Switch to a Low-glycemic Diet : Stop Age-related Eye Disease

Highlights

• Age-related Macular Degeneration (AMD) affects the macula, causes gradual loss of central vision and does not have a possible cure.
• Switching from a high-glycemic diet to a low-glycemic one is beneficial to eye health in people that are heading towards developing AMD.
• Changes in metabolism associated with the different glycemia diets are related to AMD features.

Food habits and change in dietary patterns help in the treatment of most diseases. As far as diabetes is concerned, dietary change is crucial as elevated levels of blood glucose levels can damage other organs such as the eye, heart, kidneys and the foot.

How Serious Is Macular Degeneration?

Age-related Macular Degeneration (AMD) is a disease associated with aging and is most commonly diagnosed in diabetics. It is a degenerative condition that affects the macula and causes gradual loss of central vision. Macula is the area on the retina responsible for central vision. It has the maximum concentration of color sensitive cone cells which help clear high contrast vision with color distinction. The disease is now a leading cause of blindness in the developed world in persons aged over 65yrs. 

AMD results in blurred vision at the early stages and can make life challenging in advanced stages. In 2010, 2.5 percent of white adults in the US aged 50 and older had AMD. Globally, the number of people with AMD will double by 2050, from 2.07 million to 5.44 million, according to the National Eye Institute.

The disease causes vision loss and there is no cure. So, preventing AMD in at risk individuals is a key step to reducing the disease burden.

How Does Glycemic Index (GI) Influence AMD?

Researchers at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University find that a low glycemic index diet has the potential to reduce certain biomarkers that indicate AMD.

Glycemic index (GI)  is a scale which helps rank carbohydrate- rich foods, depending on how they affect blood glucose levels, by comparing them to glucose.

GI measures how much your blood sugar level increases in a span of 2 - 3 hours, post consumption of food. 

Development of age-related macular degeneration (AMD) could be arrested in mice by switching from a high-glycemic diet (starches found in white bread) to a low-glycemic (starches found in whole grains).

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GI is possibly one of the scientific ways of looking at carbohydrate-rich food and finding out which item, when consumed, is likely to increase the level of glucose in the blood. 

Carbohydrates with high GI causes a rapid increase of blood sugar, whereas diet based on low GI are low in sugar but high in fiber. They cause a slow rise of blood sugar and are, therefore, ideally suited for diabetic patients.

Low vs High Glycemic Index (GI) Diet

The researchers randomized 59 mice into the low and high glycemic index diets. Carbohydrates comprised 45 percent of the diet in both cases. The carbohydrate source used in the high glycemic index diet was 100 percent amylopectin while 70 percent amylose and 30 percent amylopectin was used in the low-glycemic starch group.

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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 the cells that capture light, called photoreceptors - precursors to dry AMD. Switching from a high-glycemic diet to a low-glycemic diet arrested damage to the retina.

What is a Low Glycemic Index Diet?

A low-glycemic index diet includes foods such as fish, eggs, fruits, vegetables, whole grains that can help in preventing blindness and other eye related conditions. "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, Ph.D., scientist in the Laboratory for Nutrition and Vision Research at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University.

Identifying Potential Biomarkers of AMD

The researchers also identified advanced glycation end products (AGEs), oxidized fats, C3-carnitine and serotonin levels as potential biomarkers of AMD features.

Senior author Allen Taylor said, "Currently, there are no early biomarkers to anticipate the disease. Our findings show an interaction between dietary carbohydrates, the gut microbiome, specific biochemical molecules, and AMD features. This work should lead to new approaches to understand, diagnose and treat early AMD - perhaps before it affects vision.”

• AGEs are formed when sugar metabolites react with proteins. Apart from AMD, AGEs can be a factor in aging and the development of many degenerative diseases. The low-glycemic diet limited the accumulation of AGEs and the oxidation of long-chain polyunsaturated fats. Fat oxidation results in the degradation of fats in cell membranes, which can lead to cell damage.
• C3-carnitine, also known as propionylcarnitine is found in many low-glycemic foods, such as whole wheat and legumes. It plays a role in fatty acid metabolism in cells. A low glycemic index diet elevates the levels of C3-carnitine and serotonin in the blood and less AMD features.
• Higher serotonin levels are associated with reduced frequency of AMD features. Serotonin is made in the intestine, in response to signals that are produced by microbes in the gut. The researchers showed that the composition of gut microbes, collectively called the gut microbiome, changes in response to the diet.

The researchers identified several other metabolites that were associated with protection from AMD and with the composition of the gut microbiome, which together led the authors to speculate on a potential gut-retina axis that may communicate diet to eye health.

Glycemic indices influence the changes in metabolism and they reflect in AGEs accumulation, production, oxidation of fats, C3-carnitine and serotonin levels. These findings add to a growing body of research on the relation between dietary carbohydrate control and the development of AMD.

"Already anticipated by our human epidemiologic studies, the findings imply that we can develop dietary interventions aimed at preventing the progression of AMD, a disease which impacts millions and costs billions worldwide," said Taylor.
Reference:

1. Rowan, S., Jiang, S., Korem, T., Szymanski, J., Chang, M., Szelog, J., Cassalman, C., Dasuri, K., McGuire, C., Nagai, R., Du, X., Brownlee, M., Rabbani, N., Thornalley, P.J., Baleja, J.D., Deik, A.A., Pierce, K., Scott, J.M., Clish, C.B., Smith, D., Weinberger, A., Avnit-Sagi, T., Lotan-Pompan, M., Segal, E., Taylor, A.. Involvement of a gut-eye axis in protection against dietary glycemia induced early age-related macular degeneration. Proceedings of the National Academy of Sciences, (2017). DOI: http://www.pnas.org/cgi/doi/10.1073/pnas.1702302114

Source-Medindia