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Glycemic Load: Where Carrots Don't Count
Dr. Ralph Ofcarcik, Ph.D.
Director of Nutrition Services

"First they tell you one thing and then . . . " Sound familiar? More than likely you've heard (or uttered) these words to a friend or coworker regarding the latest nutrition study. For those of us who work in dietary education, nutrition science, historically, has been a challenging, sometimes frustrating technology where periodic conceptual switcheroos are the norm - a non-stop roller coaster ride requiring continuous rethinking (and in some cases scrubbing) of precious tenets that just simply can't stand up to latest findings. You can't get attached to your sacred dietary cows.

At the top of the about-face issues is low-fat vs. low-carb diets. Twenty-five years ago, the health of Americans warranted less fat (and less calories). Unfortunately, the commercial evolutionary version of the low-fat diet was far from healthy. Consumers controlled their fat intake but consumed more calories - mostly from sugar in low-fat desserts and soft drinks (which are fat-free). Nathan Pritikin and Dr. Ornish would not approve. Consequently the current trend away from fat restriction to low-carb lifestyles has merit. Both were right for their times. Other recent doctrine-busters include:

Eggs
High cholesterol foods - like eggs - were once thought to have a profound negative impact on our serum cholesterol. This was a common incorrect assumption.

Chocolate
The dieter's nightmare of old, chocolate, is currently regarded as a health adjunct, decreasing LDL oxidation and improving mood. A chocolate a day may keep the doctor away (but not a pound of Godivas).

Coffee
Twenty years ago, coffee was reported to increase the risk of liver cancer. Current studies suggest just the opposite, i.e. it may reduce the risk.

Alcohol
In one of my older nutrition texts (1987) authored by physicians and Ph.D's from a major university, alcohol consumption was said to increase the risk of heart attacks and strokes - a direct dose-response relationship. Currently, we know that modest alcohol consumption increases HDL cholesterol and is associated with a lesser incidence of both beginning and advanced atherosclerosis.

Vitamin E
Taken daily (200-800 IU's), vitamin E was once thought to ward off hardening of the arteries. Recent research has found it to be ineffective and possibly interfere with some medications.

Currently, one of our most cherished cornerstones may be crumbling. The Lipid Hypothesis, first proposed by Ansel Keyes half a century ago and now the basis for nearly all heart-healthy diets (American Heart Assn., American Dietetic Assn., USDA, etc.), is under fire. A few reputable scientists are publishing compelling arguments against the Lipid Hypothesis, suggesting instead that hydrogenated oils and processed carbohydrates are much more lethal in promoting cardiovascular disease than New York steaks and omelets. (This will be the subject of a future eBlast article).

With the current frenzy to avoid excess carbs, particularly glycemic-spiking sugars and milled grains, the Glycemic Index (GI) has become a part of the health-conscious vocabulary. However, it too may soon be a part of nutrition history. There's a new smoking gun in town, the Glycemic Load (GL), that has caught the eye of many experts. To understand the impetus for change requires a fundamental understanding of both the GI and GL.

The first journal article to be published on the Glycemic Index can be credited to Jenkins et al1, (1981) where 62 commonly eaten foods were compared to glucose in their ability to raise blood sugar. This was the start. Since that time, over 700 additional foods have also been screened, with most of the credit going to Austrailian researchers at the University of Sydney (see www.glycemicindex.com). The modus operandi for testing uses volunteers who fast overnight for at least 2 days (but usually 4 or 6 days). First thing in the morning - on the odd days - they consume 50 grams of carbohydrate from a standard (sometimes white bread but normally a glucose solution). On the even days, volunteers are fed the test foods, which like the standards, contain 50 grams of carbs. On both days, blood sugar levels are plotted (as a curve) for a few hours after consumption. The area under the curve for the test food divided by the area under the curve for the glucose solution, expressed as a percent (i.e. multiplied by 100) is the GI. Foods with a GI of 70 or more are said to be high-glycemic, 56-69 medium-glycemic, and 55 or less low-glycemic. A general impression of many regarding the use of GI tables for diabetic meal planning or treating insulin resistance is that it is helpful, good but not excellent. So why has the GI not enjoyed overwhelming success? I'll give you a hint: To consume 50 grams of carbohydrate would require eating either 3 baked potatoes, 8 rice cakes or 10 carrots! Correcto! . . . the key limiting factor of the GI is it's inherent inability to account for variances in serving sizes.

The Glycemic Load, however, is a natural extension of the GI and does account for normal portions. To compute the GL, simply multiply the GI (as a decimal, not percent) by the number of grams of carbs in a normal serving. For example, high-glycemic carrots (GI = 72) have only 5 grams of carbs in a large carrot. The GL, then is:

Glycemic Load, 1 large carrot = 0.72 (again, expressing the GI as a decimal) x 5
= 3.6

Low GL foods have values less than 10, medium GL's range from 11-19, and high GL's are 20 or more. I'm certain all of us have been warned at some time to avoid glycemia festering carrots - advice stemming from GI research. However, when reevaluated to conform to a normal serving size, say 1-2 large carrots (GL = 3.6 to 7.2), they appear a lot less formidable. Other pleasant surprises (i.e. high-GI/low GL foods) include rice cakes, potatoes, watermelon, cornmeal, and plain scones. For a complete listing of over 770 foods (GI's, serving sizes, and GL's), I highly recommended David Mendoza's website. (Note: Mendoza is a web writer who maintains an excellent website packed full diabetes resources). You can access the chart at www.diabetes.about.com/library/mendozagi/ngilists.htm.

Will Red Mountain Spa scrap the GI tables in favor of portion-specific GL's? Possibly. There are still some lingering GL-related questions, which when answered, will make us feel more receptive. First, it is assumed that there is a direct relationship between carbohydrate consumed in a given food and glycemic expression. It intuitively makes sense, but is it true? Is it possible that glycemic expression is not a direct-dose response relationship? Are there thresholds unique to certain types of food? What is the nature of most relationships? Direct? J or U shaped? J or U shaped reversed? Until these issues are address, we're inclined to continue using the GI where some successes have occurred. (Note: Since use of the GI - which has been effective - inherently assumes a linear relationship between food consumed and glycemic response, I suspect my devil's advocacy toward the GL is a bit naïve, but nonetheless justified.). Whether you trust your intuition and favor the Glycemic Load, or opt for an established dietary tool (Glycemic Index), temper your dietary decisions with a heavy dose of common sense. According to one expert, "There are no bad foods, only wrong portions and proportions".

¹ Jenkins DJ, Wolever TM, Taylor RH, Barker H, Fielden H, Baldwin JM, Bowling AC, Newman HC, Jenkins AL, Goff DV. Glycemic index of foods: a physiological basis for carbohydrate exchange. Am J Clin Nutr 1981 Mar;34(3):362-6.