What is Glycemic Index?


Foods and drinks provide fuel for our body in the form of carbohydrates, fat, protein and alcohol. The carbohydrates are the preferred fuel source for the body. The Glycemic Index (GI) is a value assigned to a particular food to classify foods and drinks according to how rapidly they raise the blood glucose level of the blood. It has replaced the earlier approach of classifying carbohydrates as either ‘simple’ or ‘complex’. Carbohydrates containing foods include bread, breakfast cereals, rice, pasta, legumes, corn, potato, fruit, milk, yoghurt, sugar, biscuits, and cakes.

The Glycemic Index (GI)

The glycemic index (GI) is a scale on which carbohydrate-containing foods are rated. The carbohydrate-containing foods are ranked on glycemic index scale based on their influence on blood sugar levels over a period of time or typically two hours.

Foods containing carbohydrates are compared with glucose or white bread as a reference food, which has been given a GI score of 100. The GI compares foods that have the same amount of carbohydrate, gram for gram. Carbohydrates that are digested fast and release their glucose quickly into the blood have a higher glycemic index i.e. GI of more than 70.

Carbohydrates that are low on the glycemic index (GI) scale release glucose steadily into the bloodstream since they tend to break down slowly, for example, oats. They have a GI of less than 55. Low GI foods delay digestion due to their slow breakdown and makes one feel fuller for a longer duration.

The blood glucose level is also affected by the amount of carbohydrate food you eat, not only the kind of carbohydrate. So, to understand the effect of a particular food on the blood glucose levels you need to know how quickly the food makes the glucose enter the blood and how much glucose it will deliver. For example, even though whole grain bread has a low GI, it is not advisable for people with diabetes or impaired glucose tolerance to have a large serving as this will increase the total amount of carbohydrate consumption and calories coming from that.

Glycemic load (GL) which is a value that builds on GI, takes into consideration both the GI of the food and the amount of carbohydrates in a portion of food.

Does GI affect weight loss?

A low GI diet has commonly been endorsed as an effective way to help lose weight by controlling blood sugars and increasing satiety levels. However, the scientific evidence is mixed with inconsistent findings. But, a diet including low GI foods may help prevent conditions like diabetes and heart disease.

For any weight loss, the nutritional quality of the diet is also important instead of focusing just on the GI of foods.

Does GI have an effect on exercise?

Manipulating the GI of meals can help in optimizing the availability of carbohydrates for exercise – especially endurance based activities of moderate intensity. Eating low GI foods four hours before endurance events, such as long-distance running may improve endurance or performance. It is thought that the meal will have left your stomach before you start the event, but remains in your small intestine releasing energy for a few hours afterwards. Many studies show that eating carbohydrate before exercise has a positive impact on performance. However, low GI foods often have a high fiber content in them. So, while some athletes’ have stomachs that can tolerate anything there are a few who experience gastric distress with such high fiber foods. A sports nutritionist will be able to help with the foods that suit each person.

However, during long-distance events drinks with a high GI are consumed as they are easily digested and absorbed to supply energy rapidly. On the other hand, high GI foods are recommended during the first 24 hours of recovery after an event to rapidly replenish muscle fuel stores (glycogen).

How does one choose foods?

Some examples of the foods are as follows:

  1. High-GI foods (70 or higher): white rice, white bread, white pasta, doughnuts, potatoes, biscuits and cookies, sugar-sweetened beverages
  2. Medium-GI foods (56-69): fruits like bananas and grapes, whole wheat pasta and spaghetti, raisins and other dried fruits, corn
  3. Low-GI foods (55 and under): oatmeal, peanuts, peas, carrots, beans, most fruits (except those listed above)

The bottom line is that GI scale cannot replace healthy eating completely. It cannot be solely used for the purpose of weight loss. For example, certain high GI foods like sweet potatoes are rich in antioxidants while some low GI foods like nuts in large amounts can increase the intake of fat and calories in the diet. A balanced diet, keeping in mind the importance of physical activity is the key approach to weight loss programs.

However, in people who are pre-diabetic or are suffering from diabetes, the GI scale can work in stabilizing the blood sugar levels along with regular physical activity. This will reduce the risk of developing diabetic complications.