Glycemic index 101

If you live with diabetes, you’re probably familiar with the glycemic index (GI), a tool that can help people understand and manage blood sugar. But experts say the GI has elements all of us may find useful when it comes to understanding how our bodies process carbohydrates and regulate energy.

WellTuned talked with Reena Panjwani, registered dietitian-nutritionist at BlueCross BlueShield of Tennessee, to find out more.

What is the glycemic index?

“The glycemic index is a system that assigns values to foods that contain carbohydrates. The higher the value, the more you can expect that food to increase your blood sugar,” says Panjwani. “The index only scores foods containing carbohydrates, or carbs, which is why it’s most often used by people who have diabetes.”

Carbs are a nutrient that takes the form of sugar, starch and fiber. When you eat or drink a food that contains carbs:

  • Your body breaks down sugar and starch into glucose, the main source of your body’s energy, while
  • Fiber travels through your body undigested.

How does the glycemic index affect energy levels?

The GI measures how much a food is likely to raise blood glucose levels.

  • Foods lower on the GI have a slower absorption rate, which means they may give you sustained energy.
  • Foods higher on the GI are more likely to give you energy short-term, but that energy may run out quickly.

However, it’s important to note that everyone’s body breaks down glucose differently, so the GI is a guideline, not a hard-and-fast rule. Low GI foods may foster weight loss, while higher GI foods may help you recover energy faster after exercise.

How does the glycemic index break down foods?

GI values are divided into 3 categories:

  • Low GI: 1-55
  • Medium GI: 56-69
  • High GI: 70+

For example, a white potato has a high GI value of 77, while a sweet potato has a medium GI value of 63.

“Generally speaking, foods that are lower on the GI are often higher in fiber, and higher GI foods tend to be more processed,” says Panjwani. “That’s one reason eating whole wheat bread instead of white is a better choice.“

What should people consider before testing the glycemic index for themselves?

“The GI is just one tool people can use to manage blood sugar, but there are a few caveats to consider,” says Panjwani. “For example, the GI:

  • Does not account for portion size
  • Only looks at foods individually — aka ‘cooked macaroni’ versus ‘macaroni and cheese’ — and most of us don’t eat foods plain, and it
  • Can be significantly affected by ripeness and cooking method.

“A ripe banana may increase your blood sugar more than a less ripe one because more of its starch has converted to sugar,” Panjwani says. “Cooking also makes a difference. If you eat a whole boiled potato, it will have a lower GI (78) than a mashed potato (87), simply because of the way the sugars and starch in the food change with cooking. In fact, if you overcook pasta, its GI value goes up.”

It’s also important not to look at foods in a vacuum. Chocolate, for example, is a low GI food while oatmeal has a higher value. That doesn’t mean you should eat chocolate for breakfast everyday, says Panjwani. Instead, you might consider opting for dark chocolate as a sweet treat over something with a higher GI, like sugary cereal.

“Just because something is high GI doesn’t mean it’s not healthy,” says Panjwani. “Foods like fruits (pineapple, watermelon) have other nutrients. So while you may experience short bursts of energy if you eat only pineapple, having it as part of a balanced meal likely won’t affect your blood sugar the same way.”

Here are how some common foods rank on the glycemic index:

  • Low GI: Green vegetables, some fruit, raw carrots, beans, lentils, nuts, low-fat dairy
  • Medium GI: Corn, bananas, raw pineapple, oat breakfast cereals, multigrain bread
  • High GI: Cake, doughnuts, croissants, and white rice, bread and potatoes

Click here to explore the glycemic index of 60+ foods.

BlueCross BlueShield of Tennessee members can access wellness-related discounts on fitness products, gym memberships, healthy eating and more through Blue365®. BCBST members can also use tools and resources to help improve health and well-being by logging into BlueAccess and going to the in the Member Wellness Center under the Managing Your Health tab.

Ashley Brantley

Ashley Brantley

Ashley Brantley has been writing about food, culture and health for more than a decade, and has lived in three of Tennessee’s four major cities (Memphis, Nashville and Knoxville).

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BlueCross BlueShield of Tennessee members can access wellness-related discounts on fitness products, gym memberships, healthy eating and more through Blue365®. BCBST members can also use tools and resources to help improve health and well-being by logging into BlueAccess and going to the in the Member Wellness Center under the Managing Your Health tab.