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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. Question
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? Answer 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! Question 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. Answer
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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