A diet consisting almost entirely of Pringles, french fries and white bread is to blame for one teenage boy going blind and partially deaf, according to a recently released medical study.

Since he was about 14 years old, the British boy ate mostly french fries from his local fish and chips shop, Pringles chips and occasionally a slice of processed ham with white bread. He didn’t take any supplements to balance out his diet, and didn’t really touch fruits and vegetables.

During doctor’s visits, he complained about being tired, which is a common symptom of a diet lacking in key nutrients. His medical professionals did notice that he was lacking in vitamins including B12, but chalked it up to being a fussy eater, and sent him away with some vitamin injections and instructions to eat a healthier diet.

But when he returned at age 17, it was for blindness and partial deafness. At first, doctors weren’t sure what caused it, but after more research they diagnosed him with nutritional optic neuropathy. It happens when the nerves that help make your eyes work are damaged by not getting enough nutrients. It generally develops slowly, and typically only reaches blindness if the nutritional deficiencies continue over years.

It’s a condition that’s not uncommon in the developing world, where factors like poverty, war and famine can make diets can meager and low in nutrients. But in the developing world, where more people have access to fresh, sanitary items like fruits and vegetables, it’s much rarer to see.

Good health can be deceiving. The patient’s doctors didn’t notice anything too out of ordinary with the British teen – he was within an average weight and height, and he didn’t report any symptoms at first, beyond fatigue.

Many people, medical professionals included, forget that some conditions don’t show outward signs. They expect sick, differently abled or malnourished people to display obvious symptoms, like sneezes, fainting, obviously disformed limbs or extreme weights. Some do! But even more people around the world have “invisible” diseases that a casual observer wouldn’t be able to spot.

The study should serve as a reminder both to get a second (or third! or fourth!) opinion from a medical professional if you’re sure there’s something going on that they’re not seeing, as well as to be compassionate to people around you who may be going through something without you ever knowing.

Though seemingly extreme, the teen in this medical study is a harrowing reminder of why a balanced diet is important, especially as bodies are growing and developing. It can get annoying to hear parents and teachers constantly talk about “eating the rainbow,” but they’re doing it for a reason – not getting enough vitamins can permanently change your life.

The young boy who went blind told doctors that he didn’t like the textures and feels of many foods. That’s a common problem, and if it’s one that you have, talk to your doctor about taking supplements or vitamins to help make sure you’re getting the nutrients you need. And if textures aren’t a big deal to you, try out a bunch of different vegetables, proteins, carbs and fruits to find the ones that work best for you to have a balanced diet.