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Using the Glycemic Index to Choose Carbs
Q: What the heck is all the hoopla over the Glycemic Index (GI) of food? Can you explain to me why peanut M&M's are lower GI than rice cakes, and what this really tells me? How in the world can I incorporate yet another confusing piece of information into making appropriate food choices?
A: Now before all of you go running to the store to stock up on peanut M&M's, here's a little background. First of all, each of us (not just diabetics) could benefit from an understanding of the Glycemic Index of food, which measures how quickly carbohydrates/sugars are converted to blood sugar (or glucose.) Glucose itself is set as the standard, and rated at 100 (although there's another scale that uses white bread as the standard at 100-check your chart to see what is what). All other carbohydrates are then rated in relationship to glucose. Foods high in GI release glucose very quickly, resulting in an energy spike that sustains you for mere minutes. Foods low in GI release glucose more slowly, resulting in more sustained energy over several hours.
In other words, carbohydrates are NOT equal. The GI rating also does NOT entirely depend merely on whether a food is a simple or complex carbohydrate. Factors that affect the GI include: 1) quantity of fiber (the more fibrous, the longer it takes to digest and absorb, the lower the GI); 2) how easily the food is actually digested (anything with protein or fat takes longer to digest, hence lowering the total GI of what you're eating); 3) quantity of specific sugars (fructose converts slowly, maltose more quickly), and 4) the form in which the food is eaten. Cooking or pre-cooking can also raise the GI--quick cooking oatmeal is much higher than slow-cooked oatmeal. Liquids are more quickly assimilated by the body, hence one of the values of consuming a post-workout drink immediately after a hard workout ,when you want to replenish muscle glycogen as quickly as possible.
Combining and Timing
How, then, can you properly incorporate the higher GI foods such as bananas, bagels, potatoes, carrots, raisins, bread, rice, cereals, and so on that most of us have grown to love so much? COMBINING and TIMING. By combining a high GI food with protein, fat, or low GI carbs, you reduce the overall GI rating, resulting in satiation over a longer period of time. Result? Less consumed over time, and, ultimately, weight loss! Go ahead and add a bit of cream cheese or peanut butter to that bagel. Have some yogurt with the cereal. Have a small amount of butter on the bread, or better yet, make it a turkey or tuna sandwich.
Furthermore, the BEST time to eat those high GI foods is immediately following any strenuous workout when the muscles are depleted of glycogen. That's why it's so common to see bananas and bagels at the finish lines of marathons, triathlons, and other endurance events. However, make sure that the meal preceding your endurance workouts is full of lower GI foods so that you can prevent "bonking" or "hitting the wall."
Carb Craving Cycle
Now you may begin to see how craving carbohydrates can result in weight gain: whenever glucose enters the bloodstream, insulin is secreted, delivering glucose to the cells for energy use OR storage as body fat. Sometimes the body overreacts in the presence of a sudden surge of glucose (as happens when you skip meals and have high GI foods on an empty stomach) and produces too much insulin, which then increases the tendency to store fat and also LOWERS your blood sugar levels, creating a vicious cycle of carb craving.
As for the initial question above, regarding rice cakes (rated 110) vs. peanut M&M's (chocolate, rated 70, combined with peanuts, rated 21, which makes the total GI about 55) if you compare calorie for calorie, the peanut-containing M&M's will leave you feeling a lot more satisfied than puffed rice, and not merely because of the flavor and texture. That may indeed mean stopping at just 6 peanut M&M's as opposed to 3 whole rice cakes or 6 carrots, but have you noticed how hungry you still feel after having those carrots or rice cakes?? So much for calling them "diet foods"--they may as well be "anti-diet foods!"
Here is a sample of popular carbohydrates and where they rate. For a much more complete listing, visit Rick Mendosa's Glycemic Index of foods. These are compared with white bread, given a rating of 100.