How Different Types of Carbohydrates Affect Blood Sugar and Performance | Hardworkout Magazine

Key takeaways

- Carbohydrates account for about 45–60% of daily energy needs, and the quality of those carbohydrates matters more for blood sugar and satiety than the quantity alone.

- Foods with a glycaemic index of 70 or above cause a rapid rise in blood sugar, while foods at 55 or below raise it slowly; glucose sits at 100 on the scale.

- Glycaemic load is a more precise measure than glycaemic index because it accounts for the carbohydrate content of an actual portion — watermelon has a GI of 72 but a GL of just 4.

- Eating protein and fat alongside carbohydrates slows digestion and glucose absorption, so even fast carbohydrates produce a smaller blood sugar spike when they are not eaten alone.

- A 2025 study found that a diet with a low glycaemic load improved insulin sensitivity and gave better regulation of both blood sugar and blood lipids.

Carbohydrates account for about 45–60% of daily energy needs, and it is therefore wise to choose the right type for optimal energy, health, and weight management. The quality of carbohydrates is more important than the quantity alone, especially regarding blood sugar and satiety.

Whether you train actively, have a busy everyday life, or just want a stable energy level, it is important to understand how food affects your blood sugar and to choose the right carbohydrates that provide sustained energy and support recovery.

What is the difference between fast and slow carbohydrates?

Carbohydrates are one of the 3 main nutrients (macronutrients) from which we derive energy, in addition to fats and proteins.

When we consume carbohydrates from food, they are broken down into glucose in the body and used as energy in our cells.

There are several different types of carbohydrates; sugars, fibers, and starches – which have different effects on blood sugar levels.

Not all types of carbohydrates provide you with the same energy, and the difference between fast and slow carbohydrates can significantly affect mood, energy, and performance.


Fast Carbohydrates

Fast carbohydrates provide a short-term energy boost, but the energy level drops quickly again, especially if the carbohydrates are consumed without other nutrients.

They are quickly broken down and absorbed rapidly into the blood, which leads to a rapid spike in blood sugar.

Typical unhealthy sources of fast carbohydrates include white bread, sugary drinks, candy, pastries, and cakes.

Other more nutrient-rich carbohydrates that are absorbed quickly can be bananas, raisins, rice cakes, and sports drinks, which are beneficial to consume in connection with exercise for a quick replenishment of energy.

Slow Carbohydrates

Slow carbohydrates break down more slowly and therefore provide a more even and stable rise in blood sugar. They thus offer a better and more lasting feeling of fullness and energy.

This type of carbohydrate provides the body with fuel that lasts longer, even during physical activity, and can therefore lead to better performance and achievement when you train.

Examples of nutritious and slow carbohydrates include sweet potatoes, oats, whole grain products (bread, rice, pasta), and legumes (beans, lentils, and chickpeas).

Glycemic Index (GI)

The glycemic index is a measure of how quickly blood sugar rises after consuming a carbohydrate-rich food. The scale ranges from 0 to 100, with glucose (sugar) having a value of 100.

Foods that have a GI of 70 or more are considered high GI and will cause a rapid increase in blood sugar.

Examples of foods with high GI include white bread, baked potatoes, cornflakes, sugary soda, beer, juice, and rice cakes.

Foods that have a GI of 55 or lower are considered low GI and will cause a slow increase in blood sugar.

Foods with low GI can include lentils, apples, sweet potatoes, whole grain pasta, and plain yogurt.


Examples of GI in composite meals

- Oatmeal cooked in milk, topped with almonds and blueberries (GI 45)

- Salmon with sweet potato mash and steamed vegetables (GI 55-60)

- Baked potato with butter and ketchup (GI 85)

The values provided may vary slightly depending on the sources they are taken from, but they give an indication of which part of the scale they belong to.

Glycemic Load (GL)

Glycemic load takes into account both the amount of carbohydrates and the GI in a portion, and will therefore be a more precise measure of how this food affects blood sugar.

A food item can have a high GI but still a low GL if it contains few carbohydrates per serving, such as watermelon.

Watermelon has a GI of 72 but a GL of 4, since it contains few carbohydrates and calories per 100 g.

GL for entire meals will also be affected by other nutrients that you consume in addition to the carbohydrates.

When carbohydrates are combined with fats and proteins, it will reduce the overall glycemic load.

The reason for this is that proteins and fats slow down digestion and glucose absorption, thereby dampening the blood sugar rise.

Even fast carbohydrates will cause a smaller blood sugar spike if consumed together with proteins and fats, compared to if they are consumed alone.

Classification of Glycemic Load

- Low GL: 10 or less per 100 g of food

- Moderate GL: 11-19 per 100 g of food

- High GL: 20 or more per 100 g of food

Foods with low GL can include lentils, chickpeas, apples, plain yogurt, and sweet potatoes.

Examples of foods with moderate GL are bananas, oatmeal, whole grain pasta, and brown rice.

Examples of foods with high GL are white bread, baked potatoes, rice cakes, and sugary soda.


How does meal composition change the glycaemic load?

How you combine meals with proteins, carbohydrates, and fats will also result in different glycemic loads.

Meals with low GL

- Chicken salad with lentils, tomatoes, spinach, and olive oil.

- Plain yogurt with berries and nuts.

- Oven-baked sweet potato with chickpeas and tahini.

Meals with moderate GL

- Oatmeal with banana and almond butter.

- Steamed salmon with whole grain pasta, arugula, and pesto.