DEAR DOCTOR K: I have Type 2 diabetes. Lately I've been hearing about low "glycemic index" and "glycemic load" foods being good for diabetics. What do these terms mean?
DEAR READER: Carbohydrates ("carbs," for short) are the major component of bread, pasta, cereals, fruit, milk, vegetables and beans. In your stomach and intestine, carbs are chopped up into sugars. Those sugars then are absorbed; they travel from the gut into the blood.
As a result, the carbs you eat -- and the KIND of carbs you eat -- have a strong impact on blood sugar levels. This is important for anyone with diabetes, or at risk for getting diabetes.
Different carbs impact your blood sugar differently. Carbohydrates are long strings of certain molecules. Think of them like a string of pearls. When they hit the gut, digestive enzymes start to chop them up. It is the one-pearl and two-pearl strings that are the sugars.
Different carbs are digested more or less easily than others. When carbs are easily chopped up into sugars, blood sugar levels rapidly rise to higher levels. When carbs are chopped up slowly, and only with difficulty, blood sugar levels rise slowly to relatively lower levels. This impact is measured in terms of glycemic index and glycemic load.
The glycemic INDEX indicates how easily a particular kind of carbohydrate is chopped up. Carbs that are easily digested and absorbed, and raise blood sugar levels rapidly, have a high glycemic index.
Of course, we don't eat pure carbs (except for table sugar). We eat foods that contain carbs, and some foods contain more carbs than others. The glycemic LOAD is based on the amount of carbohydrate in the food as well as its glycemic index value. So it gives a more accurate picture of a food's real-life impact on blood sugar.
For example, the glycemic index of a carrot is 131. In comparison, a serving of mashed potatoes has a glycemic index of only 104. However, a half-cup serving of carrots has only about 4 grams of carbohydrate. The same quantity of mashed potatoes has more than 18 grams of carbohydrate. That's why the glycemic load for a serving of carrots is 11, while that of a serving of potatoes is 20.
Even though it has not yet been proven by a scientific study, what we know about the human body convinces me that it is prudent to generally eat foods with a low glycemic load. I think there are likely to be health benefits, and there's surely no harm.
On my website (AskDoctorK.com) there is a table that gives the glycemic index and glycemic load of common foods. (Also on the site is a Special Health Report, "Healthy Eating for Type 2 Diabetes," that you can order online or by calling 877-649-9457 toll-free.)
In general, to follow a low glycemic diet, choose less-processed whole grains over refined grains; eat a lot of non-starchy vegetables, beans and fruits; and eliminate sugar-sweetened drinks.
Dr.Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.
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