An update on glycemic index and glycemic load

Guest Post Sally Marchini, Dietitian

As usual there’s been a lot of talk lately about the Glycemic Index (GI) and how it affects us with diabetes. As I hope you know I wrote a series of blogs on the glycemic index – it’s benefits, how to make the change to a low-GI way of eating, and how both quality and quantity of the carbs you choose will make a difference to your glycemic control.  I would encourage you to revisit these blogs to remind yourselves of the points included that will benefit everyone’s health, with or without diabetes, but especially so for those of us with it.

The reason for my further blog on this topic today is that last week I attended a seminar presented by Dr Alan Barclay who is Chief Scientific Officer at the Glycemic Index Foundation, and Head of Research at the Australian Diabetes Council (formerly Diabetes Australia-NSW). He is also co-author of the Diabetes and Pre-diabetes Handbook. The topic of Dr Barclay’s presentation was ‘The Latest Developments in Glycemic Index and Load’ and there were a few key points in there that I thought were worth bringing to your attention. He kindly agreed that I could share it with you as there were some very valid points made to help our understanding of how the GI of food affects us.

So, the following information is taken from Dr Barclay’s presentation with his kind permission to share with you.  I hope you benefit from it as much as I have.

A great starting point was a reminder of the definition of Glycemic Index.  The GI compares equal quantities of available carbohydrate in foods, is a measure of their effect on blood glucose levels in 10+ healthy people over a 2 hour period, and is expressed as a percentage.

The GI Ranking (as I hope you do know since we’re always on the lookout for the low ones) for individual foods looks like this:

• Low = 55 or less
• Moderate = 56-69
• High = 70+

I also liked the example of an apple he provided in his definition of Glycemic Load (GL):

“A function of a food’s glycemic index and its total available carbohydrate content and defined as:

Glycemic Load = GI (%) x Carbohydrate (g)

Using an apple (140g with skin and core):  GI value = 38%; Carbohydrate per serve =15 g

GL = 0.38 x 15 = 6

The GL of a medium sized (140g) apple is 6.  Don’t you love how easy that is to work out??

It’s important to remember that the higher the GL, the greater the elevation in blood glucose AND insulin levels, so it’s worth keeping an eye on.

As already mentioned, both the amount and type of carbs are important predictors of blood glucose levels but something that I hadn’t specifically talked about is that together they account for 90% of the total variability in blood glucose response.

Dr Barclay then ran through a number of studies that demonstrated benefits as outlined in that first blog of mine, including an extra couple worth mentioning here:

• There was Grade A (the best) evidence to show that for those of us at risk of hypoglycaemia, those people who favoured low-GI carbs had significantly fewer hypos than those who didn’t.
• Research demonstrating that low GI foods tip the balance in favour of fat oxidation (meaning you’ll burn fat rather than store it)
• In terms of weight maintenance, one study, a randomised controlled trial called Diogenes, showed that people on a Low-GI higher protein diet were able to maintain their weight loss where all the other ‘diets’ led to weight regain over a 6 month period.

You can read more about this sort of research here if you’re interested.

 

You know of the GI Symbol, but were you aware of what the requirements are to be able to display the symbol on packaging?

• Products must be tested by approved laboratory using the Australian Standard procedure.
• Products must contain greater than or equal to 10g of carbohydrate, or greater than or equal to 80% carbohydrate AND be traditionally served in multiple units of small serve sizes
• Products must meet strict nutrition criteria (all the things we’re looking for with diabetes!):
  • Energy
  • Total and Saturated Fat
  • Sodium
  • Dietary Fibre
  • Calcium

Another part that I thought worth reminding you of was that the University of Sydney publishes an e-newsletter called GI News that you can subscribe to which has great articles and recipes as well as listing the latest foods that have been tested for their GI values.

 

And something for your shopping bag! There’s a booklet that sells for about $12 called the ‘Low GI diet Shopper’s Guide’ that contains the GI values of more than 1000 foods – great to carry with you when you’re doing the weekly shop!  You can buy it from any bookseller, but I saw them in stock at the Australian Diabetes Council in Sydney (for $12) when I was there for Dr Barclays presentation, so I’m guessing they’re also available through other state Diabetes Australia outlets.

If you’re looking for low-GI food ideas, the GI Foundation website not only has a special section for diabetes, but also some great recipes and many other hints and tips including a SWAP calculator to help you find a lower-GI alternative to your favourites.

What a great way to eat well and know that you’re helping to improve your diabetes wellbeing!  Thanks Dr Barclay!

As usual, please let me know if you have any questions or ideas to share.

Sally.

Sally Marchini is owner of her private practice (Marchini Nutrition), has had type 1 diabetes for close to 40 years and coeliac disease for many years too.