The glycemic index is a scale that ranks the number of carbohydrates in foods from zero to 100, indicating how quickly a food causes a person's blood sugar to rise.
Foods high on the glycemic index (GI) can cause harmful blood sugar spikes in people with diabetes. High GI foods also make it more challenging for a person to maintain a healthy weight. This is why some people with diabetes use GI to plan their meals.
A nutritious, balanced diet includes a wide range of foods, so a person is not limited to consuming just low GI foods. However, knowing where a specific food rests on the GI can help a person make healthful choices.
In this article, learn more about GI, as well as about high and low GI foods.
The GI provides information about how the body digests carbohydrates using a scoring system of zero to 100. Pure sugar has a score of 100.
Nutrition experts used to classify carbohydrates as either complex or simple. For example, table sugar is a simple carbohydrate, while beans and grains are complex carbohydrates.
While researchers once believed that complex carbohydrates were less likely to cause blood glucose spikes, further research found that the relationship between carbohydrates and blood glucose is more complex.
GI accounts for this complexity by ranking foods according to how quickly they elevate blood sugar.
To assess GI, researchers gave volunteers without diabetes a test food that contained 50 grams (g) of carbohydrates. On a different day, they gave participants a control food, such as white bread or sugar, that has the same amount of carbohydrates.
They then compared blood sugar levels at regular intervals for both foods, which means GI is simply a way to compare the effect of various foods on blood glucose.
The higher a food's GI is, the more rapidly it elevates blood glucose. A high GI food can cause blood sugar spikes, followed by rapid declines in blood sugar.
As blood sugar declines, a person may feel hungry. Eating only high GI foods can cause a person to overeat since they will quickly feel hungry again after eating.
Eating a diet with a low average GI may reduce a person's risk of developing diabetes and heart disease. In people who already have chronic conditions, a low GI diet may reduce the risk of complications and prevent blood glucose spikes.
The GI scores are as follows:
- low GI foods: 55 or less
- medium GI foods: 56–69
- high GI foods: 70 or above
The Glycemic Index Foundation suggest that aiming for an average dietary GI score of 45 may offer the most significant health benefits.
This does not mean that a person can only eat foods with a GI score of 45 or lower. Rather, a person should balance their intake of higher GI foods by eating foods with a lower GI.
It is important to note that the GI of a specific food is an estimate. Several factors can affect the GI of a given food:
- Cooking tends to raise GI. The same type of pasta will have a lower GI if it is al dente than it will if a person cooks it to the point of softness.
- Processing typically raises GI. For example, fruit juice typically has a higher GI than whole fruit.
- Riper foods usually have a higher GI. The GI of a banana, for example, will get higher as the banana ripens.
- The foods a person eats together can affect GI. Fiber lowers the total GI of a meal.
Some examples of low GI foods include:
Foods with a higher GI include:
- heavily processed grains, such as white rice, white bread, and white pasta
- puffed rice
- instant oatmeal
- saltine crackers
- starchy vegetables, such as potatoes
- corn flakes
- bran flakes
The GI can help a person make healthful decisions about their overall diet and nutrition.
People with diabetes, those trying to lose weight, and people at risk of heart disease can reap significant benefits from a low GI diet, though the benefits extend to everyone — not just people with chronic illnesses.
Eating a low GI diet does not have to mean avoiding all high GI foods. Instead, a person's goal should be to stay balanced over time, with a strong focus on fiber-rich foods with a low GI. A doctor or dietitian can help with planning a delicious and nourishing diet that features a wide variety of low GI foods.