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Glycaemic Index and a low GI diet

The glycaemic index (GI) tells us whether a food raises blood glucose levels quickly, moderately or slowly. Different carbohydrates are digested and absorbed at different rates, and GI is a ranking of how quickly each carbohydrate-based food and drink makes blood glucose levels rise after eating them. Therefore, particularly useful if you are diabetic and need to have manage your blood sugar levels carefully.

Glycaemic Index (GI)

GI is a measure of the effects of a foods carbohydrate component on blood sugar levels. Carbohydrates that break down quickly during digestion and rapidly release glucose into the bloodstream are characterised as having a high GI value, whereas carbohydrates that are broken down slowly and release glucose into the bloodstream in a more gradual manner are characterised as having a low GI value.

  • Low GI = <55

  • Medium GI = 56-69

  • High GI = >70

Important considerations with a low GI diet

The GI value relates to the food eaten on its own and in practice we usually eat foods in combination as meals. Bread, for example is usually eaten with butter or margarine, and potatoes could be eaten with meat and vegetables.An additional problem is that GI compares the glycaemic effect of an amount of food containing 50g of carbohydrate but in real life we eat different amounts of food containing different amounts of carbohydrate. Thus, the amount of carbohydrate you eat has a bigger effect on blood glucose levels than GI alone.

Glycaemic Load (GL)

Glycemic Load takes into account a foods GI value and a standardised 100g portion size and is calcuated as GL = GI x available CHO in a 100g serving / 100. Therefore the GL takes into account the amount of carbohydrate consumed and is a more accurate measure of the impact of a food on blood sugars. As a general rule, foods with a low GL usually have a low GI and those with a medium to high GL value almost always have a very high GI value.

  • Low GL = <10

  • Medium GL = 11-19

  • High GL = >20

Nonetheless, it does not mean all foods with a high GI are unhealthy and setting yourself a restrictive diet can result in you not obtaining all the nutrients your require. There are many factors to take into account e.g. combining your carbohydrate foods sources with protein, healthy fats and adequate levels of fibre, the time intervals between your meals.

Click here for a low GI breakfast recipe idea

If you have any concerns over your diet or managing your sugar levels we are here to help. Contact us at

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