What the Glycemic Index really is

Maybe you’ve heard of it? The Glycemic Index (The GI) originally was created as a guide for people with Diabetes to help control blood sugar. Along the way, scientists discovered that the GI might also help people lose weight. Several diet plans use the GI as the basis of their approach – such as The Zone Diet, Sugar Busters and the Paleo Diet.
The foundation of the GI is a food rating system. Foods were given a score, based upon how much they caused blood sugar to rise after being eaten. Why? When blood sugar rises, the body matches it with a release of insulin to tuck the sugar away into the cells for energy. When there is excess blood sugar, the insulin will change the extra into fat.
To help guide people into choosing food to meet energy needs, but to avoid adding fat pounds, scientists studied carbohydrates more closely. All foods were ranked and put into a chart. The foods fell into categories of high (over 70), medium (56-69) and low (under 55) GI foods. High GI foods are chock full of sugar and starch, while low GI foods tend to be higher in fiber. Most people simply look at high and low GI foods. Also, there are foods with few or no carbs (most vegetables, fats, meat, fish and poultry), which have such a low GI that they’re not even rated. The premise of the rating system is to encourage people to load up their plates with low GI foods most of the time. The result should be better blood sugar control and weight loss.
Unfortunately, it’s not that simple. Just because an individual food, in a lab, got a specific GI score, it may vary widely in the real world. The actual GI of a food can change significantly, depending upon:
• Ripeness of fruits & vegetables
• Storage time
• Food preparation and cooking method
• Combination of foods served during a meal (for example, a casserole with fiber, fat and protein can lower GI)
• Individual body chemistry- not everyone responds the same to food; age and exercise also affect the GI
There are other downsides. Just because a food is rated as high GI, it doesn’t mean that it is unhealthy. High GI foods can be good sources of nutrients (e.g. whole wheat bread, sweet potatoes). And just because a food is rated as low GI, it does not mean that it is an ideal food to eat nor does it mean you can eat endless amounts of it. Potato Chips and chocolate bars happen to both have a low GI, but that doesn’t mean they are healthy. Although they don’t cause a big rise of blood sugar, they are high in fat, sodium and calories; meaning in small amounts chips and candy bars can be quite unhealthy and work against you. Finally, portion size still matters when it comes to healthy eating, but that is not mentioned at all in the Glycemic Index.
So, the big question is this- does the GI rating of a food matter when it comes to weight loss and blood sugar control? The answer is yes, to a degree; meaning use that information as part of a plan not the basis of your eating style. In general, it is best to choose foods with a lower GI if they are those with a high fiber level such as whole grains, peas, beans, vegetables and fruit. Additionally, add to your plan other healthy foods such as lean meats, poultry, fish, nuts, seeds, and low-fat dairy. Portion control plays a vital role, one in which you need to be vigilant. Remember that despite choosing a low GI food, if you eat tons of it, the calories will add up. Also, keep in mind that it is okay to occasionally have those high GI foods as treats.
You can find out more about the specific GI of a food in the chart below; although a more detailed chart is found at Another, more personalized approach is to meet with a registered dietitian. The benefit of a nutrition consult with a dietitian is that a highly personalized eating plan can be developed specifically for you based upon your unique needs.
The Glycemic Index*
A comparison of some common foods
Higher GI
White Bread 71
White Rice 75
Baked White Potato 85
Corn Flakes 93
Cous cous 65
Popcorn 72
Mashed Potato 87
Orange Juice 57
Banana 51
Grapes 59
Fruit Roll Up 99
Lower GI
Whole Wheat Bread 51
Brown Rice 50
Baked Sweet Potato 54
All bran 55
Quinoa 53
Peanuts 14
Carrot 35
Orange 40
Grapefruit 25
Pear 38
Peach 42
* adapted from Harvard health Publications,, and The Mayo Clinic
Jennifer Giffune, R.D., L.D.N. is a freelance author, professional speaker and nutrition counselor. On the last Wednesday of each month, Jennifer can be heard on 89.5 WSKB radio on the “Wake up Wednesday Morning” Show. To make an appointment with Jennifer at Mercy Medical Group, call 786-1500. Jennifer has offices in Feeding Hills and Springfield.

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