The Load Lowdown: A new way of seeing foods may hold promise for weight control and disease prevention
The carrot, it seems, has been rehabilitated.
If you haven't tried The Zone, Sugar Busters or another diet based, at least in part, on the glycemic index, you may not have known that the carrot, once the epitome of healthful eating, had been forsaken. It had. Now it's back. The implications may apply to more of us than we think.
The glycemic index (GI) is a ranking of foods according to their effect on blood-sugar levels; it reveals that not all carbohydrates are created equal. Some researchers and nutrition experts believe that diets emphasizing foods with a low glycemic index may promote weight loss, help control diabetes and lower the risks of getting diabetes and cardiovascular disease.
Foods whose carbohydrates break down slowly release glucose into the bloodstream more gradually, earning them low GI scores. Those that break down quickly trigger fast, high blood-sugar responses, earning high scores on the index. Most legumes, fruits and non-starchy vegetables are on the low side of the index; sugars, refined grains and a few fruits and veggies tend toward the high side. On a scale based on white bread with a GI of 100, peanuts are 21, red lentils 36, an apple 54, chocolate 70, baked potato 121 and a baguette 136. Because of a high GI — 92 — carrots were, in Zone terms, an "unfavorable" food.
But now carrots have regained their stature, on two fronts.
The glycemic index was created as a research tool, not as a practical guide for evaluating foods one at a time. To determine a food's glycemic index, scientists use a standard amount, measured in carbohydrates: 50 grams. However, that doesn't reflect the number of grams in a serving of that food. One baked potato has 37 grams of carbohydrate. A half-cup serving of cooked carrots has only eight grams.
To account for serving size when assessing a food's practical effect on blood sugar, researchers at Harvard have proposed the term "glycemic load" (GL). To calculate glycemic load, simply multiply the grams of carbohydrate in a serving of food by that food's glycemic index. (Although GI values commonly are referred to as whole numbers, technically, they're percentages expressed as decimals — 1.21 for a potato, .21 for peanuts, etc.).
A recent issue of the newsletter Harvard Women's Health Watch ranked some foods by both GI and GL. For a baked potato, the calculation went like this: 37 (grams of carbohydrate in a serving) multiplied by 1.21 (GI) equals 45. That's still high in a ranking of foods by glycemic load. Air-popped popcorn, though, went from a high GI of 79 to a low GL of 4. Corn chips fell from 105 to a moderate GL of 16. Carrots dropped from Harvard's oddly high GI of 131 to a GL of 10. Remember, serving size counts: That's a cup of popcorn, an ounce of corn chips and a half cup of cooked carrots.
And carrots' stock goes up even further. The widely used glycemic indexing of carrots at 92 (not to mention that 131) was faulty, according to Australian researcher Dr. Jennie Brand-Miller, a leader in the field and author of "The Glucose Revolution." She told me by e-mail that a later, less publicized test put carrots' GI at 49, and very recent tests under her watch found boiled carrots to have a GI of 32 and carrot juice 43. That would give carrots a GL between 3 and 4.
"I think the glycemic load is shaping up to be a valuable concept," said Brand-Miller. "A diet with a very high GL should be avoided. This means that the higher the carbohydrate content of your diet, the more important it is that the carbohydrate comes from low-GI sources."
Though a proponent of GI and GL awareness — she's working to develop a program that would allow low-glycemic-index foods to be labeled as such — Brand-Miller cautions against taking it to extremes.
"I don't think we should be necessarily aiming for a diet with the lowest GL," she said. "While the worst choice is a high-cholesterol, high-GI diet, the best choice is still being sorted out."
Glycemic resources
• "Eat, Drink and Be Healthy," a provocative new book by Walter Willett, M.D., chairman of Harvard's Dept. of Nutrition, emphasizes the glycemic index and load. It says the standard USDA Food Guide Pyramid was influenced by special-interest groups and has been proven a dangerous and misleading dietary guide, contributing to the poor state of American nutrition.
Willett proposes a new Healthy Eating Pyramid, which features daily exercise and weight control at its foundation and a diet based on whole-grain foods, plant oils, vegetables in abundance and fruit two to three times a day. At the peak of this pyramid are red meat, butter, white rice, white bread, potatoes, pasta and sweets.
• The article on the glycemic load in the Harvard Women's Health Watch is online at www.health.harvard.edu/newsletters/giload.shtml.
• At www.mendosa.com are glycemic lists ranked both by food and by GI score.
• Many related links can also be found at www.glucoserevolution.com.
A walk on the Fremont side
Today is Car Free Fremont in that Seattle neighborhood. To promote alternative transportation and celebrate the streets as public space, 35th Street and Canal Street between First Avenue and Phinney Avenue are closed from 9 a.m. to 9 p.m. Events include: free workshops on bike repair, safety and maintenance; an art bike and kinetic sculpture rally; free inline skating workshops; a roller disco in the street; construction of sculptural bike racks; a benefit for Bikeworks, a nonprofit bicycle repair shop and after-school program in Columbia City. For more details, go to www.thinksmall.org
Molly Martin is assistant editor of Pacific Northwest magazine. She can be reached by calling 206-464-8243, e-mailing mmartin@seattletimes.com or writing her at Pacific Northwest magazine, The Seattle Times, P.O. Box 70, Seattle, WA 98111.