Understanding the Glycemic Index

The glycemic index (GI) ranks car­bo­hy­drate foods by their effect on blood glu­cose lev­els. High GI foods like corn flakes and gra­ham crack­ers elicit a greater increase in blood glu­cose — mak­ing more energy avail­able to your mus­cles more quickly — than low GI foods such as apples, beans and yogurt. How­ever, con­tro­versy sur­rounds the use­ful­ness of the GI because the blood-sugar effect varies depend­ing on the amount of food eaten, how it’s pre­pared and each person’s indi­vid­ual response.

Despite its lim­i­ta­tions, nutri­tion­ist Gidus sug­gests that an ath­lete fine-tune her food intake with the GI. “I rec­om­mend eat­ing low-GI foods before exer­cise to pro­vide a more sus­tained energy release. Mod­er­ate– to high-GI foods are best dur­ing and post-exercise for imme­di­ate reple­tion of glyco­gen,” she says.

Before: apples, plums, cher­ries, peanut but­ter, milk, yogurt
Dur­ing: grapes, sports drinks and gels
After: bagels, pota­toes, juices, sports drinks and gels

The GI doesn’t tell it all, how­ever. It mea­sures the effect that 50 grams of carbs in a par­tic­u­lar food has on blood sugar, but it doesn’t fac­tor in the rel­a­tive amount of carbs in an aver­age serv­ing of that food.

That’s why some nutri­tion­ists use the glycemic load (GL) instead. Water­melon, for exam­ple, has a high-glycemic index because 50 grams of car­bo­hy­drate in the fruit has a large effect on blood sug­ars. But since a typ­i­cal slice con­tains only about 6 grams of carbs, watermelon’s GL and it’s effect on blood sugar is small. The same is true for car­rots. They have a high GI, but a low GL.

For more info and to find out GI/GL val­ues of cer­tain foods, search the GI Data­base on glycemicin​dex​.com. Exper­i­ment with dif­fer­ent pre– and post-exercise meals to learn your best strat­egy. The glu­cose response varies from per­son to per­son and even from meal to meal.

Excerpted from Carbs to Love on Active​.com