Following a long-term diet that’s low in carbohydrates and high in fat and protein from vegetables may reduce the risk of the most common subtype of glaucoma, according to a study published in Eye-Nature. The study is important because glaucoma is the leading cause of blindness in the United States and primary open-angle glaucoma (POAG) is the most common type. POAG is the leading cause of optic nerve degeneration that is related to the pressure level inside the eye, but other factors also contribute to this condition.

Since glaucoma is a condition that may be associated with mitochondrial dysfunction, researchers wanted to find out if substituting protein and fat for carbohydrates in the diet would enhance mitochondrial activity, maintain optic nerve function, and prevent optic nerve degeneration in this blinding eye disease. They performed a large-scale meta-analysis to get this answer.

They followed 185,000 adult participants from three large studies in the United States, conducted between 1976 and 2017. Participants were female nurses and male health professionals aged 40–75. Every two to four years, they filled out food frequency questionnaires that assessed what they ate and drank. They also answered questions about their health and what diseases, if any, they might be developing. If they said they had glaucoma, the researchers asked their treating eye care providers to send medical records to determine if they had POAG.

The research team created statistical models based on the patients’ questionnaire responses, dividing them into groups based on carbohydrate intake, so they could look across the spectrum from high to low carbohydrate intake and see any possible relationship with POAG. They specifically looked at three different ways of achieving a low-carbohydrate diet: substituting animal-based fats and proteins for carbohydrates, substituting plant-based based fats and proteins for carbohydrates, and replacing carbohydrates with high fats and proteins regardless of the source. Researchers then calculated the relative risk of POAG after adjusting for multiple factors for each of the dietary patterns, including age, race, and body mass index.

The researchers found that the patients in the low-carbohydrate intake group who followed a diet of increased plant-based fat and protein were associated with a 20% lower risk of developing POAG subtype with paracentral visual field loss compared with those in the high-carbohydrate intake group. However, the researchers did not find any association between POAG and a low-carbohydrate diet without accounting for the source protein or fat, and they did not find any association between glaucoma and an animal-based low-carbohydrate diet. Their findings suggest vegetable sources may be more beneficial than animal sources for a low-carbohydrate diet with respect to reducing the risk of the specific glaucoma subtype with early paracentral visual loss.

“This was an observational study and not a clinical trial, so more work is needed as this is the first study looking at this dietary pattern in relation to POAG,” said study author Louis Pasquale, deputy chair for ophthalmology research for the Mount Sinai Health System, in a press release. “The next step is to use artificial intelligence to objectively quantify paracentral visual loss in our glaucoma cases and repeat the analysis.”

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