Diabetes, Carbs, and The Glycemic Index: Your Guide to a Balanced Diet

Carbohydrates increase blood glucose levels,¹ but the rate at which they rise depends on the type and quantity of carbohydrates. What’s the difference between simple and complex carbohydrates, and how important is the glycemic index in your daily diabetes routine? Find the answers here!

Simple carbohydrates, also known as fast-acting carbs, are easily digested by the body and pass into the bloodstream from the gut more quickly, causing blood glucose levels to rise rapidly.² Simple carbohydrates are found in sweets, cold drinks, cookies, and many convenience products.³

Complex carbohydrates, or slow-acting carbs, on the other hand, take a long time to digest, causing blood glucose levels to gradually increase.² They can be found in fruits, vegetables, whole-grain products, and legumes.³

People with diabetes need to be more mindful of the types of carbohydrates they consume. Slow-acting, complex carbohydrates are more suitable than simple carbohydrates for maintaining a uniform glucose supply.⁴ Without complex carbs, fluctuations in blood glucose levels have been linked with adverse health outcomes.¹

What carbohydrates are in my food?

The nutrition facts label is helpful for packaged products: “carbohydrates” indicates the total value for all sugars.⁵ “Of which sugars” refers to simple carbohydrates, including monosaccharides and disaccharides.⁶ 

People who have to inject insulin need even more precise information. To determine the optimal hormone intake levels, it is necessary to understand the precise impact of simple and complex carbohydrates on blood glucose levels.⁵ This is where the glycemic index and glycemic load come in:⁷

• The glycemic index (GI) indicates the rate at which a specific type of food increases the blood glucose level.
• The glycemic load (GL) refers to the amount and type of carbohydrates in your diet as well as their impact on blood sugar levels after you eat. It provides a more comprehensive picture than the glycemic index, which only considers how carbohydrates affect blood sugar and ignores portion size.

The glycemic index (GI) can be used to guide diets for people who have heart disease or diabetes. A dietary pattern that triggers an increased glucose response is associated with the development of coronary heart disease and type 2 diabetes.^8,9 Therefore, a diet with a low GI/GL, in combination with other health interventions, could help reduce health risks for people with such conditions.

It's important to note that there is no "one size fits all" approach. Post-meal glucose levels can vary significantly from person to person, even when they consume the same foods. This means that diets need to be specific to each person.¹⁰

GI is designed to help you choose the right foods or set the right insulin amount:

• Carbohydrates with a low GI cause blood glucose levels to rise slowly.⁷

• A high GI, however, means that the blood glucose level increases rapidly after eating.⁷

People with diabetes should favor foods with a low glycemic index, ensuring that their nutritional content aligns with the recommended dietary guidelines for fiber, sugars, saturated fats, and protein.⁴

Some studies indicate that a diet with a low GI can improve blood glucose levels and insulin sensitivity in people with type 2 diabetes.⁹

People with diabetes should favor foods with a low glycemic index.¹¹ Studies also demonstrate that a diet with a low GI can improve blood glucose levels and insulin sensitivity.¹¹ 

Choosing foods and their glycemic index

The glycemic index (GI) is used as a guide for choosing high-quality carbohydrates.⁷ The GI is stated as a percentage and is calculated based on how quickly a specific type of food increases blood glucose levels. 

The GI of glucose is set to 100% for the purposes of this calculation.

The GI rankings are as follows:¹² 

• Low: less than 55 percent
• Middle: 55 to 70 percent
• High: over 70 percent

If you have diabetes, this table can help you plan meals by showing the glycemic index of commonly consumed carbohydrates in order of decreasing glycemic value.¹²

Generally, food with a high glycemic value is of lesser quality, while food with a low glycemic value is of greater quality. However, additional factors, such as total fiber content and nutritional density, should also be taken into account.⁴

The glycemic index gives you a first impression of the effect of carbohydrates in a specific type of food on blood glucose levels.⁷ When using the list, take into consideration, for example, the GI for watermelon is high because the GI always refers to 50 grams of carbohydrate in a specific food.¹² That means you would have to eat quite a lot of watermelon—over 800 grams, to reach the level of 50 grams of carbohydrate. Therefore, the glycemic index is used in conjunction with the glycemic load, which takes into account the actual amount of food eaten.

In addition to the difficulties in comparing foods (since GI refers to weight), there are other downsides to the glycemic index that make it less than ideal^12,13:

• For fruits and vegetables, the effect on our blood glucose levels is also influenced by the region in which they are produced, their maturity, and variety.
• You usually eat several different foods per meal, so a meal also includes fat, protein, and dietary fiber, which slows down the absorption of carbohydrates in the blood. For diabetes, this means performing an additional calculation of the fat protein unit (FPU), which can make it much easier to determine the insulin dose.
• How food is processed and prepared can also influence its impact on blood glucose levels. The reference to “al dente” under pasta in the GI table relates to this. The GI value of spaghetti varies depending on whether it is cooked to al dente or soft. Generally, heated foods have a higher glycemic index than unheated foods.
• In other words, the glycemic index has limited use in the daily routine for people with diabetes. It’s more important to think of it as a guide to a balanced diet.

It’s not just the quantity of food that influences blood glucose levels; it's more about the amount of carbohydrates the body absorbs.⁷ But how do you determine that?

To calculate, you start by referring to the glycemic index.⁷ The glycemic load is calculated by multiplying the GI by the number of carbohydrates per serving (grams) and then dividing by 100.¹⁴

The result can serve as a guide on how carbohydrate-containing foods affect blood glucose levels. The glycemic load rankings are as follows¹⁵:

• Low: up to 10

• Moderate: 10 to 20

• High: 20 or higher

People with diabetes are encouraged to follow a low-GI diet when its composition aligns with general dietary guidelines for fiber, sugar, protein, and saturated fat.

Some data also suggest that a diet containing higher GI foods increases the risk of diabetes. In such cases, a healthcare professional's advice on slow dietary adjustments might be helpful.⁴

There is also some evidence that a higher GI diet may increase the risk of diabetes.¹⁶ Unless they have impaired renal function, people with diabetes may want to limit high-sugar foods and favor those with a low glycemic load.¹⁷

To clarify, people with diabetes can generally eat anything.⁴ However, adapting diabetes therapy to a person's lifestyle and eating habits to create a balanced diet that meets nutritional needs is recommended more often.

There is no precise recommended amount of carbohydrates, as the impact on blood glucose can vary from person to person.¹⁰ Medication and insulin treatment vary significantly from patient to patient.¹⁸

Experts from the Diabetes and Nutrition Study Group (DNSG) of the European Association for the Study of Diabetes (EASD) advise people with type 2 diabetes to limit their carbohydrate intake and follow a low-carbohydrate diet, such as a Mediterranean-style diet.^4,9  Experts advise people with type 2 diabetes to restrict carbohydrate intake to around 45 percent of their daily energy intake.¹⁹ This is advised as some of those affected struggle to compensate for a higher carbohydrate load.¹⁹

The most recent evidence suggests that a low-carbohydrate diet may improve glucose metabolism.⁴ This can refer to a diet in which less than 40% of total energy intake comes from carbohydrates, depending on the exact definition.²⁰ However, extreme, very-low-carbohydrate diets, such as ketogenic diets, are not recommended because they have not shown significant benefits in preventing or managing type 2 diabetes and pose potential safety risks.

 Carbohydrates from vegetables, legumes, fresh fruit, and whole-grain products are particularly recommended for people with diabetes, as they are rich in dietary fiber, which helps slow the rise in blood glucose levels.

Sources:

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