In the news: Switching to a Low-Glycemic Diet May Help Arrest AMD Development

Low Glycemic Diet May Help Deter AMD

Several analyses of participants in the AREDS trial and the Nurses Health Study have reported an association between a high glycemic index diet (dGI) and early signs of AMD, or that consumption of a low dGI is associated with decreased AMD risk (1). Among non-diabetic AREDS participants, a positive association was observed between high dGI and large drusen in early AMD, and a 49% increased risk of advanced AMD (geographic atrophy plus neo-vascularization) was associated with a dGI higher than the median for men and for women (2). These findings suggest that dGI may influence the risk of both early and late AMD.

The glycemic index (GI) is a scale that ranks carbohydrate-rich foods by how much they raise blood glucose levels compared to a standard food, usually glucose or white bread. High GI foods include sweets, white rice and bread, processed cereals and French fries, while lower GI foods are generally fiber-rich such as beans, whole grain bread, brown rice and oatmeal.

Switching to a Low Glycemic Diet Arrests AMD

To learn more about transitioning from a high to a low dGI, researchers from Tufts University’s Human Nutrition Research Center performed a study (3) using an aged mouse model. Fifty-nine mice were randomized to either a low dGI or high dGI. The only difference between the diets was the carbohydrate source. After 6 months, the mice fed the high dGI either remained on that diet or were switched to the low dGI.

High dGI promoted the onset of several AMD features: retinal pigmented epithelial atrophy, photoreceptor dysfunction and lipofuscin accumulation. These AMD precursors were not seen in the mice fed a low dGI.

Critically, mice that were moved from the high to the low dGI midway through the study had retinas that were indistinguishable from those of the mice fed a low dGI for the entirety of the study. This dietary alteration appeared to effectively repair the damage that had accumulated while on the high dGI.

Potential AMD Biomarkers

The researchers also identified potential biomarkers of AMD features. Low dGI diets limited the accumulation of advanced glycation end products (AGEs), long-chain polyunsaturated lipids and their peroxidation end-products, and increased C3-carnitine in retina, plasma, or urine.

AGEs are known to be a factor in aging and in the development of many degenerative diseases, including AMD. Lipid peroxidation results in the degradation of cellular membrane lipids. C3-carnitine (propionylcarnitine) plays a role in cellular fatty acid metabolism, and it is found in many low-glycemic foods, such as whole wheat and legumes.

Higher levels of serum serotonin were also related to consuming the low dGI and less manifestation of AMD features. Serotonin is produced in the intestine in response to signals from gut microbes.

The researchers found that gut microbiota were responsive to diet, identifying microbiota in the Clostridiales order as being associated with AMD features and the high dGI, while protection against AMD features was associated with the Bacteroidales order and the low dGI. These observations led the authors to postulate that there may be a gut-retina axis to protect against diet- and age-induced AMD.

These findings add to a growing body of research on the relation between the quality of the dietary carbo-hydrates we consume and the development of AMD. While long-term prospective trials are needed to confirm the salutary effects suggested by this and previous investigations, a high dGI has already been implicated in the development of diabetes, CVD and some cancers.

References

1. Chiu CJ, et al. Dietary glycemic index and carbohydrate in relation to early age-related macular degeneration. Am J Clin Nutr 83:880-86, 2006.
2. Chiu CJ, et al. Association between dietary glycemic index and ARMD in non-diabetic participants in the Age-Related Eye Disease Study. Am J Clin Nutr 86:180-8, 2007.
3. Rowan S, et al. Involvement of a gut-retina axis in protection against dietary glycemia-induced age-related macular degeneration. Proc Natl Acad Sci. 114:E4472-E4481, 2017.