As of Saturday, May 11, 2013
DEAR DOCTOR K: Can you explain the importance of glycemic load, as opposed to glycemic index, when judging carbohydrates?
DEAR READER: Carbohydrates, along with proteins, fats, vitamins, minerals, water and oxygen, are nutrients: We need them to live and grow. But even though we need carbohydrates, there still are carbohydrate-rich foods that are “good carbs” and “bad carbs.”
Carbohydrates are the main nutrient in bread, pasta, cereals, beans, vegetables and dairy foods. All sugars are carbohydrates. When you eat, your body breaks carbohydrates down into sugar molecules. The smallest sugar molecule, glucose, is absorbed from your gut into your blood. It travels through the blood to every cell, providing an important source of energy to each cell.
Some foods are easily and rapidly digested into glucose. Such foods have a high glycemic index. With other foods, the process of digestion goes slower. These foods have a low glycemic index.
To give a cell energy, glucose has to get from the blood to the inside of the cell. That’s the job of insulin, a hormone made by the pancreas (a small gland in your abdomen). Insulin also travels in the blood, and when insulin attaches to a cell, it allows glucose to get inside it.
OK, those are the basics. When you digest carbohydrates, a certain amount of glucose will enter your blood. How much, and how rapidly, depends on two things: how much carbohydrate there is in the food, and the glycemic index of the food. Together, these two measures determine the glycemic load. If there are a lot of carbs in a food and the glycemic index of that food is high, then there will be a rapid, high spike of sugar in your blood: The glycemic load will be high.
When your blood levels of glucose rise, your pancreas senses this and promptly releases insulin. Foods with a high glycemic load cause your pancreas to suddenly work very hard to make and release insulin. In general, a lower and slower conversion from carbohydrate to blood sugar is better for your health. In other words, foods with a low glycemic load are better.
Here are some examples of foods with different glycemic loads:
— Low glycemic load (10 or lower): lentils and beans, fruits and vegetables, nuts and seeds, whole grains.
— Medium glycemic load (11 to 19): steel-cut oatmeal, whole-wheat pasta, some breads, fruit juices without extra sugar, brown rice, sweet potatoes.
— High glycemic load (20 or higher): Soda, energy drinks and other sugar-sweetened beverages, candy, white rice, French fries and baked potatoes, sugary breakfast cereals.
(I’ve put a table showing the glycemic index and glycemic load values of many commonly eaten foods on my website, AskDoctorK.com.)
Don’t misunderstand: I’m not saying it’s dangerous to eat foods with a high glycemic load. But your diet, on average, should favor carbohydrate-containing foods that have low glycemic loads.
Dr. Anthony L. 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.