High-Glycemic Diet May Lead to Blindness
A new study has found that high-glycemic diets, consisting of the type of carbohydrates that most Americans eat, increase the risk for age-related macular degeneration. This disease alters the inner lining of the eye, known as the macula area of the retina, causing thinning, atrophy, and in some cases bleeding. As it progresses, macular degeneration robs people of their central vision—the type of vision required to see fine details, such as the letters in these words or the features of a child’s face. In fact, macular degeneration is the leading cause of irreversible blindness.
The Loss of Ability to Say, “I See You”
Published in the July 18th issue of the American Journal of Clinical Nutrition, the new study concludes that what you eat may affect your vision.(1) When you eat a carbohydrate-rich food with a high-glycemic index, i.e., a snack or a meal that rapidly jacks up your blood glucose levels, you are setting yourself up for diabetes-related diseases, including retinopathy, cardiovascular disease, and now, according to this study, the loss of the ability to say, “I see you.”
Created by diabetic researchers who were investigating foods that did not instigate or accelerate diabetes, the glycemic index is a measure of how fast carbohydrates are metabolized and broken down into glucose. A food that produces glucose fast has a high-glycemic index. Foods that do this are simple carbohydrates such as white potatoes and white bread, cakes, cookies, pizza, and anything that has added sugar.
On the other hand, carbohydrates such as vegetables, brown rice, and barley have low-glycemic indices; they are broken down much more slowly. Which diet is more characteristic of how Americans eat? The answer—a real no-brainer—is the high-glycemic diet. And the real tragedy is that years of eating junk-food/fast-food diets are taking unsuspected masses of Americans to the dogs—seeing-eye dogs, that is.
Significant Higher Risk for Macular Degeneration
The study followed 4000 initially non-diabetic men and women, between the ages of 55 and 80, who were already part of a large long-term vision study. By taking photographs of the subject’s eyes at the beginning and throughout, the researchers were able to follow the development of macular degeneration over the course of the study. By grading the changing condition of 8000 plus eyes on a scale of one to five, and comparing the results with a food frequency questionnaire designed to determine the quantity of high-glycemic foods consumed, the researchers began to see a risk correspondence. After controlling for variables such as sex, age, body-mass index, and the use of alcohol, what they found was that the higher the glycemic index, the greater the chance of developing macular degeneration.
Subjects who had the worst dietary glycemic index (the top fifth), had a 40% increased risk for developing macular degeneration, compared with those with the best dietary glycemic index (the bottom fifth). The total quantity of carbohydrates consumed did not affect the risk factor. Only high-glycemic carbohydrates were associated with an elevated risk of the subjects losing their vision.
Sugar: The Good and the Bad
Glucose, as a product of carbohydrate break-down, is the body’s sugar. However though it is vociferously maligned, it is a necessary fact of life. “Sugar is fuel for the cells, but too much is destructive,” said Allen Taylor, the senior author of the paper and head of the Laboratory for Nutrition and Vision Research at Tufts University.(2) “It is known from laboratory and animal studies that carbohydrates can damage the proteins in cells and affect their function. The sugars actually modify things, modify the proteins, and it’s the accumulation of this modified stuff that is poisonous to cells.”
How this affects vision is not fully known, but the researchers believe that high-glycemic foods are responsible for oxidative stress and inflammation in the retina and the capillaries of the eyes when sugars accumulate there. Even temporary increases in blood lipid levels following consumption of simple sugars may play a role in blood vessel damage.
While other factors such as aging and smoking add to increased risk for macular degeneration, and cumulatively may be more significant than diet, what we eat is something that we can change. Although the study doesn’t prove cause and effect, risk can definitely be improved by adopting a low-glycemic diet.
- Chiu CJ, Milton RC, Gensler G, Taylor A. Association between dietary glycemic index and age-related macular degeneration in nondiabetic participants in the Age-Related Eye Disease Study. Am J Clin Nutr 2007 Jul;86(1):180-8.
- Bakalar N. Study finds dietary link to risk of eye disorder. New York Times, July 17, 2007.