Anne McNamara, DPM - Plymouth, NH

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Carbohydrates and The Glycemic Index: Quick, Slow, or Confusing

Once upon a time, carbohydrates were classified as sugars or starches. Today, carbs such as fruits, vegetables and grains are classified by their glycemic effect: that is, their ability to elevate blood sugar. The Glycemic Index (GI) ranks carbs according to their ability to elevate blood glucose. It was originally developed as a tool to help people with diabetes. Today, several popular diet books and magazines have expounded upon the virtues of avoiding carbs such as carrots, potatoes, and white bread because they have a high glycemic effect. Supposedly, they quickly elevate blood sugar, stimulate the body to secrete too much insulin, and this, in turn is said to promote fat storage.


Should I stop eating bagels and pasta? I've heard they are fattening because they quickly digest into sugar, which raises insulin and encourages fat storage. Is that true?


No. Sounds plausible, but the bottom line is: excessive calories promote fat storage, not excess insulin. If you lose weight after you stop eating bread or pasta, you do so because your are eating fewer calories, not because these foods are inherently fattening.

The Glycemic Index and Exercise

Exercise scientists, fascinated by the way different carbohydrates affect blood glucose, have explored the idea that low glycemic foods might enhance endurance performance by providing a slow release of glucose into the blood. One of the first studies to look at low glycemic pre-exercise foods reported that cyclists who ate (low glycemic) lentils before they exercised to exhaustion were able to pedal hard for 117 minutes, as compared to only 97 minutes when they ate (high glycemic) potatoes a significant difference!


Should I eat slowly digested carbohydrates like lentils before I exercise because they provide sustained energy? If I were to do so, I'd end up with intestinal distress.


The answer depends on the situation. Choosing foods based on GI is particularly important for endurance athletes who cannot take in fuel, such as sports drinks or gels, during exercise. But if you exercise for more than an hour and can consume energy while exercising, that is the best way to enhance endurance. Hence, you need not choke down lentils or bran cereal, thinking they will help you, when they actually might only create problems. If you cannot take in fuel during exercise, you may benefit from low glycemic pre-exercise carbs. Experiment during training.

High glycemic foods (sugary beverages, bagels, watermelon) are good recovery choices if you exercise hard more than once in a day (such as at a track meet or soccer tournament). High glycemic carbs can most rapidly refuel the glycogen stores depleted during the first exercise bout.

Note: If you are sensitive to sugar and easily experience sugar "lows", experiment with eating more low glycemic foods. You may be better off choosing (low glycemic) yogurt as compared to the same amount of calories of (high glycemic) rice cakes. Take heed and make wise food choices!

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