The Glycaemic Index (GI) is a relative ranking of carbohydrate in foods according to how they affect blood glucose levels.
The quicker the conversion from carbohydrate to glucose the higher the GI rating of the food. High GI foods cause a steep rise in blood glucose levels therefore release energy quickly, whereas low GI foods are absorbed into the bloodstream slower giving a more consistent and steady release of energy over a longer period.
Foods considered to be high GI will rank as 70 or more, medium GI foods will rank as 56 - 69 and low GI foods have an index of 55 or less.
What affects GI?
- Fibre content - wholegrains have more fibre giving a lower GI
- Fat content - fat lowers GI
- Protein content - protein lowers GI
- Cooking methods - shorter cooking times (al dente) reduces GI
- Processing methods - refined carbs have natural fibre removed, for example white rice has had the husk removed whilst brown rice has only the outermost layer of the husk removed, retaining fibre
- Ripeness of fruit or vegetables "“ over-ripe foods have a higher GI
Should I follow a low GI diet?
It is important to know that not all low(er) GI foods are the healthiest options, and vice versa, some high GI foods are what would be considered a benefit to our diet. For example milk chocolate as a GI value of 43 and an apple 38. We know which we should be eating more of, so it`s important to factor this in! Chocolate has a lower GI value than you may think due to its fat content. Also as each individual food has its own GI value when put together with different foods as a meal this will change so it is important not to get too fixated on each food. It is important to balance meals so that they contain sufficient fruit and vegetables, wholegrains, lean protein sources (lean meats and poultry, fish, eggs, beans and pulses) and are lower in nutrients associated with ill health - salt, sugar and saturated fat. So absolutely include more of the lower GI foods which are great for our health
Glycaemic Index and Diabetes
For people with diabetes, specifically type 2, low GI foods can assist with regulating blood glucose (aka blood sugar) levels on a day to day basis. However taking into account the amount of carbohydrate consumed is the number one dietary factor when managing type 2 diabetes, with portion control playing an important role in this. Speak to your healthcare professional for more advice.
Top Tips on Maintaining Blood Sugar Levels
- Choose porridge, no added sugar muesli or a wholegrain breakfast cereal such as Weetabix
- Eat regular meals to maintain consistent blood glucose levels
- Try to get a balance of protein, vegetables and carbohydrates in each meal
- Between meals try snacking on healthy, low GI foods like nuts, seeds and fruits
- Use food labels to check fat, saturated fat and sugar content as well as recommended portion size
- Eat the skin on jacket potatoes for extra fibre and give sweet potatoes a go for something different
- Basmati, brown or easy cook rice have the lowest GI values, or try a different grain like bulgur wheat or quinoa
- Where possible eat wholegrain varieties of carbohydrate
Article written by Rees Bramwell, ANutr.
Aston et al. 2010. Developing a methodology for assigning glycaemic index values to foods consumed across Europe. Obesity Review.
Diabetes UK. Glycaemic Index and Diabetes. Accessed April 2018 at www.diabetes.org.uk/guide-to-diabetes/enjoy-food/carbohydrates-and-diabetes/glycaemic-index-and-diabetes
Food Standards Agency, McCance & Widdowson`s The Composition of Foods, 2002.
NICE, Type 2 Diabetes in Adults, 2017.
Above graph sourced from The University of Sydney. 2017. About Glycemic Index. Accessed April 2018 at www.glycemicindex.com/about.php