What is the glycemic index?

How insulin works in your body

Insulin is a hormone that is produced by your pancreas. When you eat foods with carbohydrates, your body breaks down the sugar, or glucose. Insulin moves that glucose from your blood into your cells. Then, that glucose is used to produce energy in your body.

When you eat high-GI foods, your body digests them quickly, causing spikes to your blood sugar. This triggers your pancreas to release more insulin to use or store the glucose.

However, if you’re insulin-resistant, your body’s cells don’t respond to insulin effectively. So, even when your body makes more insulin, your blood sugar stays higher. Over time, this can lead to conditions such as Type 2 diabetes or metabolic syndrome.   

What is a healthy glycemic index?

In general, the lower a food’s glycemic index, the better it is for managing blood sugar.

Normal blood sugar levels are generally considered to be:

• Less than 100 mg/dL when fasting and less than 140 mg/dL two hours after eating for most adults without diabetes
• 80 to 130 mg/dL when fasting and less than 180 mg/dL two hours after eating for most non-pregnant adults with diabetes

“I advise my patients with diabetes to try to keep most of their foods in the low- to medium-GI range and save the high-GI foods as a special treat every once in a while,” Kikani says.  

Is the glycemic index a good tool to help manage blood sugar?

The glycemic index can be a useful tool to help you make healthy food choices. People with diabetes may also find it useful to better understand how certain foods impact their blood sugar.

“I use the glycemic index to counsel patients at UT MD Anderson on how to think about the foods they eat,” says Kikani. “Understanding how foods affect their blood sugar can help them build a diet that is nutritious and beneficial for their long-term health.”

Many people with diabetes also use continuous glucose monitors, which provide real-time feedback on how foods affect their blood sugar.

“With a continuous glucose monitor, whatever you eat, you can see the effect on your blood sugar almost immediately,” she says. “You can see what spikes your blood sugar, so you can choose to avoid or limit those foods.”

What is a low-glycemic diet?

A low-glycemic diet is made up of mostly foods with a GI score from 1 to 55. These foods are slower to digest, which helps stabilize blood sugar levels.

A low GI diet may include the following foods:

• Leafy greens: spinach, kale and lettuce
• Whole grains: oats, brown rice and quinoa
• Beans: lentils, black beans and chickpeas
• Nuts: almonds, walnuts, cashews and pecans
• Seeds: chia, pumpkin, flax, sunflower and hemp
• Berries: blackberries, blueberries, raspberries and strawberries
• Dairy: cottage cheese, plain yogurt, milk

What are the benefits of a low-glycemic diet?

A low-GI diet may help you:

• Lose weight or maintain a healthy weight
• Lower your risk for Type 2 diabetes
• Stabilize your blood sugar levels as part of long-term diabetes management

What are the worst glycemic foods?

Try to avoid sugary products like soda, sweetened fruit juices and desserts. These tend to have medium- or high-GI scores and can raise your blood sugar quickly.

“One can of soda has more added sugar than you and I need in an entire day,” says Kikani. “If you absolutely must have soda, diet soda is a better choice from a glycemic standpoint. But water is still the best option.”

Are there limitations to the glycemic index?

Absolutely. The glycemic index is not foolproof, says Kikani. Here are some reasons why:

Portion sizes

The glycemic index measures how quickly a food can raise your blood sugar. But it doesn’t account for how much you eat.

For example, blueberries have a lower glycemic index than pineapples. But if you eat two pieces of pineapple and two cups of blueberries, the blueberries will have a higher glycemic index, simply based on your portion size.

What is glycemic load (GL)?

Glycemic load (GL) is a measurement that combines the glycemic index with the amount of carbohydrates consumed in an actual serving. Glycemic load may be more helpful than using glycemic index alone in making food choices because it accounts for portion size. GL provides a more realistic estimate of how certain foods will impact your blood sugar.

GL is calculated by multiplying a food’s GI score by the number of carbohydrates (in grams) per serving. That number is then divided by 100.

Glycemic load ranges per serving are:

• Low GL: 10 or less
• Medium GL: 11-19
• High GI: 20 or more

A low-GI diet is one that has a total daily glycemic load of 100 or less.

How the food is cooked

Cooking methods can affect a food’s GI score.

For example, pasta cooked al dente, or firm, generally has a lower GI score than pasta that is cooked until very soft.

How the food is processed

Foods often have a higher GI score after they’re processed because processing can make carbohydrates easier to digest.

For example:

• Steel-cut oats have a lower GI than instant oats.
• Whole corn kernels have a lower GI than many corn-based breakfast cereals.  

Ripeness

Very ripe fruit tends to have a higher GI score than underripe fruit. This is because fruits that store starch while they’re developing convert a lot of that starch into sugar as they ripen.

Take bananas, for instance. An unripe (green) banana has more starch, which makes it firm and less sweet. As it ripens, that starch is converted into sugar. So, a ripe banana is softer and sweeter.

Low GI does not always mean healthy

The glycemic index only measures carbohydrates. It doesn’t account for overall nutritional value. Your body needs different vitamins and nutrients to stay healthy. So, building a healthy diet based only on the glycemic index isn’t ideal.

“A low glycemic index score does not automatically mean a food is healthy,” says Kikani.

Take butter, for example. It has a GI score of 0 because it has no carbohydrates, but it is high in saturated fat.

“Butter may not raise your blood sugar, but regularly eating large amounts may increase your risk for heart attack or other heart disease,” she says.

The opposite can also be true. A plain baked potato has a high glycemic index. But it also contains fiber and key nutrients like potassium, vitamin C and vitamin B6.    

Bottom line: Focus on overall nutrition

The glycemic index can be a valuable tool to help you understand how foods affect your blood sugar. But it shouldn’t be the only factor guiding your food choices.

The healthiest approach is a balanced diet rich in vegetables, fruits, whole grains, beans, nuts and seeds, while limiting highly processed foods and added sugars.

A nutritious diet can help you maintain a healthy weight, lower your risk for diseases and support overall well-being.

For cancer prevention, aim to fill at least two-thirds of your plate with vegetables, whole grains, fruits, beans, nuts or seeds. The remaining third can include meat, fish or animal products like cheese and eggs, or plant-based proteins like tofu.

Request an appointment at UT MD Anderson online or call 1-877-632-6789.