Cereal Clues Health Article

I've long known that a breakfast of old-fashioned, slow-cooking oatmeal fills me up until lunchtime, while a bowl of corn flakes—with roughly the same calorie count—finds me craving a snack within a few hours. Likewise, whole-wheat pasta and lentils at lunch stick with me until suppertime, but if I eat mashed potatoes instead I'll find myself ravenous by midafternoon. All my choices seem healthy, but some have more holding power than others.

When I first read about the glycemic index, I had one of those Aha! moments. Simply put, the glycemic index ranks foods containing carbohydrate by how quickly they are digested and how much they elevate blood sugar (glucose). By testing blood-sugar levels in humans after they've eaten various foods, scientists in Canada, Australia and elsewhere have assigned glycemic index (GI) ratings to many foods. Pure glucose, the usual benchmark for comparison, has a GI of 100.

The ideal carbohydrates for our bodies are those that are digested slowly and therefore provide a long, steady supply of energy. These foods rank low on the glycemic index scale and include apples (38), pumpernickel rye bread (50), whole-wheat spaghetti (37), dried beans (30) and lentils (30).

In contrast, high-scoring foods digest quickly and send a rush of glucose into the bloodstream. Examples of high-GI foods are corn flakes (92), mashed potatoes (74), doughnuts (76) and white Wonder Bread (73).

High blood-glucose levels are of extreme concern for those with diabetes, but can also be bad for the rest of us. Glucose spikes trigger rushes of insulin, the hormone that ferries glucose into cells. The surge of insulin quickly moves the glucose out of the bloodstream and into our cells, but the consequent drop in blood sugar triggers a feeling of hunger. Even more troubling, continued high insulin levels can promote fat storage, weight gain and can lead to heart disease and stroke by causing higher blood fats (triglycerides), lower good cholesterol (HDL) and elevated blood pressure.

Why are some carbohydrates better than others at helping avoid these glucose-insulin spikes, crashes and follow-up hunger? Most foods with low GI values have larger particle sizes and coarser, more fibrous textures. They require more chewing and move through the digestive tract slowly. On the other hand, potatoes and grains finely ground into flour or pulverized and formed into cereals have small food particles that are digested very rapidly—almost instantly, in fact. Interestingly, cooking methods can change the glycemic effects of foods. Overcooked and starchy pasta, for example, digests much more swiftly than pasta served al dente.

The glycemic index scoring of some foods holds other surprises. Old-fashioned oatmeal with flattened grains of oats has a low GI (55), while instant or quick-cooking oatmeal, processed to make the grains thinner, has a higher rating (66) because we digest the thinner grains more quickly. Ice cream gets a low GI score (37) because its butterfat puts on the brakes, causing it to move through the digestive tract more slowly than low-fat sweets, such as jelly beans (78).

Thus the glycemic index is only one of a number of measures needed to identify healthful foods. We still must be mindful of calories and ingredients, such as saturated fat, that should be eaten in moderation. All fats and protein register zero on the glycemic index because they contain no carbohydrate. And some foods are so low in carbohydrate—salad vegetables, for example—that their GI ratings are meaningless.

Be prepared: we are about to hear much more about the glycemic index and a related term, glycemic load (which more realistically reflects typical portion sizes). Some of it will be Too Amazing to Be True! and some of it will be confusing and contradictory. In the end, however, the glycemic index will be one more useful tool for helping us compare carbohydrate foods to identify the better choices.

North Americans often snack on unhealthy foods that, rather than satisfy, tempt us to eat more. If nothing else, the glycemic index can help us choose carbohydrates that stay with us, suppressing between-meal hunger pangs and the consequences they bring. (For further information, see: www.glycemicindex.com and The American Journal of Clinical Nutrition, July 2002.)

Resources

Quick and Healthy Recipes and Menus
Overnight Oatmeal
Heart Healthy Diet Recipes and Menus
Diabetic Diet Center