You’ve probably heard of the GI (Glycemic Index) and you may know that it’s better to choose lower GI foods. But do you know exactly what the GI of a food means, which foods are lower GI and how choosing lower GI foods can help you to manage your weight? For answers to these questions, read on.
So what exactly is the GI?
The glycemic index (or GI for short) is essentially a way of ‘ranking’ carbohydrate foods according to the speed at which they cause our blood glucose levels to rise and fall. When we eat, carbs 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).
The Glycemic Index ranks foods (on a scale from 0 to 100) according to the extent to which they raise blood glucose levels after eating compared to glucose (which is given a GI of 100). Foods with a GI value of 55 or less are considered low GI, foods with a GI of 56-69 are considered moderate GI and foods with a GI of 70 or above are considered high GI.
Why go low GI?
The smaller rise in blood glucose levels after meals containing lower GI foods is particularly important if you are looking at weight management
Low GI diets may also:
- Reduce the risk of developing type 2 diabetes
- Lower ‘bad’ LDL cholesterol levels and reduce heart disease risk
- Reduce the risk of certain cancers including endometrial, breast, colon and ovarian cancer
- Assist with weight management by keeping you fuller for longer and reducing insulin levels, which, in turn, helps you to burn fat.
What’s more, a low GI diet fits very well with the general healthy eating recommendations we know can help with weight and optimising our health, including eating more fibre, fruits, vegetables and wholegrain breads and cereals.
But that said…..it’s not just about GI
It is 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 (e.g. chocolates, pizza, and potato chips), 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, when using GI, it should be used to supplement other healthy eating guidelines including eating plenty of fruits, vegetables and wholegrain breads and cereals, replacing saturated fats with unsaturated fats (e.g. from olive oil, avocado, nuts, seeds and fish) and limiting foods high in added sugar.
And portion sizes still matter. If you eat a large amount of a low GI food, you will still put on excess weight.
What influences the GI of a food?
The GI of a food is affected by many different factors including:
- The type of sugar in the food. For example, fructose, glucose, lactose and maltose all have different GI values.
- The type of starch in the food including the proportion of amylose to amylopectin and the gelatinisation of the starch. The more amylose a food contains, the less easily the starch is gelatinised (due to the structure of the glucose molecules) and the slower its rate of digestion will be. For example, Basmati rice and legumes have a higher proportion of amylose and therefore have a lower GI. Wheat flour and short grain rice have a higher proportion of amylopectin, which is more easily digested, and therefore have a higher GI.
- The type of fibre – soluble fibres are more slowly digested than insoluble fibres. Foods high in soluble fibre include oats, barley and legumes.
- How a food is prepared – processing, cooking, pureeing and grinding all increase the GI of a food. For example, grains in their whole, intact form generally have a low GI whereas when they are puffed and flaked (such as most breakfast cereals and cracker biscuits) or ground into flour (for example in white or wholemeal bread) they have a high GI.
- The ripeness of fruit. This is particularly the case for bananas which have a higher GI the riper they are.
- The presence of fat or protein slows down the rate of stomach emptying and therefore slows down starch digestion, as do acids in food such as vinegar and lemon juice.
How to know which foods have a low GI
One problem with GI is that it isn’t simple to measure – it is tested in real people and can’t be determined by the composition of the food. This means that many foods haven’t been tested yet, although the number is increasing all the time.
When it comes to packaged foods, your best bet is to look out for the Glycemic Index Foundation’s Low GI Certified symbol. As well as certifying that a food is low GI (as 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 can also use the Sydney University GI Food database to see if a particular food has been tested and what it’s GI is.
Simple swaps
Even without the symbol, there are some easy changes you can make to switch some of your everyday carb choices to lower GI options.
| Higher GI Food | Low GI Alternative |
| White, wholemeal or light rye breads; most gluten-free breads | Bread containing lots of whole grains (eg. Burgen® and Vogels® breads, Bakers Delight Cape Seed or Wholemeal Country Grain, Tip-Top 9 Grain™) or sourdough and pumpernickel breads |
| Puffed and flaked breakfast cereals, quick oats | Unrefined cereals such as steel-cut rolled oats or natural muesli or a low GI processed cereal such as those containing barley or psyllium husks (e.g. Kelloggs® All-Bran®, Goodness Superfoods® Digestive and Heart cereals, Kelloggs® Guardian®, Vogels® Ultrabran) |
| Plain biscuits or crackers, corn thins, rice cakes | Biscuits made with dried fruit, oats and wholegrains (eg. Arnotts™ Snackright Fruit Slice, Vitaweat Lunch Slices™ Soy, Linseed & Sesame) |
| Most varieties of potato | Substitute with Carisma™ potatoes or corn; make mashed potato with half cannelleni beans |
| Many varieties of rice, including jasmine and Calrose | Try longer grain varieties such as Basmati, Doongara (Sun Rice® Low GI White or Low GI Brown rice) or try pearled barley, freekah, quinoa, cracked wheat or noodles instead |
| Most gluten-free pasta | Regular pasta and most noodles (but keep them on the al dente side); Coles Simply Gluten Free Pasta |
| Tropical fruits | Temperate fruits (e.g. apples, pears), citrus fruits, berries, most stone fruits |
| Cakes and muffins | Make them with fruit, rolled oats, rolled barley, oatbran, rice bran, barley bran, psyllium husks, nuts and seeds |
Where can I find out more?
If you want to learn more about GI, the following books and websites are a good place to start
Sydney University GI Newsletter