GI Q&A with Prof Jennie Brand-Miller
Can you explain why some ‘wholegrains’ have a low GI and others don’t?
Not all ‘wholegrain’ foods are created equal, in fact they can behave quite differently in our bodies depending on the following five key factors that can slow digestion, making them even better-for-you low GI choices.
Starch matters There are two types of starch found in foods – amylose and amylopectin – and the ratio of them in foods can vary considerably. The more amylose a food contains, the less easily the starch is gelatinised and the slower its rate of digestion. This is because amylose is a straight chain molecule, like a string of beads. These tend to line up in rows and form compact clumps. Legumes have lots of amylose as does basmati rice. Amylopectin on the other hand is a string of glucose molecules with lots of branching points, such as you see in some sorts of seaweed. Amylopectin molecules are larger and more open and the starch is easier to gelatinise and digest as in jasmine rice.
Size matters The larger the particle size, the lower the GI. It’s the grinding or milling of cereals that reduces the particle size that makes it easier for water to be absorbed and enzymes to attack during digestion. That is why cereal foods made from fine flours like many breakfast cereals tend to have a high GI value.
Fibre matters Soluble fibres – the gel, gum and often jelly-like components of foods like oats, legumes and apples – can lower your body’s glycemic response to a food because they slow down the time it takes for food to pass through the stomach and small intestine.
Insoluble fibres are dry and bran-like and often referred to as roughage. Insoluble fibres will only lower the GI of a food when they exist in their intact, original form, for example in whole grains of wheat (the kernel). Here they act as a physical barrier, delaying access of digestive enzymes and water to the starch within the cereal grain.
Physical entrapment The fibrous coat around foods like beans, chickpeas, lentils, barley and seeds acts as a physical barrier. It slows down access of the digestive enzymes to the starch inside and thus slowing digestion.
Starch gelatinization The starch in raw food is stored in hard, compact granules that make it difficult to digest. During cooking, water and heat expand these starch granules to different degrees – some actually burst freeing the individual starch molecules inside. If most of the starch granules have swollen and burst during cooking, we say that the starch is fully gelatinised. These swollen granules and free starch molecules are very easy to digest.
New GI values with Fiona Atkinson
Hurrah! A GI value for traditional Chinese pork buns!
The April edition of World Journal of Gastroenterology includes the GI values of 23 popular Chinese traditional foods tested by Prof Wong Heung-sang Stephen and his colleagues in the Chinese University of Hong Kong. The results of this study are also preliminary references on the setup of a GI database for Chinese traditional foods. You can find the GI and GL values of these foods on the database at www.glycemicindex.com
- Low GI: tuna fish bun, egg tart, green bean dessert, Chinese herbal jelly, fried rice vermicelli in Singapore-style, and spring roll
- Moderate GI: baked barbecued pork puff, fried fritter, “mai-lai” cake, “pineapple” bun, fried rice noodles with sliced beef, barbecue pork bun, moon cakes, glutinous rice ball, instant sweet milky bun, and salted meat rice dumpling
- High GI: fried rice in Yangzhou- style, sticky rice wrapped in lotus leaf, steamed glutinous rice roll, jam and peanut butter toast, plain steamed vermicelli roll, red bean dessert, and frozen sweet milky bun
Correspondence to: Stephen Heung-sang Wong, email: firstname.lastname@example.org
The Shopper’s Guide to GI Values 2010 Giveaway
Find the GI values of your favourite foods and brands at a glance IN THE 2010 EDITION OF The shopper’s Guide to GI Values. It has the GI values of over 1000 foods plus special sections on sugars and sweeteners, gluten-free eating, and dining out.
The Australian Edition Giveaway is now closed. Thanks for all your support, we had over 400 entries. We will post the names of the Australian winners below in the next couple of days.
The US Edition Giveaway is now closed. Thanks for all your support, we had over 500 entries. We will post the names of the American winners below in the next couple of days.
GI testing by an accredited laboratory
Dr Alexandra Jenkins
Glycemic Index Laboratories
36 Lombard Street, Suite 100
Toronto, Ontario M5C 2X3 Canada
Phone +1 416 861 0506
Research Manager, Sydney University Glycemic Index Research Service (SUGiRS)
Human Nutrition Unit, School of Molecular and Microbial Biosciences
NSW 2006 Australia
Phone + 61 2 9351 6018
Fax: + 61 2 9351 6022
See The New Glucose Revolution on YouTube