GI Q&A with Prof Jennie Brand-Miller
'I am curious why high-fibre cereals like Bran Flakes that look so healthy, and everyone assumes are healthy, actually have a high GI?'
Bran Flakes and Raisin Bran are fibre-rich breakfast cereals designed to keep you ‘healthy on the inside’ as they say. But they are high GI and digested in a flash because the production process makes the starch very accessible. It’s the same with most ready-to-eat breakfast cereals you’ll find in the supermarket
Why do these cereals have high GI values? Grinding, milling, flaking, popping and puffing grains radically changes ‘nature’s architecture’ and makes it easier for water to be absorbed and digestive enzymes to attack the food. This is why many foods (including bread) made from fine flours tend to have a high GI value. The larger the particle size, the lower the GI value.
One of the most significant alterations to our food supply came with the introduction, in the mid-19th century, of steel-roller mills. Not only did they make it easier to remove the fibre from cereal grains, but also the particle size of the flour became smaller than ever before. Prior to the 19th century, stone grinding produced quite coarse flours that resulted in slower rates of digestion and absorption.
When starch is consumed in ‘nature’s packaging’ – whole intact grains that have been softened just by soaking and cooking – the food will often have a low GI. For example, cooked pearl barley’s GI value is 25. But not ALWAYS. For example, some barleys have more naturally-occurring viscous beta-glucans (a form of fibre) that creates greater viscosity in the small intestine and physically slows down the digestive processes. It’s hard to know which varieties of barley are low GI unless they have been previously tested. Brown rice often has a surprisingly high GI too. This is because the insoluble fibre around brown rice is not viscous and it’s micro-thin. It’s easy for enzymes to attack the starch in rice because the milling operation has resulted in thousands of minute channels that allow water to hydrate the grain and gelatinise the starch during cooking. Greater gelatinisation of starch means higher GI.
Prof Barry Popkin on the evolution of cornflakes
‘Dr John Harvey Kellogg (1852–1943) was a Seventh-day Adventist who opened a well-known hospital called the Battle Creek Sanitarium. Actually, it was more like a health resort than a hospital. At Battle Creek, for example, Kellogg taught about food preparation, had his clients engage in breathing exercises and marching to promote digestion, and he gave his guests daily enemas and had them consume yogurt afterward … John Kellogg’s first great discovery was cornflakes, the result of experimentation in the 1890s. The sanitarium kitchen’s cooked wheat was exposed to air for a day or more. Then, when running it through rollers, separate flakes were discharged and cereal flakes were born. The breakfast staple became an instant hit at the sanitarium and beyond, as guests would write after their visits to request supplies of their food.
Somewhere along the line this dream changed. The realities of selling cereal globally transformed Kellogg’s into a company that produced a large array of products with refined carbohydrates, added sugars and fats. The original cereals were made only with whole wheat and contained a small number of calories and plenty of fiber. But that was then – at less than 100 calories per serving – and this, at 120–400 calories per serving, is now. The virtuous company that made truly healthy products is a dim memory. Even so, Kellogg’s Post, and other ready-to-eat cereals are a lot healthier than most breakfast alternatives such as bacon, sausages and fried eggs.’
– The World is Fat
And a tip from Michael Pollan …
‘Don’t eat breakfast cereals that change the color of the milk.’
– Food Rules, An eater’s manual
New GI values from North America: low GI juice beverages
Sweetened with organic blue agave nectar, the new Lo-Gly juice beverages provide 140 calories (588 kJ) per 1 cup (8 fl oz/240ml) serving. Each flavour is certified kosher and the beverages were GI tested in North America at Glycemic Index Laboratories in Toronto. They are available in the US and Canada.
- Pomegranate (contains 49% juice) – GI 28 (total carbs per 1 cup/240ml serve: 35g)
- Acai-Blue (contains 57% juice) – GI 31 (total carbs per 1 cup/240ml serve: 34g)
- Pomegranate Mojito (contains 51% juice) – GI 24 (total carbs per 1 cup/240ml serve: 35g)
- Mango Mojito (contains 56% juice) – GI 32 (total carbs per 1 cup/240ml serve: 31g)
New GI values from Fiona Atkinson: Bakers Delight Chia Bread and Rolls
Bakers Delight have combined with The Chia Company to bring two new moderate GI bread products packed with nutritious chia seeds to the market in Australia and New Zealand.
- Chia White Block Loaf GI 63 – 1 slice has 17g available carbohydrate
- Chia White Round Roll GI 63– 1 roll has 31g available carbohydrate
Dietitian Catherine Saxelby looked at chia seeds in GI News back in August 2009 and reported that: ‘Like all seeds, chia seeds are high in fat especially the good fats. At around 30% fat, they’re lower than sesame seeds (50%) or nuts but make up for this with an extraordinarily high level of omega-3 – unusual in the plant world. They have 18% ALA which is around the same as flaxseeds (linseeds) at 22%, making they are one of the richest sources of the plant form of omega-3 called ALA. They are also big on fibre. In fact, at 37% they are an outstanding source of fibre, in particular soluble fibre. And they contain 15% protein – as much as from wheat – plus a variety of vitamins, minerals and trace elements including folate, phosphorus, iron, manganese, copper and potassium. Like almonds and sesame seeds, they have a surprisingly high content of calcium, usually found in dairy foods, but how well this is absorbed is debatable.’
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