1 June 2010

GI Update

GI Q&A with Prof Jennie Brand-Miller


‘Are you better off drinking a small glass of fruit juice than a non-diet soft drink, cordial or sports drink?
Fruit juices have a low GI in most cases (40–50) and they contribute valuable micronutrients that you won't find in alternative beverages. Some fruit juices are not low GI, e.g. Ocean Spray cranberry juice/drinks, which are around 60. Most non-diet soft drinks are in the GI range of 60–70. Sports drinks can be 70–80. A small glass of fruit juice is probably better than no fruit at all, but best not to make it a daily habit.

‘Does the high amount of fructose in juice have any effect on the release of glucose?’
When it comes to any sugary product (natural or otherwise), you have usually have a mixture of sucrose, glucose and fructose. Sucrose is digested quite quickly to glucose plus fructose before absorption. While glucose is generally absorbed rapidly, it can be slowed by acidic solutions (e.g. all fruits are acidic). Fructose absorption is a much slower process and doesn’t raise glycemia anyway. The high proportion of fructose in fruit and fruit juice is one reason why they have a low GI. But it’s not the only reason. Very large amounts of fructose (70g a day or more) from any source can have adverse effects on blood lipids (fats). The old adage applies: enjoy in moderation.

Fruit juice
Credit: The Low GI Family Cookbook
Photograph by Ian Hofstetter

‘Are there any advantages to drinking fruit juices, or should we opt for whole fruit?’
Opt for whole fruit if you want to feel fuller (satiated) for a longer time. But as long as people limit themselves to one small glass a day, 100% fruit juice can be part of a healthy diet. I can’t think of any advantage of drinking fruit juices (I avoid them myself). It’s much more satiating to eat the same portion as the whole fruit. But I'm pragmatic too ... if there’s no fruit on hand, then fruit juice is better than no fruit, and superior to a soft drink.

Bear in mind that some researchers believe that sugars in solution (whether soft drinks or fruit juice) bypass the satiety centre in the brain, i.e. we don't register them properly and therefore don’t take their calories into proper account. I’d like to see more research on this question. Mother’s milk is a solution of 7% sugar (ie milk sugar = lactose) but babies seem to grow at the right rate

New GI values with Fiona Atkinson
Savoury snacks
Many of us like to nibble on a savoury snack occasionally. But these products (like potato crisps and burger rings etc) are usually high in fat and sodium and tend to have high GI values too. Here at SUGiRS we have just tested Arnott's ‘baked not fried’ Barbecue Shapes. They are a very popular range of savoury crackers here in Australia (about 44 million packets sold every year they say). Here’s what we found.

  • A 25 g serving (about 10 pieces) of Barbecue Shapes (GI 48) provides around 546kJ (130 calories), 6g fat (incl nearly 3g sat fat), 16g carbs and just under 1g fibre and 188mg sodium.
GI testing by an accredited laboratory
North America

Dr Alexandra Jenkins
Glycemic Index Laboratories
36 Lombard Street, Suite 100
Toronto, Ontario M5C 2X3 Canada
Phone +1 416 861 0506
Email info@gilabs.com
Web http://www.gilabs.com/

Fiona Atkinson


Research Manager, Sydney University Glycemic Index Research Service (SUGiRS)
Human Nutrition Unit, School of Molecular and Microbial Biosciences
Sydney University
NSW 2006 Australia
Phone + 61 2 9351 6018
Fax: + 61 2 9351 6022
Email sugirs@mmb.usyd.edu.au
Web http://www.glycemicindex.com/

See The New Glucose Revolution on YouTube