Prof Jennie Brand-Miller answers your questions
Prof Jennie Brand-Miller
My mother has been diagnosed with age-related macular degeneration and besides being told to take lutein and zeaxanthin supplements, she was advised to up her leafy green veggie intake and to eat a healthy low GI diet. Can you explain how a low GI diet would benefit your eyes?
Age-related macular degeneration (AMD) affects the central macula of the eye, leaving sufferers with only peripheral vision. The macula is the small yellowish spot in the middle of the retina that provides the greatest visual acuity and colour perception. It’s the macula that lets us to see fine detail and is critical to central vision helping us to recognise faces, drive a car, read a newspaper, or do close handwork. It is now one of the most common causes of blindness among older adults in the Western world and AMD Alliance International estimates that 25–30 million people are affected worldwide.
Researchers from Tufts and Harvard universities were the first to notice the link between GI and vision. They had followed 526 women without previous visual problems from the Nurses Health Study for ten years. At regular intervals, they assessed the nurses’ diets using a food frequency questionnaire. They found that when total carbohydrate intake was constant, consuming a high GI diet was associated with a doubling of the risk of developing AMD.
Similarly, Professor Paul Mitchell, the lead researcher of the Blue Mountains Eye Study in New South Wales, and his colleagues found that a high GI diet, but not a high carbohydrate diet, was linked to an almost 80 per cent higher risk of having age-related macular degeneration within the 10 years of the study. They also found the incidence of cataracts was higher among elderly people who chose a high GI diet.
Why the link between GI and vision? Well, the retina has among the highest supplies of blood and nutrients, including glucose, and is dependent on adequate glucose delivery from the circulation to maintain its function. Because glucose stores in the retina are negligible and there are no glucose transporters in the cell membrane, it appears that glucose levels in the retina reflect whatever level is found in the blood. High levels spell trouble because excessive uptake produces high reactive charged particles called free radicals that damage all the machinery inside the cell.
Although ‘observational’ data like these studies cannot establish that the observed association is ‘cause-and-effect’, they indicate a new direction for further studies.
GI testing by an accredited laboratory
Dr Alexandra Jenkins
Glycemic Index Laboratories
20 Victoria Street, Suite 300
Toronto, Ontario M5C 298 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