In the July issue of the American Journal of Clinical Nutrition, Dr. Allen Taylor and colleagues of the Laboratory for Nutrition and Vision Research at Tufts University confirmed earlier findings linking dietary glycemic index with the risk of developing AMD. Here's how Taylor describes this work, and the lessons learned from his research:
“Men and women who consumed diets with a higher glycemic index than average for their gender and age-group were at greater risk of developing advanced AMD,” corresponding author Taylor says. “The severity of AMD increased with increasing dietary glycemic index.”The risk for AMD may be diminished by improving dietary carbohydrate quality, as defined by dietary glycemic index. This may be achieved by relatively simple dietary alterations, such as replacing white bread with whole grain bread.
Glycemic index is a scale applied to foods based on how quickly the carbohydrates in foods are converted to blood sugar, or glucose. Foods like white rice, pasta and bread are examples of foods with a high-glycemic-index, meaning that these foods are associated with a faster rise and subsequent drop in blood sugar. Whole wheat versions of rice, pasta and bread are examples of foods that have a low-glycemic-index. These foods are often considered higher quality carbohydrates because they are associated with a slower and less dramatic rise and fall of blood sugar.
In this study, Taylor and colleagues analyzed data from 4,099 men and women participating in the nationwide Age-Related Eye Disease Study (AREDS). Detailed dietary histories were obtained at the start of the study when participants were 55 to 80 years of age and had varying degrees of AMD.
“Although carbohydrate quality was not the main focus in the AREDS, we were fortunate that the investigators had collected the dietary carbohydrate information we needed to do our analyses,” says Taylor. “Our findings suggest that 20 percent of the cases of advanced AMD might have been prevented if those individuals had consumed a diet with a glycemic index below the average for their age and gender,” notes Taylor.
AMD typically occurs after middle age, although the events which cause it may begin earlier. A leading cause of irreversible blindness, AMD results from the gradual breakdown of light-sensitive cells in the central region of the eye’s retina, called the macula. Although there is no effective therapy for AMD, dietary intervention may delay its progress. Identifying modifiable risk factors for AMD is becoming increasingly important as the population ages. As Taylor and colleagues point out, the number of people in the US with visually impairing AMD is expected to double and reach three million by 2020.
Taylor speculates that carbohydrates that comprise a high-glycemic-index diet may provide eye tissue with too much glucose too quickly, and overwhelm the ability of the eye cells to use the carbohydrate properly. “It is possible that the type of damage produced by poor quality carbohydrates on eye tissue is similar in both diabetic eye disease and AMD.”