What Is the Connection Between Glycaemic Index and Insulin Resistance?

In nutrition, carbohydrates are known as one of the body’s primary sources of energy. The carbohydrates in the foods we eat are broken down during digestion into simple sugars, mainly glucose, which then enter the bloodstream to provide fuel for our cells. However, the body does not respond to every carbohydrate in the same way. How quickly glucose enters the bloodstream and how effectively our cells respond to it are important aspects of metabolic health.

Let’s take a closer look at the Glycaemic Index (GI), which describes how carbohydrate-containing foods affect blood glucose levels, and its biochemical relationship with insulin resistance, one of the most common metabolic health concerns today.

What Is the Glycaemic Index (GI)?

Carbohydrates are broken down during digestion into simple sugars, including glucose, which enter the bloodstream and can then be used by cells for energy. The Glycaemic Index (GI) is a ranking system that describes how quickly and how much a carbohydrate-containing food raises blood glucose compared with a reference food.

High-GI foods, generally classified as having a GI of 70 or above, can cause a relatively rapid rise in blood glucose. Foods such as baked potatoes and white bread often fall into this category because their starches can be readily digested by digestive enzymes.

In contrast, low-GI foods, generally classified as 55 or below, tend to produce a slower and more gradual rise in blood glucose. Oats, lentils and green bananas are examples of foods that may have lower glycaemic responses.

The ripeness of a food can also influence its glycaemic properties. In bananas, for example, some of the starch present in the unripe fruit is converted into sugars as the fruit ripens. As a result, green bananas generally produce a lower glycaemic response than ripe bananas. Low-GI foods may therefore help reduce sharp fluctuations in blood glucose and, depending on the overall composition of the meal, may also contribute to prolonged satiety.

What Are Insulin and Insulin Resistance?

Insulin is a hormone produced by the pancreas that plays a central role in regulating blood glucose levels. After a meal, as glucose levels in the blood rise, the pancreas releases insulin.

Insulin helps glucose move from the bloodstream into muscle and fat cells, where it can be used or stored for later energy needs. It also influences glucose production and storage in the liver and plays an important role in fat metabolism.

Insulin resistance, also described as reduced insulin sensitivity, is a complex metabolic condition in which tissues such as muscle, liver and adipose tissue do not respond to insulin as effectively as they normally would.

When insulin signalling becomes less effective, the body needs more insulin to achieve the same glucose-regulating effect. In response, the pancreas may compensate by producing additional insulin, resulting in elevated circulating insulin levels, a state known as hyperinsulinaemia.

As long as the pancreas can produce enough additional insulin, blood glucose may remain within the normal range. However, if insulin resistance progresses and pancreatic beta cells can no longer compensate sufficiently, blood glucose levels may begin to rise. Persistent hyperglycaemia can eventually contribute to the development of prediabetes and type 2 diabetes.

So, How Can a Low-GI Diet Influence Insulin Sensitivity?

The relationship between dietary GI and insulin resistance involves several interconnected metabolic pathways rather than a single mechanism.

Regular consumption of rapidly absorbed, high-GI carbohydrates can produce greater post-meal increases in both blood glucose and insulin. Over time, dietary patterns characterised by high glycaemic exposure may contribute to metabolic conditions associated with impaired insulin sensitivity.

Elevated circulating free fatty acids and the accumulation of lipid metabolites in tissues such as the liver and skeletal muscle are also known to interfere with normal insulin signalling and can contribute to insulin resistance.

Low-GI dietary patterns, on the other hand, generally produce smaller and more gradual post-meal glucose and insulin responses. When incorporated into an overall balanced diet, they may help support glycaemic control and insulin sensitivity.

A recent systematic review and meta-analysis reported that lower-GI dietary interventions were associated with improvements in insulin resistance even among adults without diabetes, further highlighting the potential role of carbohydrate quality in metabolic health.

References

1.   Yu, Y. T., Fu, Y. H., Chen, Y. H., Fang, Y. W., & Tsai, M. H. (2025). Effect of dietary glycemic index on insulin resistance in adults without diabetes mellitus: a systematic review and meta-analysis. Frontiers in nutrition, 12, 1458353. https://doi.org/10.3389/fnut.2025.1458353
2. Kim, D. (2020). Glycemic index. In Obesity (pp. 183-189). Elsevier.
3. Augustin, L. S., Franceschi, S., Jenkins, D. J. A., Kendall, C. W. C., & La Vecchia, C. (2002). Glycemic index in chronic disease: a review. European journal of clinical nutrition, 56(11), 1049-1071.