July 22, 2007
High Glycemic Index Diet Linked To Blindness

One cause of blindness in old age happens more often in people who eat high glycemic index diets.

BOSTON -- Age-related macular degeneration (AMD) and its associated vision loss may be connected to the quality of carbohydrates an individual consumes. In a study published in the July issue of the American Journal of Clinical Nutrition, Allen Taylor, PhD, director of the Laboratory for Nutrition and Vision Research at the Jean Mayer USDA Human Nutrition Research Center on Aging (USDA HNRCA) at Tufts University, and colleagues confirmed earlier findings linking dietary glycemic index with the risk of developing AMD.

"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 carbohydrates in lower glycemic index foods break down more slowly into simple sugars in the digestive tract. Therefore the sugar enters the bloodstream more slowly and blood sugar levels do not spike as high. It is those high blood sugar level spikes that cause damage to eyes and to other parts of the body. For this reason diabetics age more rapidly and suffer from blindness, loss of circulation in the extremities, and other problems. We can probably expect a lower glycemic index diet to reduce the incidence of some of the diseases that plague diabetics.

It is worth noting that people who eat lower glycemic index diets are typically eating more vegetables and whole grains that contain assorted beneficial compounds. So I don't think we can be certain whether the benefit reported here is totally due to the lower glycemic. However, it doesn't matter in one sense. If you eat the vegetables that lower dietary glycemic index you'll get the benefits regardless of the mechanisms of action.

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.

Rices come in a large range of glycemic indexes. The sticky rice found in Chinese restaurants has one of the high glycemic indexes. Basmati rice is much lower and Uncle Ben's Converted Rice lower still. But grains including rice are generally higher in glycemic than beans and vegetables. If you want to eat a low glycemic index diet best to cut way back on grains and eat more beans, vegetables, and fruits.

Eating a lower glycemic index diet could probably cut your AMD risk by 20% and maybe more.

"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, who is also a professor at the Friedman School of Nutrition Science and Policy at Tufts and the Tufts University School of Medicine. "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.

The mechanism by which high glycemic index foods boost your risk of blindness also probably does damage in other parts of your body. So lowering your diet's average glycemic index will deliver other benefits. Plus, if you lower your glycemic index by eating more vegetables you'll benefit from vitamins and assorted other beneficial nutrients found in vegetables.

Check out David Mendosa's chart of glycemic index and glycemic load for hundreds of foods.

Update: Another way to reduce the risk of AMD: genetically engineer yourself to have genes that lower your risk of AMD.

They found that a variant in the complement C3 gene influenced the risk of developing AMD. For the 30% of the population who carry one copy of the so-called ‘fast’ variant the risk of AMD was increased by 70%, and for the 4% of people with two copies of the ‘fast’ variant the risk of AMD was more than doubled.

AMD can take two forms called ‘wet’ (also called choroidal neovascularisation or CNV) and ‘dry’ (also called geographic atrophy or GA). The ‘fast’ variant in the C3 gene increases the risk of both forms of the disease.

The complement C3 gene has a central role in the immune system. The results of this research provide strong evidence that inflammation is an important part of the disease process in AMD.

I think we are going to find that the diseases in our ancestral past selected for humans who have over-enthusiastic immune systems that cause damaging inflammation.

Share |      Randall Parker, 2007 July 22 08:56 PM  Aging Diet Eye Studies

Nancy Lebovitz said at July 23, 2007 12:33 AM:

It is worth noting that people who eat higher glycemic index diets are typically eating more vegetables and whole grains that contain assorted beneficial compounds

I think you meant "people who eat lower glycemic index diets".

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