Wednesday, January 20, 2010

Glycemic Index: A Real Shock


I started writing a different post today but was sideswiped by some startling information. Info that I thought I understood and grasped a long time ago. I am sitting here in shock at how much I did not understand the Glycemic Index (GI). A year or more ago I read about it for the first time. It seemed almost common sense. But I totally missed something. I was of the understanding that on the index scale of 1 to 100, table sugar is 100. WRONG! Glucose (blood sugar) is 100.

In a nutshell, the Glycemic Index is a measurement for how carbohydrates affect our blood sugar levels. Carbs that break down quickly, releasing glucose rapidly into our bloodstream have a high GI. Carbs that break down more slowly, releasing glucose more steadily into our bloodstream have a low GI. Pure glucose serves as a reference point, and is given a GI of 100. This information has been thought to be especially important to people with diabetes, but come to find out it is also important for the rest of us. You know that "sugar" high you get, associated with eating crap? There is a physical reason for it. You've just spiked your blood sugar.

Makes me wonder if our assumption that turkey makes everyone tired at Thanksgiving is wrong. Maybe it's the mashed potatoes.

Surprisingly, many starchy foods have a higher GI than table sugar. (I don't quite understand this yet.)

Sugar (sucrose) has a GI of about 68.

Foods with a GI of 55 or lower are considered low GI and foods higher than 55 are considered high GI. An example of some foods that cause our blood sugar to rise more rapidly than white sugar are:

Pretzels: GI 83
Popcorn: GI 72
Rice Crispies: GI 82
Parsnips: GI 97
Pumpkin: GI 75
Rice crackers: GI 91
Wild rice: GI 87
"Sticky" rice: GI 98
100% Whole wheat bread: GI 77
French Baguette: GI 95
English muffin: GI 77

Here's a look at how white potatoes compare to sweet potatoes:

Yam: GI 37 LOW!
Sweet Potato: GI 44 LOW!
White baked potato: GI 85 HIGH!
Boiled Red-skinned potato: GI 88 HIGH!

Yams and sweet potatoes are the obvious choice. From the above list, I just don't understand how pumpkin and parsnips can have such a high GI. Does this mean they are digested quicker than white sugar? How is this possible?

The reason GI matters:

"Your body performs best when your blood sugar is kept relatively constant. If your blood sugar drops too low, you become lethargic and/or experience increased hunger. And if it goes too high, your brain signals your pancreas to secrete more insulin. Insulin brings your blood sugar back down, but primarily by converting the excess sugar to stored fat. Also, the greater the rate of increase in your blood sugar, the more chance that your body will release an excess amount of insulin, and drive your blood sugar back down too low. The theory behind the Glycemic Index is simply to minimize insulin-related problems by identifying and avoiding foods that have the greatest effect on your blood sugar." (3)

I have much to learn about the GI. I am fascinated by the concept that sugar isn't the only thing that causes such a dramatic spike in blood sugar.


Sources:
1 (http://www.lowglycemicdiet.com/gifoodlist.html)
2 (Eat, Drink & Be Healthy, by Walter Willett, M.D.)
3 (http://www.nutritiondata.com/topics/glycemic-index)
4 (Wiki)

*The picture above is a real, sugary espresso chocolate cheesecake that I made for Jeff the day he got a job out here in DC. It's his favorite but a very rare treat. I have plans to try it with honey someday....

8 comments:

Health and Happiness said...

How interesting! I've always been told to look for foods that were low on the GI scale, but never really completely understood it.

will said...

WoW! Perhaps that explains why my 10 year old son has been craving and eating a ton of popcorn since we cut the sugar. I knew yams and sweet potatoes were a better option that white potatoes, but had no idea how much or why.

Farty Girl said...

Yeah it's amazing how few people know about this... but I bet it will be the new health trend sooner or later. I prefer eating low GI because of the fiber content of those foods. Nothing beats a clean gut.

My Year Without said...

H&H-I hope to fully grasp it, too!

will-How interesting!

Farty-I have a feeling it will take off, too. Since there are foods that are making our blood sugar rise more rapidly than table sugar, we definitely need to understand this better!

Iris said...

I'm surprised by pumpkin too! I would have thought that would be low like sweet potatoes...

Marie said...

Here is a good explanation of things like parsnips and such:

"When using the glycemic index, be sure to consider "glycemic load," which takes account of how many grams of carbohydrate a normal serving contains. For example, carrots rank high on the glycemic index, but the amount of carbohydrates you would actually consume in a normal serving is pretty low, only 6.2 grams. Don't avoid carrots (or beets) based on their GI rankings. Unless you eat huge portions, these vegetables will not disturb your blood sugar very much, and they provide important phytonutrients."

This is from Dr. Andrew Weil and can be found here: http://www.drweil.com/drw/u/QAA400579/Confused-by-the-Glycemic-Index.html

My Year Without said...

Iris & Marie-Look for a post soon about the Glycemic Load. It completes the "story" about the Glycemic Index, and must be taken into account so that we are not scared to eat foods like parsnips, carrots or pumpkin.

I am currently reading about both and trying to make sense of it all, then I will write about it!

Heather said...

I am confused by the whole wheat bread! I have always been told to eat whole wheat, but now what? Does this go for whole wheat pasta too?