The low-GI diet

Eating low-GI is a key nutrition message that goes hand-in-hand with other healthy eating guidelines such as eat less saturated fats and eat more fruit and vegetables.

The Glycemic Index (GI) was devised about 20 years ago when researchers looked closer at the dietary recommendations for diabetics; which was to eat more complex carbohydrates (starch) because they took longer to process and digest than simple carbohydrates (sugar).

What the researchers discovered was that the effect of a carbohydrate on blood-glucose levels was not determined by the sugar or starch. For example, we now know that the effect chocolate has on blood-glucose is actually lower than potatoes. That doesn't mean chocolate is healthy — but I'll get to that later.

VIEW GALLERY: Easy low-GI swaps

"You get a bell-shaped curve when you eat food containing carbohydrates; the blood-glucose rises and as your body produces insulin it pushes the glucose out of the blood and into tissues, and then you see the blood-glucose level falling." McMillan-Price explains that when eating high GI foods, you get a very high bell curve response with a dramatic drop. With a low-GI food, there is a slower and steadier rise in the blood-glucose level.

How does low-GI promote better health?
"Research has shown that very high glucose levels after meals, called glucose spikes, are damaging to our arteries and various blood vessels, and they promote far too much insulin to be around," explains McMillan-Price.

Eating low-GI foods means you avoid those spikes and dramatic falls in blood-glucose so you get a much steadier stream of energy. You, therefore, reduce your risk of heart disease and other chronic diseases that are implicated by those blood-glucose fluctuations.

How low-GI contributes to weight control
High GI foods are bad for weight control for two reasons, says McMillan-Price. Firstly, the glucose spikes stimulate hunger because you are getting that dramatic drop in glucose, 90 minutes to two hours after eating. By eating low GI foods you feel fuller for longer and are, therefore, not as likely to go searching for snacks every two hours.

Secondly, insulin is a storage hormone that stockpiles nutrients for later use by the body. A high-GI diet causes a lot of insulin to be produced and when you have too much insulin in your body too much of the time, it makes it easier to store fat and harder to burn it.

Applying the low-GI concept to your diet
McMillan-Price says the recommendation is that at least two meals a day should be accompanied by a low-GI food. "It doesn't mean you should never eat high-GI foods, but preferably put most meals together with a low GI food," she says.

However, don't be worried into thinking you need to know the GI value of every food. Healthy foods such as fruits and vegetables, except potatoes, should be eaten daily regardless of their GI. Simply knowing the low, medium and high varieties of the major carbohydrate foods in your diet — breakfast cereals, breads, rice, pasta — and choosing the low-GI ones is sufficient to produce healthy benefits.

If you simply can't go without certain high GI favourites occasionally, like jasmine rice, serve just a small portion and add a low GI alternative, like a lentil dahl. It is also worth considering the content of your plate. Half your plate should be vegetables, and the other half split into two quarters containing protein and low GI carbohydrate.

Now, getting back to the low GI of chocolate, just because something has a low GI doesn't mean you should indulge, says McMillan-Price. "Low-GI has been misunderstood by some people who think it is the be all and end all," she says. "Don't use the GI as the first step in choosing what foods you should be eating. The GI should come after you've looked at whether something is a good food that has low levels of saturated fat and is nutrient-rich … and then the GI becomes a tool to choose which is the best carbohydrate from these sources."

So, it's not necessary to know the GI of a chocolate bar because it's clearly an energy-dense food without many nutrients that is not going to aid weight loss.

What is the GI symbol?
Foods carrying the GI symbol must meet specific nutritional criteria and have their GI measured using the approved method. The program, designed to help consumers choose low-GI foods, is run by the non-profit company Glycemic Index Ltd, whose members are the University of Sydney, Diabetes Australia and the Juvenile Diabetes Research Foundation.

Glycemic Index Ltd explains that when you see the GI Symbol on a food label, you will find the GI value near the nutrition information panel along with the words 'high', 'medium' or 'low'. You will also know that the food meets the program's nutritional criteria, which generally means it is a good nutritional choice for that food group.

The GI table