Glycemic index

As we covered last week, not all sugar (carbohydrate) is equal. Part of this story relates to how different sources of carbohydrate in food influence our blood glucose level. The method by which this is determined is called the Glycemic Index.

A display of foods - cereal, sugar, milk, lentils and fruit

Glycemic Index and health

The glycemic index (GI) ranks a food containing carbohydrate according to how quickly blood glucose levels rise after eating that food. The GI system allocates a ranking of 0–100 to foods. A high GI food is ranked 70 or more, a medium GI is 56–69 and a low GI is 55 or less.

Including foods with a low GI in your regular eating pattern has several health benefits through reducing body fat and maintaining a healthier body weight, and lowering the risk of developing type 2 diabetes, diabetes complications and heart disease.

Low GI

  • All varieties of legumes and lentils
  • Multigrain, traditional sourdough and rye bread
  • Brown, wild and basmati rice
  • Mixed grain porridge
  • Nicola and sweet potato
  • Apples, apricots and oranges
  • Cows milk and yoghurt

Medium GI

  • White and wholemeal bread
  • Short grain rice such as aborio
  • Rice noodles
  • Pontiac potato
  • Banana, mango and pineapple

 High GI

  • Puffed rice breakfast cereals
  • Rice cakes
  • White potatoes
  • Canteloupe (rockmelon) and watermelon

Additional food examples can be found by searching the University of Sydney GI research library.

GI and nutritional quality

The GI is not a ranking system for overall nutritional quality of foods. A highly processed, high glucose food or drink can have a low or medium GI, but is devoid of fibre, vitamins, minerals and phytonutrients (including antioxidants). These have essential roles in maintaining good health and preventing lifestyle related diseases such as heart disease and diabetes. To get the full benefit of the GI system eat mostly wholefoods with low to medium GIs.

A benefit of the GI approach is that by adding a food with a low GI (kidney beans) to a meal that contains a higher GI food (white potatoes) the overall GI of the meal will be reduced.

This highlights the synergistic effect of foods and that no single food provides a magic bullet.

In general the more refined a food is the higher the GI becomes. For example wholegrain flour that contains kibble (heavier denser flour) is lower in GI than fine white flour. Other components in food also affect GI. Traditional sour dough bread takes two days to make. The acid resulting from the rising process lowers the GI of the bread. This process also toughens the structure of the bread, making it chewier in texture and lowering the GI.

The GI symbol has been introduced to assist in the selection of processed foods that also meet nutritional guidelines for key nutrients such as saturated fat, fibre and added sugar.

Take home message

The GI assists us in choosing foods that decrease the rise in our blood sugar level and aid satiety (make us feel satisfied for longer). These two factors help support good health when the total diet is considered. For people with diabetes I suggest monitoring any changes to your intake of carbohydrate foods by keeping a food diary and recording your blood sugar levels after meals. If you are seeking sustained energy and mental clarity from making dietary changes, then I encourage you to remain mindful of how and what you eat affects you. A food diary helps here too!

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