
Not So Magic Rice
When the Glycemic Index Doesn't Measure Up
Hunger, Blood Glucose, and the Glycemic Index
Decreasing the Risk of Gestation Diabetes
Never have business meetings right after lunch; or, why carbohydrates make you sleepy

Thanks for writing,

Timothy S. Harlan, MD, FACP, CCMS
Dr. Gourmet