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Glycaemic index (or GI for short) is a way of ‘ranking’ carbohydrate foods according to the speed at which they cause our blood glucose levels to rise and fall. Carbohydrate foods are those containing starches (including breads, cereals, grains, pasta, noodles, legumes and starchy vegetables) and sugars (both added sugars and the natural sugars in fruit and some dairy products).
When we eat, the carbohydrates in food are broken down during digestion into glucose and provide the body with energy. But different carbs have different effects on our blood glucose levels. Some are more quickly digested and absorbed (which we refer to as high GI), while others break down slowly, gradually releasing glucose into the bloodstream (known as low GI).
Many studies have looked at the role of low GI diets for people with and at risk of diabetes. Overall, the research shows that, compared to higher GI diets, low GI diets can help to manage blood glucose levels – lowering both fasting glucose levels and HbA1c (a measure of average glucose levels over the past 2-3 months). A low GI diet may also help to lower blood fats and assist with weight management.
Changing to a low GI diet isn’t difficult. You don’t need to cut out any foods or food groups, just make different choices. For example, you could:
Switch puffed and flaked breakfast cereals for traditional or steel-cut rolled oats or natural muesli.
Swap white, wholemeal and light rye bread for dense wholegrain bread (one with lots of intact grains).
Try wholegrains such as pearl barley, quinoa, freekeh and burghul in place of rice, or choose lower GI varieties of rice such as basmati or Doongara (Sun Rice Low GI rice).
Include legumes (such as lentils, chickpeas and dried or canned beans) in your meals regularly – add them to soups, stews and salads, make them into dips or use white beans in place of potato in mash.
Choose lower GI varieties of fruit including apples, pears, citrus fruits, berries and stone fruit like peaches and nectarines.
Snack on fresh fruit, nuts, natural yoghurt, hummus and vegetable sticks and roasted chickpeas in place of processed snack foods such as chips, sweet biscuits and most cracker biscuits.
Start by focusing on the carbohydrate foods that make up a regular part of your diet, and switching these to lower GI choices. Even switching half of the carbs you eat in a day from high to low GI choices or including one low GI food at each meal is of benefit.
It’s not always just about GI
While there are benefits to choosing lower GI foods, it’s important to keep in mind that GI shouldn’t be used in isolation when making healthy food choices. You may notice that some low GI foods are high in saturated fat and added sugar (e.g. chocolate and ice-cream), while some high GI foods may still be good choices because they are nutritious and relatively low in energy and carbohydrate (e.g. watermelon). So, consider whether a food is a healthy choice first and then go for the lower GI options, rather than choosing foods based on GI alone.
It’s also important to use GI alongside other healthy eating recommendation for diabetes including:
Spreading carbohydrate intake over the day and having similar amounts from day to day, or matching your carb intake to insulin doses.
Eating plenty of fibre from fruits, vegetables and wholegrain breads and cereals.
Limiting intake of saturated fats from foods such as fatty and processed meats, butter, cream, cakes, biscuits, pastries, chocolate and fried takeaway foods.
Limiting added sugars.
How do I know which foods have a low GI?
Lower GI foods include legumes (lentils, chickpeas and canned/dried beans), rolled or steel-cut oats, wholegrains such as barley, quinoa, freekeh and burghul, dense wholegrain breads, pasta (not the gluten-free varieties), sweetcorn, many fruits, and dairy products such as plain milk and yoghurt. Unfortunately, not all foods have been GI tested due to the time and cost involved, but when choosing packaged foods, you can look for the Glycaemic Index Foundation’s Low GI Certified symbol. As well as certifying that a food is low GI (meaning it has been tested by approved methods), it must also be an overall healthy choice within its category, having to meet criteria for energy, total and saturated fat, sodium, and where appropriate, fibre and calcium
You may have also come across the term glycaemic load (GL) and be wondering how this differs from GI, and which is more important. The overall effect that a food has on blood glucose levels is dependent on both the nature (GI) of the carbohydrate it contains and the amount (the grams of carbs). GL takes both of these factors into account and is calculated by multiplying the GI of the food by the amount of carbohydrate per serve and then dividing by 100. For example, an apple has a GI of 40 and contains 15 grams of carbohydrate so has a GL of 6 (40 x 15)/100.
While foods with a high carbohydrate content and those with higher GI values will generally have the highest GL, this also means that small amounts of a high GI food may have only modest effects on blood glucose levels while large amounts of a low GI food can still raise blood glucose and insulin levels significantly. So, there’s no need to avoid foods that have a high GI but are relatively low in carbohydrate and nutrient-dense – a good example of this would be watermelon. On the other hand, just because a food is low GI, it doesn’t mean you can eat as much as you like, particularly if you are watching your weight or blood glucose levels.
Where can I find out more?
University of Sydney GI Website www.glycemicindex.com
This website explains all about GI and GI testing and includes an advanced food search to allow you to search for the GI value of different foods
GI Symbol Program www.gisymbol.com.au
This website explains all about the GI symbol program, shows you which products carry the certification logo and provides low GI recipes and menu plans
Sydney University GI Newsletter http://ginews.blogspot.com/
To keep up to date on the latest research on GI and carbs, subscribe to the University of Sydney’s GI newsletter.
Please remember, it is important to consult with a doctor or diabetes healthcare professional for personalised advice and guidance on how to manage diabetes.
Remember to always seek advice from your medical practitioner before changing anything about your diabetes management. The above information is not medical advice.
