A recently published review of scientific evidence reports that consuming a high GI diet (GI 60) for five years or more may increase the risk of breast cancer by 8% compared with a low GI diet (GI 45). With the average Australian diet consisting of far too many high GI foods, this is a major cause for concern. Current Australian data indicates 1 in 9 women will be diagnosed with breast cancer before the age of 85, with the disease accounting for around 1 in 4 cases of all cancers in women.
While there are a large number of uncontrollable risk factors for breast cancer such as genetics, menopause and family history, there are also a number of lifestyle-related risk factors that you can change. Factors which increase the risk of developing breast cancer include:
Excessive alcohol consumption
High processed meat consumption
Being overweight or obese.
Australia's leading GI researcher, Professor Jennie Brand-Miller from the University of Sydney, believes a low GI diet reduces the risk of breastcancer for two reasons. "Consuming a low GI diet reduces both glucose and insulin levels, helping us to burn more fat and avoid weight gain over the longer term. Insulin is a hormone that drives cell growth and multiplication. If you have a mutated cell, then it grows faster and bigger under the influence ofhigh insulin.
"Secondly, some breast cancer cells positively thrive onoestrogen. Body fat manufactures and releases oestrogen which can aid the spread of breast cancer. Overweight women are more likely to have breast cancer for this reason."
A low GI diet reduces accumulation of body fat and insulin levels thus reducing the risk of many health problems including:
Heart disease and stroke
Type 2 diabetes
Other lifestyle related diseases.
Choosing low GI carbohydrates is the secret to long-term health. The easiest way to find healthy low GI choices is to look for foods in the supermarket with the low GI symbol. Foods with this symbol have not only had their GI tested at an accredited lab, but they must also have met category specific nutrient criteria for calories/kilojoules, total and saturated fat, sodium (salt) and where appropriate, fibre and calcium.
The GI Symbol Program makes it easy for everybody to put nutritious, low GI food choices into their shopping trolley and reap the long-term health benefits of enjoying a low GI diet.
To find out more about the GI Symbol Program, the Glycemic Index Foundation and low GI eating, log onto www.gisymbol.com. To view GI values for over 1000 foods on Australian supermarket shelves go to www.glycemicindex.com
Question: Can you talk about the correlation between a high GI diet and increased risk of breast cancer and other diseases?
Professor Jennie Brown-Miller: The large study we conducted recently that attracted attention showed that there was an association between diets with a high glycemic index and future risk of developing breast cancer in women; that doesn't prove there is a connection but there is an association. There is a plausible mechanism; we know that blood glucose stimulates a lot of insulin secretion (insulin is a hormone that makes cells multiply) and if you have a mutant cell, like a breast cancer cell, then there is a possibility that a diet that produces a lot of insulin secretion will encourage the multiplication of the breast cancer cell and not just breast cancer, any cancer.
Insulin is recognised as a master hormone that encourages growth full stop. When you have high levels of insulin in your blood you often have weight control issues, as well.
Question: What foods and drinks have a high GI level and we therefore need to moderate?
Professor Jennie Brown-Miller: The surprise is that many of the modern starchy foods that we think are very healthy are some of the foods that have the highest GI levels such as most breads, breakfast cereals, rice and potatoes; on a scale from 0-100 some potatoes have a glycemic level of 100 and that is because their starch is rapidly digested and absorbed. The good news is that within every one of those categories (whether it is bread, breakfast cereals or rice) there are low GI varieties. Women need to make appropriate swaps; they do not need to turn their diet inside out.
Question: How does being overweight also increase a women's chances of developing breast cancer?
Professor Jennie Brown-Miller: This study is independent of weight, even taking weight into account there is an association between a high GI diet and future risk of developing breast cancer.
Question: What types or research has the University of Sydney done in regards to the correlation between GI diets and breast cancer?
Professor Jennie Brown-Miller: We did an early meta-analysis in 2008 which takes lots of small studies and combines them to see if there is an effect which is significant when combining small studies. Many studies are not well designed as they don't have enough people studied to show an effect when the effect is small. In this case the effect is fairly small as on average the risk is only increased by 8% when having a higher vs. lower GI diet. 8% is not a lot but when it comes to breast cancer the problem is it is a common cancer and a small increase in risk affects an awful lot of women; in absolute terms it is important even though the relative risk (the risk of a high GI diet vs. lower GI diet) is quiet small.
In nutrition epidemiology anything that significant and associated with a 10% increased risk is clinically important when it is a common disease, like breast cancer is.
Question: How can we tell if a food has a low GI level?
Professor Jennie Brown-Miller: We've taken the hard work out of it! We have formed a not-for-profit foundation that has a mission to help consumers identify healthy low GI foods. We have a symbol on foods that belong to the program, the foods are not only low GI they are nutritious in their food category. The symbol is a circle and is coloured green and blue. The symbol is found on common foods in the supermarket, the best example is Burgen bread. The symbol is also on breakfast cereals, rice and cous cous that are low GI. The only low GI variety of potatoes on the Australian market is called Carisma; this variety of potato is selling like crazy.
Visit the websitewww.gisymbol.com.
Question: I use the Carisma variety of potatoes and they taste the same, if not better as other potatoes and I have been able to replicate all potato dishes with the variety.
Professor Jennie Brown-Miller: That's good to hear. The company that owns the seed stock for Carisma potatoes has gone worldwide because everybody loves it. Within two years they think half the potatoes grown, in America, will be Carisma potatoes.
Interview by Brooke Hunter
Photo: Gavin Jowitt