Diet, Gut Bacteria, and AMD – New Research Shows the Connection
This research was supported by BrightFocus
Some of the newest BrightFocus-funded research is exploring whether our diets affect our microbiome – the microorganisms that live within our body and guts – and whether that in turn has an impact on the risk and severity of macular degeneration.
It is normal for humans to host teeming colonies of microorganisms that help out with things like digestion and producing needed compounds from our food. In fact, it’s estimated that non-human cells living in our body outnumber human cells by about three-to-one, and science has become keenly focused on how the make-up of our microbiome affects our health.
Sheldon Rowan, PhD, a 2017-19 MDR grantee at Tufts University in Boston, is studying how diet affects the composition and function of the microbiome. One of his co-principal investigators is Allen Taylor, PhD, senior scientist and director of the Nutrition and Vision Research Laboratory at the USDA Human Nutrition Research Center on Aging at Tufts, where Rowan himself is based. Together they are leaders in studying the aging eye and how nutrition affects diseases such as age-related macular degeneration (AMD).
“You might think that there is no connection between your gut and the eye,” Dr. Taylor said, observing how far apart they are in the body, and that “even biologically they seem to be unrelated.”
Nonetheless, “there is certainly a functional relationship between the diet, the microbiome with the gut bacteria, and your eyes,” he confirmed, explaining that the gut makes compounds that are absorbed into the bloodstream and “may affect the vitality and the function of your eyes.”
In humans, Taylor and Rowan have compared the effects of a high-glycemic, high-fat diet with what they’re calling a “prudent” diet rich in fruits, vegetables, and fish. “High glycemic” diets have a high concentration of refined sugars and starches.
“What we found is that people who consumed diets that deliver sugar rapidly to the bloodstream, which we call a high glycemic index diet, those diets are clearly associated with a greater risk for macular degeneration of all stages—be it advanced or early macular degeneration—when compared to people who consume lower glycemic index diets,” Dr. Taylor said.
They also found that relatively small changes can make a difference between a high and low glycemic diet. “We are not asking people to not eat bread, or not eat pasta, or not eat potatoes or corn, but rather to replace a little bit of that with something that is more whole grain or something that liberates the sugar more slowly,” he said.
Now the team is moving ahead to test the notion that the so-called “prudent diet” is in fact associated with a healthier gut microbiome for the eyes. “In order to do the proper experiments, what one should do is not just change the diet but change the microbiome per se, and see if it affects your eyes,” Dr. Taylor said. “We are just beginning that work now.”
Early evidence has emerged in mice. “When we put mice on low-glycemic-index diets, they had a different microbiome and different gut bacteria from the mice on high-glycemic-index diets. Certain products of that microbiome were related to retinal health,” he said.
Furthermore, when mice fed a high-glycemic-index diet were switched back to a low-glycemic-index diet, their microbiome also switched back to one that resembled the low-glycemic-index group, and “their retinal disease was arrested,” Dr. Taylor said. “So, we think that this forms an ecology in which you have diet, you have microbiome, you have the body, and all of these are working together to affect your vision.”
Could this approach help delay or reverse AMD?
“If that same information plays out in humans, then I think we can delay the onset of AMD,” Dr. Taylor said.
“We were very excited to find that these relationships all helped with early macular degeneration. To the extent that you can arrest or delay the progress of the early disease, you preserve vision for that many more years!”