What’s a low GI diet and does it help with weight loss?

Low GI isn’t just another buzzword – it can be a really useful nutrition tool.

However, understanding low GI foods requires a quick science lesson. Basically, the glycemic index (AKA, GI) ranks carbs on how they impact blood glucose levels. “Carbs that have a low GI are digested, absorbed and metabolised more slowly,” says nutritionist Shannon Young. This means a lower and slower rise in blood glucose levels.

The GI scale goes from zero to 100. Low GI foods have a rank of 55 or less. Many fruits and vegetables, beans, minimally processed grains, pasta, low-fat dairy foods and nuts fall into this category. Moderate GI foods have a rank of 56-69. This includes white and sweet potatoes, corn, white rice, couscous and some breakfast cereals. High GI foods have a GI of 70 or more. Foods like white bread, rice cakes, crackers, bagels, cakes, doughnuts, croissants and many packaged breakfast cereals are in this category.

The way a food is prepared can also impact its GI rank. Foods that have been cooked and then cooled can have a lower GI – potatoes are one example. Fat, protein, soluble fiber, fructose and lactose can lower a food’s glycemic response. The ripeness of a food can also alter the GI. For example, an unripe banana may have a GI of 30, while a ripe one can have a GI of 51. Also, if you consume a low GI food with a high GI food, it can create an intermediate GI. That’s just a few of the ways the GI can change!

Can a low GI diet help you lose weight?

The short answer is: yes, it can be a good part of your weight loss toolkit. “A low-glycemic diet can help you control your weight by minimising spikes in your blood sugar and insulin levels,” says Shannon.

“Consuming lower GI and higher protein foods may also have an increased satiating effect,” she adds. “This is related to their slower rate of digestion and absorption. They stay in the gut longer and reach lower parts of the small intestine, increasing satiety hormones making you feel fuller for longer. However, more research is needed to determine whether low GI diets are effective for long-term weight loss.”

More broadly, GI can help you make good food substitution choices. “For example, you might swap in low GI rolled oats instead of higher GI cornflakes or eat grainy bread instead of high GI white bread,” Shannon explains.

However, Shannon warns that the GI has some limitations. “It’s not always necessary to choose all low GI foods. There is room in a healthy diet for moderate to high GI foods and many of these foods can provide important sources of nutrients. A food’s GI ranking does not always reflect its overall healthiness.”

It’s also important to note that GI ranking only applies to carbs, so many foods do not have a GI. That includes proteins like beef, chicken and fish, as well as many vegetables, nuts, seeds and the like.

What about low GI, high protein diets like the CSIRO Total Wellbeing diet?

Many popular diets, such as the CSIRO Total Wellbeing Diet, promote a high protein, low GI style eating plan – and for good reason.

“It is generally accepted that adding protein to higher GI foods reduces the glycemic response,” says Shannon. “Pairing higher GI foods with protein can slow the rate at which the stomach empties and slow the rate of digestion, resulting in a lower GI. Protein also helps decrease appetite and promote feelings of fullness long after meals.” This means you stay satisfied, so you’re not reaching for the snack drawer.

A low GI diet can have other health benefits

According to Shannon, “Low glycemic diets have been linked to reduced risks for cancer, heart disease and other conditions.”

Eating foods with a low GI can also help people with diabetes control their blood glucose levels. According to Nutrition Australia, eating moderate amounts of low GI carbohydrate foods regularly over the day will help maintain consistent blood glucose levels. It’s important to note, however, that GI numbers are a guide only – individual foods do not have the same response in all people with diabetes. It’s critical to consult your own healthcare professional to create a plan that works for you.

In short, it helps to think of low GI as a nutrition tool, rather than as an all-encompassing diet. Incorporating low GI foods can give you the sustained energy that you need to truly thrive.