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Diabetes Prevention and the Low-Glycemic Index Eating Plan

How foods with a low glycemic index can prevent and help manage diabetes

With Mary Vouyiouklis Kellis MD

Low glycemic breakfast of eggs, avocado and salmon

What is the glycemic index?

The term glycemic index refers to a scale that ranks foods and beverages based on how each affects blood sugar (glucose) when it is measured two hours after eating. It categorizes foods and drinks on their ability to raise glucose levels (blood sugar) when you eat or drink each one on an empty stomach. Unfortunately, there is no one standard glycemic index database. Each presents a different set of numbers for various foods and beverages. The most prevalent scale sets the GI values from zero to 100, with zero indicating the food has no sugar and 100 as pure glucose, which would cause the greatest increase in blood sugar. Foods or beverages that have a GI below 55 are considered to have a low GI, while those 55 to 69 have a moderate GI and those 70 and above have a high GI.

What foods have a high, low or medium GI?

Despite the subtle variations in different types of GI scales, they are all in agreement on which foods have a high GI index. Refined grains and foods that contain a lot of sugar have a high GI, while high-fiber foods such as many vegetables, beans and whole grains as well as many fruits have a low to moderate GI.

Low glycemic foods include:

  • Fruit
  • Vegetables
  • Nuts and legumes
  • Milk and other dairy
  • Beans and lentils
  • Seafood, poultry and meat

Foods with a moderate GI include:

  • Whole wheat and rye bread
  • Brown rice
  • Whole grains and oats
  • Sweet potatoes
  • Corn

High glycemic foods include:

  • White rice
  • White bread and other baked goods made with white flour
  • Sugar-sweetened cereals
  • Pizza
  • Pasta

What occurs in your body when you consume a high GI food vs. foods with a low glycemic index?

When you consume a high GI index food:

  • Your body rapidly breaks down the carbs (starches and sugars) into glucose.
  • The glucose is then quickly absorbed in your small intestine so your cells can use it for energy.
  • This can result in your blood sugar spiking.
  • That then leads to an immediate increase of the hormone insulin.
  • Which then allows the cells of the body to use glucose for energy.


On the other hand, when you consume a low GI food or beverage, the spike in blood sugar and insulin is reduced. In other words, foods that have a high GI raise blood sugar more than medium GI foods which in turn raise blood sugar more than low GI foods.    

Can eating low glycemic index foods help people who have diabetes?

People who have type 2 diabetes have less insulin sensitivity — also known as insulin resistance — which means that their cells no longer fully respond to insulin. Because of this, glucose is not able to effectively enter their cells and, instead, it accumulates in their blood. In people who already have diabetes, eating a low-GI eating plan can help improve insulin sensitivity. That means that the body’s cells are more effective at using glucose, which then does not accumulate in the blood. There is also evidence that a low-GI eating plan can reduce HbA1c, the measure of long-term blood sugar control, as well as fasting blood sugar.

Can glycemic index diets prevent diabetes?

According to Mary Vouyiouklis Kellis MD, an endocrinologist in the Department of Endocrinology, Diabetes and Metabolism at Cleveland Clinic’s Endocrinology & Metabolism Institute, there have been several studies looking at the effects of a low glycemic diet. "A review of studies that followed the subjects over time and looked at GI and type 2 diabetes found that there was a protective effect for those eating lower glycemic index foods, plus a positive association between GI and the development of type 2 diabetes,” says Dr. Vouyiouklis Kellis.

In other words, the higher the glycemic index, the higher the risk of developing type 2 diabetes. And an analysis of the results from large, long-term studies (Nurses Health Study, Health Professionals Study) found that those who ate a diet ranked in the top 20% for GI also had a significantly higher risk of developing type 2 diabetes compared with those in the lowest 20%, says Dr. Vouyiouklis Kellis.

If you have prediabetes or are at risk for diabetes, should you try a low-GI eating plan?

Says Dr. Vouyiouklis Kellis, “For those patients with prediabetes or who are at risk for diabetes, I tell them to reduce refined sugars, which is essentially referring to high glycemic index foods, such as white breads, pastas, and white rice. I do not like to use the word diet as it can feel restrictive to patients. I discuss a lifestyle changes where I recommend healthier food choices, such as vegetables, whole grains, fruits, healthy sources of fat and lean proteins. I also tell them that this healthy lifestyle should be for everyone, not just for people with or at risk for diabetes.”

What’s the best low glycemic index diet?      

Dr. Vouyiouklis Kellis recommends including healthy vegetables, fruits, lean proteins, whole grains and healthy fats in your diet and suggests non-starchy vegetables, which include peppers, mushrooms, broccoli, lettuce, green beans and cauliflower. Lower glycemic index fruit include berries, cherries, apples and pears. According to Dr. Vouyiouklis Kellis, “If someone is considering this diet, they can use a glycemic index chart which lists the different food groups along with their GI. This may help them when they write out their grocery list and make choices on what to buy from the supermarket.” Click on this link for one such GI chart: 

Is there a downside to following a low glycemic index eating plan?

“The downside to the GI is that there are certain variables that can affect the GI,” says Dr. Vouyiouklis Kellis. “The rating is only for individual foods. For example, as fruit ripens, or if ood is prepared with fat or a protein, this can affect the GI ranking.”

A ripe banana has a higher GI than one that’s not as ripe. How you process the food also affects the GI. For example, a baked potato has a lower GI than mashed potatoes. A whole apple has a lower GI than apple juice. “In addition, it doesn’t rank foods based on nutrient content. Some foods that may have a low GI may be very high in calories. It is also difficult to follow GI because ackaged foods don’t provide GI on the label.” Still want to give it a go? Focus on adding low GI foods into your diet first, then cut down on the foods that are higher on the index.

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