The Glycemic Index

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(Host) ‘Tis the season for rich food – and lots of it. Commentator Rachel Johnson says that understanding the glycemic index may help you eat better during the holidays.

(Johnson) There are times when I feel that I need to duck when the subject of glycemic index comes up with my colleagues. The index, also referred to as GI, is a system of ranking foods according to how much they raise blood sugar. It was first developed as a tool to help people with diabetes control their blood sugar. Now, it’s squarely in the public mainstream. Low-GI diet books crowd bookstore shelves, many diet plans have low-glycemic variations, and Australian supermarkets have food labeled with their GI ratings. But a huge debate about the value of the GI is raging in the nutrition community. Some of my colleagues are staking their careers on the GI’s importance, while others disparage its value. I’ve seen their arguments come close to blows. So – what makes the index so controversial? And until the dust settles, its there anything you can apply to your own eating?

First, a little background. The glycemic index measures how much a food raises your blood-sugar level compared to a pure sugar like glucose. Foods with a high GI value tend to cause a higher spike in blood sugar – and in insulin, the hormone that helps glucose get into cells. The spikes are especially problematic for people with diabetes, who lack an effective insulin system to clear sugar from their blood. And, because high-GI foods are quickly metabolized, they tend to make you hungry again more quickly than low-GI foods. David Ludwig, a Harvard physician and an advocate of low GI eating, found that obese teenage boys were hungrier after they’d eaten a high-GI breakfast of instant oatmeal, as compared with when they ate a low-GI breakfast of steel-cut oats or omelets. After a high-GI breakfast, they also ate 600 to 700 calories more at lunchtime.

Experts in the anti-GI camp poke holes in the concept. They argue that a low GI score is no guarantee of healthy fare. For example, cola, potato chips and some candies qualify as low or moderate GI foods. And the anti-folks point out that the biggest problem is that the GI looks at single foods, when the real issue is what happens with meals. For example, a high-GI potato becomes a low-GI meal if you add a pat of butter. This happens because the added fat helps slow the absorption of the potato’s carbohydrates. Some dietitians think these complexities are too confusing to make the GI useful for most people. Dr.Ludwig responded to this criticism by saying – quote – "Tell that to the thousands of people who come to our clinics!"

I told you the arguments can get heated.

Will the GI debate end any time soon? Knowing nutrition scientists as well as I do, I don’t think so. But in the end, choosing low-GI foods is common sense; for the most part they’re more natural, whole, unpolished and unprocessed. Getting more of these types of foods is smart eating, no matter which side you’re on.

Nutritionist Rachel Johnson is Dean of the College of Agriculture and Life Sciences at UVM and an advisor to EatingWell magazine.

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