Glycemic Impact 101
Here's a quick primer to help you understand the science behind the glycemic index.
Blood Sugar Response in a Nutshell
Quickly digested, high-glycemic-index (GI) carbohydrates (known as "gushers") enter the bloodstream rapidly, causing a surge of glucose. This "gush" of glucose is met with an equalizing amount of insulin to move the glucose into muscle and fat cells. The result is an overcompensation –– and low blood glucose. Looking for a quick fix to the unpleasant hypoglycemic feelings, people often choose another high-GI food, another glycemic surge occurs, and a roller coaster pattern emerges. This leaves the body feeling hungry and fatigued, while inducing fat storage rather than fat burning.
Slowly digested, low-GI carbohydrates ("tricklers") are also metabolized into glucose but their entry into the bloodstream is stretched over an extended period of time. Instead of a glycemic surge, there's a glycemic "trickle." The body responds to a slower, smaller, infusion of glucose with a reduced insulin release. Rather than having too much and then too little glucose circulating in the blood, the body experiences a steady supply of readily available energy. With no hyper- or hypoglycemic conditions to correct, there are no hunger cravings, no energy lulls, and no fat storing. The body has found its comfort zone and rides through it in "cruise control." Once this internal homeostasis is set, the body naturally seeks to perpetuate these conditions, and low-GI eating becomes an easily acquired lifestyle rather than a "diet."
Since its first mention in 1981, the glycemic index (GI) has received erratic support from mainstream organizations. The American Diabetes Association (ADbA) has acknowledged, at times, that various carbohydrates have different glycemic responses and that low-GI foods may reduce blood glucose levels. The ADbA has conceded in recent years that low-GI diets provide a 0.43 percent decrease in A1C over and above the reduction achieved by diets in which only the amount of carbohydrate consumed is considered. The 2007 Nutrition Recommendations for the Management of Diabetes from the ADbA identify monitoring the amount of carbohydrate consumed as key to achieving glycemic control, but also mentions the additional benefit provided by use of the glycemic index. The Joslin Clinical Oversight Committee recommends reducing both the quality (GI) and the quantity (glycemic load or GL) of carbohydrate choices for overweight and obese adults who have type 2 diabetes, prediabetes or are at high risk for developing type 2 diabetes. The American Dietetic Association (ADA) continues to adhere to the traditional exchange/carbohydrate-counting mindset, maintaining that, "for people with diabetes, monitoring total grams of carbohydrate remains the key strategy." The controversy over a robust endorsement of the glycemic index for blood sugar management continues.
Gushers vs. Tricklers
How does one identify gushers and tricklers? Several factors affect the digestibility of a carbohydrate and its GI value. The most important GI determinant is the physical state of the starch. The development of grinding, milling, and other food processing techniques over the past 200 years has had the greatest impact on the quality of the carbohydrates in our current diet. Removing outer fibrous layers and reducing the particle size of grains such as wheat enhances quick digestion. This is why breads, crackers and other bakery products made from finely milled enriched flours have high GI values, while stoneground products that are dense and grainy have lower GI values.
Along with milling and the like, simply cooking in water can have a big impact on the physical state of a starch. The longer a starch is exposed to water, the more gelatinized its particles, the more swollen it becomes, and the faster it turns into glucose. Thus, overcooking any type of pasta, for example, will increase its GI value. The presence of soluble fiber (rolled oats, beans, lentils, apples), acids (sourdough bread, pickled vegetables), and fat and protein are all factors that slow digestion and release glucose more slowly into the blood.
How to Eat More Low-GI Foods
1. Eat high-fiber breakfast cereals like All Bran with Extra Fiber or Fiber One; choose old fashioned, rolled or steel cut oats instead of quick or instant oats.
2. Choose dense, whole grain and sourdough breads whose first ingredient says whole wheat or rye flour instead of enriched wheat flour.
3. Look for whole grain crackers like Ry Krisp, Finn Crisp, WASA, and Ry Vita.
4. Eat five to nine servings of fruits and vegetables every day.
5. Include legumes (lentils, beans) in soups, salads, and dips.
6. Replace white potatoes with yams, sweet potatoes, or new potatoes.
7. Replace refined or puffed starchy snacks with dry-roasted nuts, cooked sugar-free puddings, fruit smoothies made with fresh or frozen fruit, non-fat milk and/or light yogurt, whole grain or bran muffins, or low fat oatmeal cookies.
These suggestions highlight that "using the glycemic index" really amounts to choosing nutritious, low-GI foods, incorporating the USDA's recommendation of five to nine daily servings of fruits and vegetables, and minimizing refined, nutrient-deficient sweets and convenience foods. Low-GI carbohydrates can be gradually integrated into any meal plan; the accompanying health benefits will increase as low-GI choices become more prevalent.
Source: Johanna Burani, MS, RD, CDE, a registered dietitian who has successfully incorporated the use of the glycemic index in her private practice in northern New Jersey since 1993.
Reviewed by Susan Weiner, R.D., M.S., C.D.E., C.D.N. 3/08
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