Balancing Act
By: Liz Brown
A measure of the effect of carbohydrates on blood sugar levels, the glycemic index is a powerful tool for eating right and maintaining optimal health.
Not all carbohydrates are alike. And even though good nutrition sense has you watching your intake, you still need to eat your share to maintain optimal health. Question is, which ones are the right choice for you? One way to measure their impact on your health is through the glycemic index (GI)—a relatively new tool that's gaining acceptance as an important variable in the nutrition equation. Excess carbohydrates can contribute to weight gain, but that's a secondary effect—first they cause a spike in blood sugar levels—and this is what the glycemic index was designed to measure. Even if losing weight isn't your goal, paying attention to how foods influence blood sugar provides other dividends, including more sustained energy levels, clearer thinking, and better health in the long run.
Rising Signs
Devised in 1981 by a team of scientists at the University of Toronto to
establish the ideal foods for diabetics, the glycemic index (GI) figures
prominently in today's diet discussions, whether for weight loss or optimal
energy. The GI assigns a number (from 0 to 100) to food based on how fast and
how far blood sugar levels rise after you've eaten it. More than 300 carb-based
foods have been measured so far; fat and protein aren't factored in because they
have little effect on blood sugar. In order to use carbs for energy, the body
breaks them down into glucose (sugar) during digestion. But some carbs, those
with a low GI rating, break down slowly, causing a gradual release of glucose
into the bloodstream and a steady increase in blood sugar levels. Other foods
get a higher GI rating because they break down more quickly, causing a fast
delivery of glucose and dramatic rise in blood sugar levels.
Several factors determine how carbohydrates impact blood sugar. Foods that are overprocessed, like instant oatmeal, tend to have a higher GI than those left in their natural state (bran, for instance) because fiber—which slows the breakdown of a carbohydrate—is stripped away during processing. Riper fruits and vegetables typically have a higher GI than their less ripe counterparts. The type of starch (potatoes are the biggest offenders), in addition to fat and acid content, also determines the subsequent spike in blood sugar. Overall, a low GI diet emphasizes carbohydrates that are filling, nutritious, high in fiber, often low in calories, and commonly recommended for weight loss and maintenance: whole grains, legumes, vegetables, fruits, and certain types of bread, pasta, and rice. But the health benefits of following a low GI diet reach far beyond shedding a few pounds.
Low GI foods tend to offer more sustained energy throughout the day, and along with this comes clearer thinking. The drastic rise in blood sugar caused by some foods is inevitably followed by a fall, resulting in erratic energy levels. These peaks and valleys can lead to mild mood disturbances, says Brian Zehetner, a registered dietitian at Canyon Ranch SpaClub at The Venetian in Las Vegas. As a result, clear thinking sometimes becomes difficult. "High GI eating patterns can also increase the uptake of tryptophan in the brain," Zehetner explains. The result is a spike in serotonin, a neurotransmitter that has a calming, almost sleeplike effect—not exactly an energizing diet.
A growing body of research suggests that a diet high in foods with a low GI may have long-term health benefits apart from the advantages of sustained energy. Eating this way appears to protect against heart disease by encouraging weight loss and maintenance, while keeping cholesterol levels in balance. A low GI diet can also decrease the risk of Type 2 diabetes, a disease in which the body loses its ability to control blood sugar levels.
Some food cravings are also blamed on high GI foods. The crash in blood sugar they precipitate is thought to cause an instinctive need for more carbohydrates to bring levels back up, generating a cycle of overeating that ultimately leads to weight gain (especially the layer that seems to congregate in your middle). Low GI foods, on the other hand, maintain blood sugar levels, and since many are also high in fiber and very filling, keep appetites in check.
Another Piece of the Pie
Glycemic index ratings are worth considering when choosing nutritious foods, but
they don't tell the whole story, notes Zehetner. "We also need to look at
nutrient density," he stresses. "In other words, how many specific
nutrients does the food have, including vitamins, minerals, antioxidants,
phytochemicals, fiber, etc." And just because a food has a moderate or high
GI, like bananas, doesn't mean it's inherently unhealthy—especially if it
offers substantial nutrients that contribute to good health.
In addition, the glycemic index doesn't account for the quantity of carbohydrate in a given food; it only factors in the quality of carbohydrate and how that carbohydrate affects blood sugar. (GI compares the impact of carbohydrates in each food gram for gram, not by serving size of each food.) Some foods with a relatively high GI contain a small amount of carbohydrates per serving and may not have such a dramatic effect on blood sugar after all. A measure called glycemic load (GL) factors in both GI and carbohydrate content to predict the body's overall response to a food or meal. Watermelon is a good example of a fruit with a high GI (72) but a low GL (4); the carbohydrate it contains is broken down quickly to glucose, but the carbohydrate content of watermelon is low, so it's not likely to cause the spike in blood sugar associated with high GI foods.
Jeannette Jordan, a registered dietitian in South Carolina and spokesperson for the American Dietetic Association (ADA) agrees that the GI has some flaws. She doesn't usually use the index in counseling her patients about weight management and diabetes due to its variability and unpredictability. The GIs of some foods vary between tests, and it's hard to predict exactly how additional factors—cooking method, food combinations, individual metabolic variation, and so on—alter the overall effect of meals on blood sugar levels. In addition, different kinds of potatoes, oats, and rices have different GI ratings due to variations in the kinds of starches they contain. "Although there are flaws in using glycemic index or load," says Roberta Anding, a spokesperson for the ADA at Baylor College of Medicine, "no one would argue that eating a plate full of vegetables and whole grains is a fad, or unhealthy."
Relying on a variety of nutritious foods in moderate amounts, combined with
regular exercise and a healthy lifestyle, remains sound advice for achieving
adequate energy levels, a healthy weight, and long-term health. But the true
balancing act is learning to listen to the needs and rhythms of your own body.
The glycemic index provides a glimpse into its inner workings, and armed with
this knowledge, you'll be better able supply it with the right fuel for ultimate
wellness.
Designing a meal plan that helps you feel your best is that much easier with this food ranking system. The glycemic index (GI) labels carbohydrates according to their immediate effect on blood sugar levels; glycemic load (GL) factors in the amount of carbohydrates in each serving, producing a lower number that signifies a more gentle rise in blood sugar. Use them in good health.
EAT LESS Foods that are processed or high in starches and carbohydrates have the biggest impact on the rise and fall of blood sugar. Try to avoid them whenever possible.
FOOD GI GL Couscous 65 23 Bagels 72 26 Waffles 76 39 Corn Flakes 81 21 Russet Potatoes 85 26 Dried Dates 103 42 HIGH:GI=70 OR MORE; GL=20 OR MORE
MODERATE This group of foods can cause a slight spike in blood sugar levels, and although they're by no means unhealthy, it's a good idea to watch your daily intake.
FOOD GI GL Spaghetti 42 20 Muffins 60 13 Sweet Potatoes 61 17 Beets 64 5 Cantaloupe 65 4 MODERATE: GI = 56–69; GL = 11–19
EAT MORE These foods have a low glycemic index and a low glycemic load, making them excellent choices for regulating blood sugar and energy levels.
FOOD GI GL Peanuts 14 1 Red Lentils 26 5 Chickpeas 28 8 Strawberries 40 1 Oranges 42 5 Carrots 47 3 Bananas 51 13 LOW: GI = 55 OR LESS; GL = 1–10