A study in mice finds that development of age–related macular degeneration (AMD) could be arrested by switching from a high–glycemic diet (starches as are found in white bread) to a low–glycemic (starches found in whole grains). For the same amount of total carbohydrate, high–glycemic diets release sugar into the blood stream more rapidly than low–glycemic diets.

Researchers at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University also believe that the study, published in the journal PNAS, points to potential biomarkers of AMD. These can be used to predict when a person is at risk for this disease, which is the leading cause of vision loss in adults over the age of 50.

Using an aged mouse model, the researchers randomized 59 mice into two groups: 19 low–glycemic fed mice and 40 high–glycemic fed mice. The diets differed only in carbohydrate source. Carbohydrates comprised 45 percent of the diet in both cases. The carbohydrate source varied in the ratio of amylose and amylopectin, the two starches used for this work. The high–glycemic starch was 100 percent amylopectin while low–glycemic starch was 70 percent amylose and 30 percent amylopectin.

After six months, the high–glycemic group of mice either remained on the high–glycemic diet or were switched to the low–glycemic diet.

The researchers observed that a high–glycemic diet resulted in the development of many AMD features, including loss of function of cells at the back of the eye called retinal pigmented epithelial atrophy (RPE) and of the cells that capture light, called photoreceptors – precursors to dry AMD – whereas a low–glycemic diet did not. Importantly, switching from a high–glycemic diet to a low–glycemic diet arrested damage to the retina.

“We were genuinely surprised that the retinas from mice whose diets were switched from high– to low–glycemic index diets midway through the study were indistinguishable from those fed low–glycemic index diet throughout the study. We hadn’t anticipated that dietary change might repair the accumulated damage in the RPE so effectively. Our experimental results suggest that switching from a high–glycemic diet to a low–glycemic one is beneficial to eye health in people that are heading towards developing AMD,” said lead author Sheldon Rowan, PhD, scientist in the Laboratory for Nutrition and Vision Research at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University.

The researchers also identified potential biomarkers of AMD features. Such biomarkers can be used to predict who will get the disease. The biomarkers included advanced glycation end products (AGEs) that are formed when sugar metabolites react with proteins. They also included oxidized fats, C3–carnitine and serotonin levels. The low–glycemic diet limited the accumulation of AGEs and the oxidation of long–chain polyunsaturated fats. AGEs can be a factor in aging and the development of many degenerative diseases, in addition to AMD.

The researchers also found that higher levels of C3–carnitine and serotonin in the blood were related to consuming the low–glycemic index diet and less AMD features.