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What Affects the Glycemic Index (GI) and Response?

Article author photo Victoria Mazmanyan by Victoria Mazmanyan | Last updated on July 20, 2022
Education: General Medicine at YSMU

What Affects the Glycemic Index and Response?

The glycemic response of a meal is not affected only by its carbohydrate content but other nutrients as well. Knowing how different foods interact with each other can have significant practical benefits. In balanced meals, certain macronutrients can reduce the glycemic response of high glycemic index foods.

Overall, research finds fat, protein, and dietary fiber to reduce but lengthen the glycemic response of meals, lowering the glycemic index (1, 2, 3).


Research shows that meals with a higher fat content induce a smaller increase and a slower drop of postprandial glucose concentrations than a high-carbohydrate, low-fat meal (4). This might result in a lower glycemic index of a meal.

Adding dietary fat to a meal reduces its early glucose response and delays peak blood glucose. This is due to fat’s ability to delay stomach emptying (5).

The delayed peak blood glucose leads to late postprandial hyperglycemia, which must be accounted for in people with type 1 diabetes to calculate the correct required insulin dose (5).

The chain length and saturation of fats can play a significant role in the glycemic response to a meal (6). Adding polyunsaturated fatty acids to a meal reduces the glycemic response more than saturated or monounsaturated fats (7, 8).

However, the glucose-lowering effect of fat may be attenuated or absent in individuals with type 2 diabetes (9).


Adding protein to a meal can also significantly affect its glycemic response (1, 2, 5).

The results of short-term studies have demonstrated several beneficial effects of the intake of high-protein diets (22 to 30% of daily calorie intake) from different sources (animal or vegetable) on glycemic control (10).

However, these effects may be particularly associated with the consumption of animal protein with a high content of branched-chain amino acids such as leucine, valine, and others such as arginine (10).

Protein reduces glycemia after eating by delaying gastric emptying and enhancing insulin secretion. This results in a lower postprandial glucose peak and a reduced glycemic response to a high glycemic index food (11).

One study concluded that gram per gram, protein reduces the glucose response 2 times more than fat (2).

Dietary Fiber

Dietary fiber is a form of carbohydrates classified as unavailable, as these carbohydrates do not get absorbed into the bloodstream and do not directly raise blood glucose levels. However, dietary fiber affects the glycemic response indirectly by slowing down the breakdown and absorption of available carbohydrates, such as free sugars and complex carbohydrates.

Research has found total dietary fiber to be significantly associated with the glycemic index. Insoluble fiber is more closely related to the glycemic index compared to soluble fiber (12).

Among soluble fibers, sources of highly viscous soluble fiber, such as cluster beans, are more effective in reducing blood sugar than non-viscous fiber sources, such as wheat and apples (13, 14).

High dietary fiber intake also enhances the glucose-lowering effects of protein. A high fiber intake may be associated with increased insulin secretion in response to protein ingestion (2).

Cooking Methods

Besides the nutritional content of meals, different cooking methods can also change the glycemic index and response.

Freshly prepared food may result in a relatively higher glycemic response than reheated meals due to changes in the physicochemical characteristics (15).

In one study, cooking rice caused a slight increase in the glycemic index compared with the raw samples (16).

Liquid forms of foods may also result in a higher glycemic response. Liquid diets do not require chewing and could present faster intestinal transit and absorption, resulting in more postprandial glycemic increase compared to diets with solid consistency (10).


Article author photo Victoria Mazmanyan
Education: General Medicine at YSMU
Last updated: July 20, 2022
Data provided by should be considered and used as information only. Please consult your physician before beginning any diet.