The Glycemic Index: Who Needs It & Why You Probably Don’t

Tuesday, September 26, 2006 - 2:30pm

By Katie Clark, MPH, RD

Should people who are watching their weight worry about the glycemic index (GI) of carbohydrate foods? Well, unless you have diabetes, the answer is no. In recent years, the glycemic index and glycemic load concepts have received unwarranted attention as mystical, magical components of weight management. This in-depth analysis can help you understand why you shouldn’t waste your time worrying about them.

What is the Glycemic Index?

The glycemic index is a ranking system that determines a food’s ability to raise your blood glucose. High blood sugar levels in people with diabetes are linked to a higher number of poor health outcomes and premature deaths than in people with better blood sugar control.

How glycemic load is calculated

All foods on the glycemic index are compared to a standard, such as pure glucose or white bread (those two foods score 100). The glycemic index multiplied by the amount of carbohydrate in a food determines its glycemic load. A food with a high glycemic load will raise your blood sugar more quickly than a food with a low glycemic load.

Pitfalls of the Glycemic Index

If you do not have diabetes, the glycemic index tends to be an unhelpful and unnecessary concept for most dieters. Focusing on the amount of time it takes for a food to raise your blood sugar overshadows the most important concept in weight-loss: Your weight is ultimately controlled by the amount of calories you consume versus the amount of calories you expend.

One shortcoming of the glycemic index is its weight-based test measurement system. A 50-gram sample of a food is used to determine its glycemic load. If you take 50 grams of apple, it ranks in the middle of the glycemic index, meaning it has a moderate effect on elevating blood glucose. Fifty grams of a baked potato is near the top of the index, it quickly raises your blood glucose. But 50 grams of potato contains almost twice as many calories as 50 grams of apples1 . When you look at more realistic serving sizes, the glycemic load of an apple is actually much lower per serving size than are potatoes.

Other limitations include factors that can alter glycemic index test results, such as a person’s height, weight, body type, hydration status or even the time of day2. Different foods consumed at a meal can also affect another food’s ability to raise blood sugar. There is evidence that even a cup of coffee can change glucose uptake time3.

Potentially useful applications of the Glycemic Index

Most whole grain complex carbohydrates tend to have lower glycemic loads than refined, white-flour foods. But consumers should be concerned about eating low glycemic load foods for their nutritional value and fiber content, not for their role on blood sugar levels.

An exception exists for a person with diabetes. A diabetic person must be concerned about the daily fluctuations in his or her blood glucose. In the case of diabetes, the glycemic index can be a helpful learning tool for selecting carbohydrate-containing foods. For the remainder of the population, blood sugar levels are much less important than the calorie content and nutrient content of a food. There is no conclusive evidence showing that blood sugar levels in non-diabetics play a major role on a person’s weight.

Conclusion: Glycemic Index is important for diabetes management, rather than weight loss

Emerging research does occasionally link glycemic load with various weight loss outcomes4. However, if you do not have diabetes, you should be cautious of overemphasizing the effect of a food’s ability to raise your blood sugar in a specified period of time.

At the end of the day, your ability to gain, lose or maintain weight is determined by the number of calories you ingest and expend. Glycemic load is a feasible concept if you are concerned about blood sugar levels for diabetes management. For the rest of us, it is more important to address the calorie and nutrient content when choosing carbohydrate foods.

1 USDA Agricultural Research Service, Nutrient Data Laboratory. Available at:
2 A. Baylin and coauthors, Adipose tissue biomarkers of fatty acid intake, American Journal of Clinical Nutrition 76 (2002): 750-757.
4 G. H. Anders, D. Woodend, Effect of glycemic carbohydrates on short-term satiety and food intake, Nutrition Reviews 61 (2003): S17-S26.