Wednesday, August 29, 2007

Using Glycemic Index/Glycemic Load to Control Blood Glucose

CheeriosThe primary reason for my change to a lower-carbohydrate diet is to control my blood glucose (BG) and improve my insulin sensitivity, a choice resulting from my recent discovery that my sugars have been silently creeping up over the years. I know I'm succeeding when the number on my BG meter is in the low 100s after a meal.

I'm not pursuing low-carb as a means to lose weight (although, given my experience, if it's weight loss you're after, you'd be throwing away a chance for success if you don't try this), manage my cholesterol (although, low-carb has been shown to increase HDL and lower triglycerides), or pay homage to a Paleolithic diet (thus, I continue to eat the dark meat on poultry, fatty cuts of meat, cheeses, green beans, peas, peanuts and peanut oil, lentils, soy nuts, corn-on-the-cob, pickles, vinegars, and other foods deemed unacceptable on the Paleo Diet).

How do I determine what to eat?
  1. The total carbohydrate in a serving of food (quantity).
  2. The tendency of that carbohydrate to raise my blood glucose, as measured by its glycemic index (GI) (quality).
Fats have very little effect on blood glucose. Proteins have a small effect. Carbohydrates have quite an impact.

There are many types of carbohydrates. Sugars are short-chain or no-chain carbs. Starches are mid-to-long-chain carbs. Those long chains may be either straight (amylose), or branched (amylopectin). Some carbs, such as cellulose, are not digestible by human enzymes and thus are one constituent of "dietary fiber". These and other factors influence how fast a carbohydrate will raise blood sugar. Low GI foods do not raise blood sugar as fast or as high as higher GI foods.

When you combine the effect of items 1 and 2 (quantity and quality) above, you define the glycemic load (GL) of a serving of food.

GL = Carbohydrate (g) x GI / 100

That is, the glycemic load of a serving of food is equal to the total carbohydrate in that food multiplied by the food's GI. If you consider the GI as a percentage then the above result would be divided by 100.

A GL of less than 10 is considered low. A GL of greater than 20 is considered high.

For example:
  • The GI of Ocean Spray Cranberry Juice Cocktail is about 68.1 One half cup has 18g carbohydrate. So, the GL of that 1/2 cup of juice is around 12:
    GL = 68 x 18 / 100 = 12.24

  • The GI of Silk Soymilk, Plain is 18. One cup has 8g of carbohydrate. So, the GL of that 1 cup of soymilk is around 1 or 2:
    GL = 18 x 8 / 100 = 1.44

  • The GI of a medium-sized (7" to 8"), yellow banana is about 51. One banana has about 27g carbohydrate. So, the GL of a banana is around 14.
    GL = 51 x 27 / 100 = 13.77

  • The GI of cooked, medium-grain brown rice is about 50. One cup has about 46g carbohydrate. So, the GL of 1 cup of brown rice is around 23.
    GL = 50 x 46 / 100 = 23

  • The GI of a cooked Russet potato is about 85. One potato (3 to 4.25 in) has about 64g carbohydrate. So, the GL of 1 potato is around 54.
    GL = 85 x 64 / 100 = 54.4
If looking things up in tables or doing math has a similar appeal to you as cleaning bathrooms, you'll be happy to know there are sites like that will do it for you.


Glycemic Load In Action

Below is a comparison of the glycemic load provided by two breakfasts. I chose RB's and mine from yesterday as an example. (See comments under Global Prevalence of Diabetes.) Data on GL was derived from

RB's Breakfast:

1 cup Cheerios, GL = 13
1 tablespoon (0.5 oz.) raisins, GL = 7
1/2 cup 2% milk, GL = 5
1 cup orange juice, GL = 9
Total GL for meal = 34

Bix's Breakfast:

1/4 cup almond/pecan/pistachio/pumpkin seed mix, GL = 2
1/4 cup spaghetti squash, GL = 1
1/4 cup tomato sauce, GL = 2
2 teaspoons grated cheese, GL = 0
1/4 cup blueberries, GL = 2
Total GL for meal = 7
(One large egg's GL = 0. I could have added an egg omelette to the above and still clocked in with a total GL of 7.)

I'm finding when a meal contains a glycemic load of 15-20 or above, my blood sugars stay high for a while. RB's breakfast, which was not so different from how I ate before my recent finding, would cause my blood glucose to rise and stay elevated for hours. Likely, I would also have undesirably higher levels of blood insulin, secreted by my pancreas to compensate for the ineffectiveness of smaller amounts of insulin - amounts which may have sufficed if my cells were less insulin resistant.

From the information above, you can see why I've chosen to severely limit my consumption of whole grains, potatoes, and other starchy foods. I haven't yet signed onto the idea of cutting out entire food groups (e.g. grains), especially when I consider we have a whole planet to feed. But, for me, just 1/2 baked potato, 1/2 cup brown rice, or 1 cup whole-wheat pasta is enough to keep my BG elevated. A Starbucks cinnamon raisin bagel has a glycemic load of 62! I may as well inject glucose directly into my bloodstream.

In answer to Autumn's question from yesterday:
"... what about brown rice and quinoa and whole wheat? What happens to blood sugar if one consumes only whole grains?"
Blood sugar responses are unique to an individual. However, those who have insulin resistance, prediabetes, or have been diagnosed with diabetes would do well to control intake of starchy and grain-based foods, whole grain or not, given their higher glycemic load. Those who do not have those conditions may wish to consider that the long-term consumption of a diet with a relatively high GL was found to be associated with an increased risk of type 2 diabetes and coronary heart disease.
1 A very thorough and comprehensive table of GIs can be found at the International Table Of Glycemic Index And Glycemic Load Values: 2002. You may also check a food's website for this info.
2 Silk Soymilk website.

Photo: Homegrown (Cheerios).

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