Low Glycemic Index Eating: The Science Behind the Numbers

What’s so great about the glycemic index?

It can help you understand the impact onyour blood glucose levels by how quicklyor how slowly your body digests thecarbohydrates you eat. But how can youknow the rate of digestion of a particularcarbohydrate food?

The glycemic index spells it all out for you.

Thanks to dedicated scientists in severalcountries throughout the world, a specificprotocol is followed in research laboratoriesto test the rate of digestion of certaincarbohydrate foods.

Here’s what they do:

1. Eight to 10 volunteers are chosen toparticipate for each food to be tested. Theyare instructed to arrive at the research lab ina fasting state. Their fasting blood glucoselevels are measured.

2. They are then given a specific amount ofthe test food. The actual amount varies fromfood to food, but it must be equivalent toeither 25 or 50 grams of carbohydrate.

3. The volunteers’ blood glucose levels aremeasured and recorded every 15 minutesduring the first hour and every 30 minutesduring the second hour. (If the volunteer hasdiabetes, blood samples are measured over aperiod of three hours.)

4. All recorded values are plotted on a graph,and the area under the resulting curveis calculated by a specialized computerprogram.

5. The volunteers’ responses to the testfood are compared with their responses tothe reference food (either white bread orglucose), which were previously measuredand recorded in exactly the same way. Infact, these responses are tested two or threetimes on different days and an average iscalculated. This average value minimizesthe effect of day-to-day variations in thevolunteers’ blood glucose responses.

6. Once all the values of all the volunteersare averaged, the glycemic index (GI) valueof that food is established and added to thelist. At present, more than 600 carbohydratefoods have been tested this way.

The glycemic index attests only to the qualityof a carbohydrate based on the time it takesfor its digestion. Foods with a high GI value(known as “gushers”) are digested morerapidly into glucose, causing a rapid rise inthe blood glucose level. Those foods with alow GI value (“tricklers”) are digested moreslowly, resulting in a smaller, more sustainedexcursion of glucose into the bloodstream.

But, as we know all too well, how muchcarbohydrate one eats also affectsone’s glycemic control. You’ve probablyexperimented with how much pumpkin pieor mashed potatoes you can “get away with”on Thanksgiving Day. By keeping your eyeon portion sizes, you are addressing your“glycemic load,” that is, the actual amountof glucose that enters your blood aftereating a particular amount of a particularcarbohydrate.

A nice perk of using the glycemic indexis that if you are a “volume” person, wholikes to eat large portions, knowing whichfoods enter the bloodstream slowly givesyou an edge. Choosing your foods carefullywith help from the glycemic index willhelp you maintain more controlled bloodglucose levels. But a word to the wise: Don’tgo overboard, because the calories thataccompany those low GI carbs add up, andwhen they are too many, they’re too many,no matter how healthy your food choice.

The Glycemic Index rankscarbohydrate foods on ascale of 0 to 100 based ontheir impact on BG levelsafter consumption. Thehigher the glycemic index,the more rapid the spike inBG levels.

Low: 0 to 55
Peanut butter 14
Pasta 44
Baked beans, canned 48
Intermediate: 56 to 69
Raisins 56
Instant oatmeal 66
Pancakes 67
High: 70 or more
Bagel 72
Cheerios 74
Pretzels 83
Cornflakes 92