He was diagnosed with nutritional optic neuropathy.

By Renee Cherry
September 03, 2019
Sally Anscombe/Getty Images

At this point, you're probably well aware that ultra-processed foods shouldn't make up the bulk of your diet. But a recent case study highlights a potentially extreme impact of eating exclusive junk food: One teen in the UK went blind, and experts think his limited diet is to blame. (Related: Should You Really Hate On Processed Foods?)

The study, published in Annals of Internal Medicine, centered around the case of a boy who was an extremely picky eater, who apparently survived on chips, fries, white bread, and processed pork alone...for years. He checked in with a doctor at age 14 about fatigue, and again a year later with hearing loss and vision issues.

His doctor found that he had low vitamin B12 levels, and treated him with B12 injections and provided dietary advice, according to the study's press release. But the teen's vision continued to decline, and by the time he was 17, he'd gone blind. At that point, tests revealed that in addition to a vitamin B12 deficiency, he had low copper, selenium, and vitamin D levels, a high zinc level, and reduced bone density. His vision was permanently impaired. (Related: Why B Vitamins Are the Secret to More Energy)

It gets scarier: The teen had a BMI considered to be within the normal range, and he hadn't shown any visible signs of malnourishment. Had he shown more signs, medical professionals might've picked up on the link between his vision problems and diet sooner.

"This case highlights the impact of diet on visual and physical health, and the fact that calorie intake and BMI are not reliable indicators of nutritional status," lead study author Denize Atan, Ph.D., consultant senior lecturer in ophthalmology at Bristol Medical School and clinical lead for neuro-ophthalmology at Bristol Eye Hospital, stated in the press release. (Related: A Woman Temporarily Went Blind After a Salon Used Nail Glue to Apply Her Lash Extensions)

The researchers who studied the case concluded that the teen's limited diet led to nutritional optic neuropathy, a condition in which a lack of nutrients affects the function of your optic nerve (the nerve that sends signals from the retina to the brain). Nutritional optic neuropathy resulting solely from dietary choices (rather than bowel issues, meds that affect nutrient absorption, etc.) usually happens in countries where malnourishment is prevalent, but that might be changing because of the emergence of processed foods, the researchers warned.

That said, even if you eat a lot of junk food, you probably won't experience nutritional optic neuropathy, as long as you're eating other foods, too. "An individual with no bowel concerns or drug consumption would need to be extremely underfed and malnourished to experience these same optic neuropathy effects," says Brittany Michels, R.D., a consulting dietitian with The Vitamin Shoppe. "Junk food alone isn't what impacts nutritional deficiencies. It's the overall diet. The teen in this case study sounds like he was eating only junk food, without other meals to supplement needed nutrients."

Even if you're not eating the extremely limited type of diet that can lead to nutritional optic neuropathy, it doesn't hurt to be aware of your potential nutrient gaps. Fatigue, sluggishness, irritability, emotional changes, and frequent sickness and sleep disturbances are all possible signs of malnourishment, explains Michels. "It's important to be in tune with your body and to recognize symptoms and changes," she says. "If you're on a restrictive diet and unsure if you're meeting nutritional needs, consult a dietitian."


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