Carbohydrates and glycemic load

Some people with diabetes use the carbohydrate counting method developed by the ADA to help manage their diabetes. Another way to capture how carbohydrate-containing foods affect blood sugar levels is a measure called glycemic load.

You may already be familiar with glycemic index (GI), which is a measure of how 50 grams of carbohydrates from a specific food affect blood sugar levels. For this measure, the amount of food consumed is the amount that will provide 50 grams of carbohydrates. The resulting glucose response is compared against a standard—typically a glucose drink, table sugar, or white bread. GI is useful, but can be misleading because it doesn’t account for typical serving sizes that a person may eat.

Glycemic load (GL) takes GI one step further, by taking into account the amount of carbohydrates in a typical serving. For example, 50 grams of carbohydrates from carrots have a strong effect on blood glucose levels, so carrots have a high glycemic index. However, carrots are mostly water and fiber, so when eaten in typical quantities of a carrot or two at a time, they provide much less than 50 grams of carbohydrates, and therefore have little effect on blood sugar levels. Because an individual carrot’s carbohydrate content is small, it has a low glycemic load.

What is the evidence?

In 2013, one of the largest studies to examine the effects of glycemic load on health was published. The study was a meta-analysis of 24 studies, meaning researchers combined and analyzed the data from 24 studies to determine if there was a relationship between daily glycemic load and diabetes risk. To adjust for the person-to-person differences in calorie intake, the glycemic load (calculated in grams) was standardized to a 2,000 calorie diet of the same composition as the original diet. This way, the glycemic load of the diet of a 120 pound woman could be compared with the glycemic load of the diet typically consumed by a 250 pound man.

The meta-analysis from 2013 found that the protective effect of a lower GL diet was stronger in women than in men, and found that for every 100-gram decrease in daily glycemic load, the risk of developing diabetes dropped by 45%. This is great news for those 86 million Americans living with prediabetes: paying more attention to the glycemic load of your diet may pay off in terms of a lower risk of diabetes.

Diabetes risk vs. diabetes management

What about GL and GI for people who already have diabetes? In a 2008 comprehensive review and meta-analysis of the research on this topic, the authors noted, “The best evidence of the clinical usefulness of GI is available in diabetic patients in whom low-GI foods have consistently shown beneficial effects on blood glucose control in both the short-term and the long-term.” In other words, for people who already have diabetes, using glycemic index is effective for managing blood sugar levels. The meta-analysis focused on GI, not on GL; however, given that GL is considered an even better measure of how carbohydrate-rich foods affect blood glucose, the authors concluded that, “GI and GL are to be considered among the parameters to be used for selecting appropriate foods for the diet of people with diabetes or impaired glucose regulation.”

Reduce your daily glycemic load

If you have diabetes, do not change your diet without talking to your doctor or dietitian first. Your healthcare provider can determine if focusing on GL to manage your diabetes is appropriate for you. If you are interested in learning more about GL, ask your doctor for a referral to a dietitian or a certified diabetes educator (CDE), and that person can help you work the GL approach into your diabetes management plan.

If you don’t already have diabetes, there are some easy steps you can take to lower the glycemic load of your diet, which may reduce your risk of type 2 diabetes:

• Focus on fruits and vegetables with a high water content. Starchy fruits and vegetables like bananas and potatoes have higher glycemic loads. Dried fruits (including raisins) and fruit juices also have higher glycemic loads. Eat these foods in moderation and focus on foods with a high water content such as melons, citrus, and stone fruit, like peaches and plums.
• Use whole grains. Choose brown rice over white rice and whole or steel cut oats over instant rolled oats. Pasta (one cup or less) and bagels (one-half of a bagel or a bagel thin) should be limited—they have especially high glycemic loads because they are carbohydrate-dense. When considering whole grains, keep in mind that wheat is a common allergen, so go for other options, such as gluten-free whole grains like quinoa, brown rice, amaranth, and millet, if you are allergic to wheat.
• Snack on nuts. Nuts and seeds are low in carbohydrates and therefore have very low glycemic loads. They also provide healthy fats that are beneficial for everyone, although portion sizes of nuts should be limited to one ounce (about 1/4 cup) because they are calorie dense. Because tree nuts and peanuts are considered common allergens, be sure to avoid them if you are allergic to them.
• Use reputable resources. For more information on the GI and GL of a variety of foods, try the Harvard Health Publications Glycemic index and glycemic load for 100+ foods chart: http://www.health.harvard.edu/healthy-eating/glycemic_index_and_glycemic_load_for_100_foods.

With a few positive dietary changes, we all can promote the ADA's goal of “a life free of diabetes and all of its burdens.”

(Am J Clin Nutr 2008;87:269S–74S.)