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.

5 Comments

  1. Melinda on February 24, 2014 at 11:47 am

    Thanks for this article Sally, most interesting as usual, and as usual i have a question:

    “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 response.”

    That’s a fascinating statistic but upon further reflection, I don’t have a clue what it really means. I understand the words of course but what exactly is “blood response”? and does this apply to non-diabetics/t2/t1diabetics, is it applicable at an individual or population level and how did they quantify it? I’d be most interested in any further info. Cheers

  2. Sue on February 24, 2014 at 3:42 pm

    Great questions Melinda, I’d like answers to those too!
    Thankyou Sally for the reminder about calculating glycaemic load. I first read te New Glucose Revolution about 10 or 12 years ago, and immediately started trying to get a grip on the GI of different foods, and observing what happened to my bgls. But at the time I thought calculating the glycaemic load was just too much number crunching.
    Instead, I’ve thought of the GI in a more conceptual way – I make the carb base of my meal low GI, and to add a very small amount of high GI is then ok. I have also found that a meal with too low a GI means a hypo later, because the carbs are slower than the short-acting insulin, but for some reason dieticians and the GI people don’t mention this. Hence the value of Melinda’s question.
    Cheers,
    Sue.

  3. Sally on February 24, 2014 at 7:25 pm

    Thanks for your comments Melinda and Sue 🙂

    The reason you don’t have a clue as to what it means Mel, is that I accidentally left a word out!! It should read “90% of the total variability in blood glucose response”. Thanks for picking that up for me and I’ve made the change in the blog.

    Dr Alan Barclay kindly confirmed for me that “All of this research is based on studies of small groups of people. If we were to say population level, then we would be talking about people with diabetes (type 1 & 2).”

    The particular study was called ‘Food insulin index: physiologic basis for predicting insulin demand evoked by composite meals’ by Jiansong Bao, Vanessa de Jong, Fiona Atkinson, Peter Petocz, and Jennie C Brand-Miller. Published in the Am J Clin Nutr 2009;90:986.

    And Sue, it’s tricky for me as a dietitian to comment on dietitians not talking about low-GI foods causing hypos with fast acting insulin as I have type 1 myself so understand the issue well. I know the presentations that Medtronic provide cover this issue closely relating to the functions on their pump allowing us with type 1 to deal with this issue. So maybe it depends on the experiences of the dietitian concerned – I know many highly experienced dietitians who work in diabetes, and this sort of information is certainly known by them.

    Hoping this answers your questions Ladies. Best wishes, Sally 🙂

  4. Carolyn on February 25, 2014 at 4:27 am

    Thanks for this article which will be helpful to me

    • Helen-Edwards on March 3, 2014 at 9:28 am

      you are more than welcome Carolyn

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