Watermelon, cooked carrots and bananas – facts and myths about their glycaemic index

The glycaemic index (GI) indicates the effect of a food on the increase in blood glucose concentration after consumption. It indicates by how much the blood glucose concentration will rise after eating 50 g of carbohydrates of a given product.

The standard is glucose, which has a GI of 100, so the GI scale is from 0 to 100. A value of up to 50 indicates a low GI, a value between 50 and 70 indicates a medium GI, and a value above 70 indicates a high GI.

Watermelon, like other fruits, contains natural sugars. However, watermelon does not have a particularly high content of natural sugars, they are around 7%. Watermelon consists mainly of water. Other fruits such as mango or banana (13% sugar), red grapes (16%) or pear (12%) have a much higher carbohydrate content.

In previous GI tables, watermelon was listed as a high-GI product (76), and we know that high-GI products need to be eaten with caution as they can raise blood glucose levels, especially in people with diabetes.

The latest glycaemic index tables published in 2021 show that watermelon has a low GI of 50, based on an average of four varieties. This fruit does not raise glucose as much as previously thought. With this change, people with diabetes and insulin resistance can also include watermelon in their diet.

Carrots are a non-starchy vegetable that form an essential part of a healthy diet. It contains essential vitamins, minerals, fibre and antioxidants. Carrots have a high fibre content. Thus, it helps to slow carbohydrate absorption and control glucose spikes after a meal. Managing blood sugar levels is the main goal of diabetes treatment.

The fibre content of carrots also helps to control body weight. This is possible by reducing hunger attacks. Depending on how they are served, carrots have different glycaemic indexes. Raw whole carrots have a glycaemic index of 16, raw and diced carrots 35, cooked carrots 33 and carrot juice 43.

Carbohydrates that break down quickly during digestion have a higher glycaemic index. Factors such as size, texture, viscosity (internal friction or ‘thickness’) and maturity of the food affect its GI. Cooking and processing can also affect the GI – foods broken into smaller or finer particles will be more easily absorbed and therefore have a higher GI. However, in the case of carrots, cooking does not significantly raise the glycaemic index.

Bananas are an excellent source of potassium, a mineral essential for heart health. Potassium helps regulate blood pressure and prevents the risk of heart disease. They are also a rich source of dietary fibre. Bananas are packed with antioxidants, including dopamine and catechins, which can help reduce inflammation in the body. This can help prevent chronic diseases such as arthritis and cancer.

The glycaemic index of a banana can vary depending on factors such as ripeness, variety and size. In general, the riper the banana, the higher its GI. Ripe bananas have a low GI of 51, while slightly unripe bananas have an even lower GI of 42.

However, the type of carbohydrate contained in bananas is classified as resistant starch , which acts similarly to dietary fibre. Resistant starch is not broken down in the small intestine, so less glucose is released into the bloodstream. This results in a lower glycaemic index and a greater feeling of satiety because the starch is digested slowly.

Therefore, let’s eat these products for health!

Zuzanna Cybulska