HealthNotes

• By Suzanne Dixon, MPH, MS, RD

Type 2 Diabetes Risk: Carb Quality Counts

Among people with a family history of type 2 diabetes, genetics plays a role in disease risk, but poor diet, lack of exercise, and obesity are far more important for tipping the balance toward developing the disease. And once you have diabetes, heart disease, blindness, kidney disease, nervous system damage, and other complications also become a risk. So it’s important to pinpoint which of our choices can best keep diabetes at bay.

Eating more dietary fiber significantly decreases the risk of developing type 2 diabetes

Proof of principle

Glycemic index and glycemic load are measures of how carbohydrates affect our blood sugar levels. Glycemic index refers to how quickly 50 grams of carbohydrate from a food will raise blood sugar levels and how high those levels will go. The higher the glycemic index, the higher the blood sugar and the more quickly it will rise. But glycemic index doesn’t account for the carbohydrate content in a typical serving size, which is where glycemic load comes in.

Health experts have long suspected that glycemic index and glycemic load are related to type 2 diabetes risk and now they have added ammunition that this connection is real.

To study carbohydrate quality and diabetes risk, researchers collected diet information from 37,846 healthy, diabetes-free 21- to 70-year-old adults. After following the group for 10 years, the researchers found:

• A higher glycemic load diet significantly increases risk of developing type 2 diabetes.
• A higher glycemic index diet increases the risk of developing type 2 diabetes, though not as much as a higher glycemic load diet.
• Eating more dietary fiber significantly decreases the risk of developing type 2 diabetes.
• Eating more starch increases the risk of developing type 2 diabetes.

You don’t have to count carbs to make your carbs count

Exhaustive glycemic index lists are available, but as this study shows, glycemic load may be the more important number. The glycemic index for carrots is 131. For white pasta it’s 71. But a serving of carrots contains 4 grams of carbohydrate vs. the 40 grams found in a 1-cup serving of pasta. You’d have to eat several pounds of carrots to get 40 grams of carbohydrates!

The glycemic load, which adjusts for the carbohydrate content in a serving size, tells the true story. Carrots have a glycemic load of 5. Pasta’s glycemic load is quite high at 28.

To avoid driving yourself crazy with glycemic index lists, consider the three things that lower the overall glycemic load of the diet: protein, fat, and fiber. This is one reason why the glycemic load of carrots is so low. The carrot fiber blunts the blood sugar effects of carrot carbohydrates. And, of course, the total amount of carbohydrate in a serving of carrots is low. This also partly explains why whole foods, like oranges, are a better nutrition choice than, say, orange juice, which offers minimal fiber.

Focus on getting protein, healthy fat, and fiber into all of your snacks and meals. For a snack think apple and peanut butter rather than apple juice and crackers. Ditch the processed foods and white (enriched) flour snacks. Focus on food that looks like, well, food!

And finally, don’t forget about your waistline. Overweight and obesity, which affect close to 70% of adults in the US, are leading risk factors for type 2 diabetes. 

(Am J Clin Nutr 2010;92:905–11)