Glycemic index
The glycaemic index (GI) is a measure of how quickly a carbohydrate-containing food causes blood sugar levels to rise. The higher the GI, the faster and stronger the rise in blood sugar after eating. The concept helps to better assess foods and understand blood sugar fluctuations that affect energy, hunger and mood.
What is the glycemic index?
The glycemic index (GI) was developed in the early 1980s by Canadian nutritionist David Jenkins. It describes how much 50 grams of digestible carbohydrates in a food raise blood sugar levels compared to pure glucose (GI = 100). Foods are divided into three categories:
- Low GI (below 55): e.g., legumes, most vegetables, oatmeal, whole-grain bread
- Medium GI (56–69): e.g., basmati rice, bananas, whole-grain pasta
- High GI (70 and above): e.g., white bread, cornflakes, soft drinks, parboiled potatoes
Glycemic Index vs. Glycemic Load
The GI only assesses the quality of carbohydrates, not the actual amount consumed. That is why the glycemic load (GL) is often more meaningful: it also takes portion size into account and provides a more realistic picture of the effect on blood sugar. For example, watermelon has a high GI, but a low glycemic load due to its high water content.
Blood Sugar, Energy, and Mood
Significant blood sugar fluctuations after eating—such as those triggered by high-glycemic foods—can lead to energy crashes, cravings, and mood swings. A diet with a low to moderate GI promotes more stable insulin levels and thus more consistent energy and concentration throughout the day. If you’d like to learn more about the connection between habits and well-being, you’ll find helpful insights in the article “Changing Habits.”
Does the preparation influence the GI of a food?
Yes, considerably. Pasta al dente has a lower GI than soft-boiled pasta. Boiled and then cooled potatoes contain more resistant starch and have a lower GI than freshly cooked potatoes. The ripeness of fruit also plays a role: ripe bananas have a higher GI than green bananas.
Should I only eat foods with a low GI?
Not necessarily. The glycemic index is a useful concept, but not an absolute rule. In the context of a mixed meal - i.e. with fat, protein and fiber - the impact of a high-glycemic food on blood sugar decreases significantly. Overall, a diet should be balanced, varied and enjoyable.