The Limitations of the Glycemic Index

Our team of medical nutrition therapists at the Delaware Valley Institute of Fertility & Genetics (DVIF& G) in Marlton help patients make healthy lifestyle changes to prevent certain diseases, including obesity, type 2 diabetes and cardiovascular disease but primarily to treat infertility. Studies have shown that the role of diet and nutrition is very important not only in helping couples conceive, but also in helping them achieve a healthy pregnancy and birth. Recently, both the American College of Obstetricians and Gynecologists (ACOG) and the American Medical Association (AMA) have issued policy statements encouraging practicing OB/GYNs in particular, and primary care physicians (PCPs) in general, to address preconception health issues in women of reproductive age.

One of the tools that they may reference in nutrition counseling is the Glycemic Index (GI). The GI is a tool used to rank different types of carbohydrates, such as white rice, pasta, or cereal, according to their effect on blood sugar levels, also known as glucose levels. The higher the GI rating, the faster that carbohydrate turns to sugar in your blood. The lower the GI rating, the slower it turns to sugar in your blood. The body works to keep these levels in balance. Use of the GI can help achieve a glucose balance that’s right for a particular individual.

But there are limitations to using the GI as the primary guide to nutritional intake. It should be used as a reference tool, not as a strict list of foods that are allowed and foods that are forbidden. Because the GI is an average, the GI of a food can be highly individual. For example, just because a GI of a particular food is not supposed to raise blood sugar levels, that doesn’t mean that it won’t in certain individuals. 

It's also crucial to control portion size. Even though a certain carbohydrate may be on the lower half of the index, larger helpings of that food can still trigger excessive insulin surges and extra calories causing weight gain. The same applies for a high GI. If smaller portions are eaten, insulin surges and glucose levels are minimized. Also, when carbohydrates are eaten along with other foods, the blood glucose response and GI will vary, depending upon the amount of carbohydrate, protein, and fat in the mixed meal. 

A registered dietitian (RD) can help develop a personalized meal plan for an individual, one that achieves the optimum balance of carbohydrates, protein, fat, and vitamins and minerals. Instead of solely focusing on GI ratings, the RD helps the person control portion sizes, total carbohydrates, and fat intake to achieve a healthy weight. 

We have helped hundreds of women adopt a healthy lifestyle. Since nutritional adjustments require changes in well entrenched habits, this can be associated with additional stress that can undermine the effort in developing a  new healthy lifestyle. Therefore, low-impact exercise, eating right, and meditation, or other stress reduction techniques are included. The GI offers insight to registered dietitians in planning nutritious meals for their patients, but it’s only one of many reference tools used by us to create meal plans that deliver healthful benefits.  

By Karla D. Boyce, RD, LDN, CDE

Date Posted: August 2, 2006