What is the Glycemic Index?
You may have heard of the glycemic index (GI), a tool that measures how certain foods impact blood sugar levels. But it can be tough to understand what GI values mean or how they may impact your daily eating.
While GI can be helpful, it’s not a perfect guide for healthy eating, and does not translate to diet recommendations for everyone.
“Foods with a high glycemic index value are not necessarily unhealthy, and not all foods with a low glycemic index value are healthy,” says registered dietitian Kaylee Seekon, RD, a pediatric diabetes educator at the Naomi Berrie Diabetes Center. “Your focus should be creating a healthy, balanced diet and finding foods that make you feel good.”
Seekon addresses common glycemic index questions and explains the importance of looking beyond GI to an overall balanced diet.
What is the glycemic index?
The glycemic index (GI) is a measure of how quickly a food causes our blood sugar levels to rise after eating, based on a scale of 0 to 100.
High GI foods, like pretzels (glycemic index of 83), are quickly digested and absorbed, leading to a swift spike in blood sugar.
Low-GI foods, like Greek-style yogurt (glycemic index of 11), are metabolized more gradually, resulting in a slower and more sustained increase in blood glucose. That said, low glycemic index does not necessarily equal high nutritional value. Always choose a variety of foods, from all five food groups, to have a healthy, balanced diet.
What is a low-glycemic index diet?
A low glycemic index value is less than 55. People refer to that as “good” glycemic index and create diets around it, but that is not right for everyone and is not the only thing to consider when eating. Talk to a dietitian if you want to know if a glycemic index-based diet is right for you.
Should you focus on foods with lower glycemic index values?
This is a question for your doctor, nurse, or nutritionist, who can help figure out what’s best for you.
In general, eating is not one-size-fits-all—everybody reacts differently to different foods. So, using the glycemic index as a guide is not a one-size-fits-all approach to health.
In addition, foods with a high GI are not necessarily unhealthy (watermelon, for example, is a "high" GI food). And not all foods with a low GI are healthy (chocolate cake has a "low" GI value). Instead, the focus should be creating a healthy, balanced diet.
There are ways to make “high glycemic foods” better for you by watching portion sizes and pairing with protein and fiber.
What can you do to manage blood sugar?
My biggest piece of advice is to always pair carbohydrate foods with protein or fat. A few examples of snacks and meals that combine carbs with protein or fat include:
- Popcorn with nuts
- Toast with cottage cheese
- Chips with a cheese stick
Pairing starchy food (like rice or pasta) with protein, fiber, or healthy fat (like beans, vegetables, or avocado) can reduce the glycemic impact of a meal.
What is the glycemic index of white rice?
Many people have questions about rice. Rice is often unfairly demonized in nutrition conversations, especially when it comes to blood sugar. However, it can absolutely fit into a balanced, blood sugar-friendly meal. Rice provides carbohydrates for energy and contains small amounts of protein, fiber (depending on the variety), and essential nutrients like B vitamins and magnesium.
On the glycemic index chart, white rice has a value of 70, making it a high glycemic index food item.
But instead of stressing over whether you should or shouldn’t eat rice, let’s shift the focus to what you can add to make it more blood sugar friendly. Pair rice with a protein (like chicken, tofu, or eggs) and fiber (like vegetables, beans, or seeds) to help slow digestion and reduce post-meal blood sugar spikes. And be mindful of portion size—½ to 1 cup of cooked rice per person is a good starting point.
Does refrigerating rice lower its glycemic index?
Yes. Cooling a starch like rice after cooking it is a science-backed strategy. When rice is cooled, retrogradation occurs, which is a process that turns some digestible starch into resistant starch. Resistant starch behaves more like fiber in the body, slowing the release of glucose into the bloodstream and helping to improve gut health. If you plan to eat rice, you can make it a day or two before, put it in the fridge, then reheat when ready to use (reheating doesn't significantly decrease the amount of resistant starch).
Should you think about your blood sugar when you eat and drink?
Unless you have diabetes (such as type 1, type 2, or pre-diabetes) or another specific health condition, there's no need to excessively focus on how food impacts your blood sugar. It's completely normal for carbohydrate-containing foods to raise blood sugar levels; this is a natural physiological response.
Instead, it's more important to consider the overall quality of your diet and look for opportunities to enhance its nutritional value. The best approach to nutrition is eating a balanced diet of meals that contain fiber-rich carbs, protein, and heart-healthy fats.
How do you calculate glycemic index from food labels?
You cannot calculate the GI from a food label.
Is the glycemic index perfect?
No. Though it is widely referred to, the glycemic index is slightly flawed.
One flaw is that the glycemic index is based on eating one food at a time. Most of us don't eat that way. A typical diet consists of food mixtures. Protein and fat don't really affect blood sugar, so the glycemic index of these foods will be low. For example—and this is a good thing—adding peanut butter to an apple for a snack changes the food GI.
And the glycemic index doesn't tell you how high your blood sugar could go when you actually eat a food, nor does it consider other factors, like how it was prepared or ripeness (more ripeness equals more sugar). These are all things that can affect blood sugars.
Kaylee Seekon, MS, RD, CDN, CDCES, is a pediatric diabetes educator at the Naomi Berrie Diabetes Center.