For years, the glycemic index has been a topic of interest in the fields of nutrition and health, while “low glycemic index” products are increasingly being promoted as healthier choices. In this article, we will explain what the glycemic index is, which foods are classified as having a low or high glycemic index, and explore whether it is ultimately an important factor for well-being.

What is the glycemic index?

Scientific definition: The glycemic index is defined as the area under the glucose response curve following the consumption of 50 grams of carbohydrates from a test food, divided by the area under the curve following the consumption of 50 grams of carbohydrates from a reference food, either white bread or glucose.

Simply put, the glycemic index represents how quickly a food raises blood sugar levels after it is consumed. It ranges from 0 to 100. For example, when a food has a glycemic index of 45, consuming 50 grams of carbohydrates from that specific food raises blood glucose concentrations to 45% of what would occur if 50 grams of glucose were consumed.

What do we mean by “low glycemic index foods”?

“Low glycemic index foods” are those with a glycemic index of 55 or lower. In other words, these foods raise blood sugar slowly. Some low glycemic index foods are listed below.

Fruits: apple, pear, orange, peach, plums, strawberries, blueberries, grapefruit

Vegetables: broccoli, cauliflower, tomato, cucumber, peppers, lettuce, spinach, eggplant, zucchini

Legumes: all legumes

Starchy foods: oats, barley bread, multigrain bread, al dente pasta, quinoa, barley, rye bread, sweet potato

Dairy products: Greek yogurt, milk, kefir

What do we mean by “medium glycemic index foods”?

“Medium glycemic index foods” are those with a glycemic index between 56 and 69. In other words, these foods raise blood sugar at a moderate rate when consumed. Indicative examples include the following.

Fruits: ripe banana, pineapple, raisins, papaya, dried figs, mango, kiwi, grapes

Vegetables: beets, corn

Legumes: none fall into this category

Starchy foods: basmati rice, brown rice, couscous, semolina, white rice (short- and long-grain varieties), wild rice, French fries

Dairy products: chocolate milk

What do we mean by “high glycemic index foods”?

“High glycemic index foods” are those with a glycemic index of 70 or higher. In other words, these foods raise blood sugar rapidly. Such foods include the following.

Fruits: watermelon

Vegetables: none fall into this category

Legumes: none fall into this category

Starchy foods: white bread, Corn Flakes cereal, jasmine rice, millet, instant mashed potatoes, potato chips, savory crackers, pretzels

Dairy products: rice milk (not actually a dairy product, but it is often found in the refrigerated dairy section of supermarkets)

Finally, meat, poultry, fish, and cheese do not have a glycemic index value because they do not provide carbohydrates.

Why is the glycemic index important?

In general, the role of the glycemic index has been studied in individuals with type 1 diabetes and type 2 diabetes, but it is also relevant to the diet of the healthy population.

More specifically, foods with a high glycemic index cause a rapid increase in blood glucose, resulting in the secretion of a large amount of insulin by the pancreas. It should be noted that insulin is the hormone responsible for transporting glucose into cells so that it does not circulate freely in the bloodstream and cause damage to blood vessels. Consequently, excessive insulin secretion may subsequently lead to a rapid drop in blood sugar levels, known as reactive hypoglycemia, and increased appetite, both in individuals with insulin-dependent diabetes mellitus (who receive exogenous insulin) and in the general population. In addition, elevated levels of insulin in circulation contribute to the development of insulin resistance, a condition in which cells no longer respond effectively to insulin and glucose remains outside them. Insulin resistance is associated with issues such as increased fat storage, prediabetes, diabetes mellitus, cardiovascular disease, inflammation, and hormonal disorders.

Therefore, choosing foods with a medium or low glycemic index helps maintain insulin levels within a normal range and may prevent the adverse conditions described above.

Which factors affect the glycemic index?

The glycemic index is influenced by the following factors:

1. The physical form of the food: A characteristic example is linguine. Thick linguine has a glycemic index of 68, whereas thin linguine has a glycemic index of 87.
2. Ripeness: Ripe fruits have a higher glycemic index than unripe fruits, which is easy to understand because they taste sweeter. A typical example is the banana. A ripe banana has a glycemic index of 51, whereas an unripe banana has a glycemic index of 42.
3. Food preparation method: The cooking method and the level of food processing influence the glycemic index. Baking is preferable to boiling. For example, a baked potato has a glycemic index of 54, while mashed potato has a glycemic index of 67. Likewise, al dente pasta is preferable to pasta cooked for the standard cooking time.
4. Manufacturing process: This factor relates to processed foods and the way they are produced in factories in different countries. Therefore, a chocolate bar manufactured in the United States may have a higher glycemic index than a chocolate bar of the same brand manufactured in the United Kingdom.
5. Type of carbohydrate: Foods containing higher amounts of simple carbohydrates (such as glucose and fructose), for example white bread, have a higher glycemic index compared with foods that contain more dietary fiber, such as whole-grain products.

What should we do in practice regarding the glycemic index?

We should favor foods with a medium or low glycemic index because, as mentioned above, they can contribute to better metabolic health and more stable energy levels throughout the day.

Therefore, from the starchy foods group, we choose multigrain whole-grain bread, rolled oats, basmati rice, legumes, and starchy vegetables such as peas and sweet potatoes. From the fruit group, we choose apples, oranges, pears, peaches, and apricots, while from the dairy group we choose milk and yogurt. We should also remember that the glycemic index depends on the cooking method, so we prefer baking, boiling, or steaming foods, provided that they are not overcooked.

 

References

1. Atkinson, F.S., Brand-Miller, J.C., Foster-Powell, K., Buyken, A.E. and Goletzke, J., 2021. International tables of glycemic index and glycemic load values 2021: a systematic review. The American Journal of Clinical Nutrition, 114(5), pp.1625–1632.
2. Jenkins, D.J.A., Dehghan, M., Mente, A., Bangdiwala, S.I., Rangarajan, S., Srichaikul, K., Mohan, V., Avezum, A., Díaz, R., Rosengren, A., Lanas, F., Lopez-Jaramillo, P., Li, W., Oguz, A., Khatib, R., Poirier, P., Mohammadifard, N., Pepe, A., Alhabib, K.F., Chifamba, J., Yusufali, A.H., Iqbal, R., Yeates, K., Yusoff, K., Ismail, N., Teo, K., Swaminathan, S., Liu, X., Zatońska, K., Yusuf, R. and Yusuf, S., for the PURE Study Investigators, 2021. Glycemic index, glycemic load, and cardiovascular disease and mortality. The New England Journal of Medicine, 384(14), pp.1312–1322.