By Jamie Ducharme
September 3, 2019

A new case study highlights a serious, though rare, side effect of a poor diet: blindness.

In the Annals of Internal Medicine, a group of researchers from the University of Bristol in the U.K. report the unusual case of a teenage boy whose diet was so poor, it led to serious optic nerve damage and vision loss.

The boy first reported fatigue to his doctors when he was 14. He was deficient in vitamin B12 but had few other health issues, so he received only vitamin B12 injections and dietary counseling.

The next year, he began to experience hearing and vision disturbances, but doctors were unable to find a clear cause.

After two years of worsening eyesight and eventual blindness, the boy was referred to a neuro-ophthalmologist. At that time, doctors found signs of continuing vitamin B12 deficiency, as well as other nutritional deficiencies—and, upon interviewing the boy about his diet, found that “since elementary school, he would not eat certain textures of food.” The patient was mostly subsisting on french fries, Pringles, white bread, ham and sausage, according to the case report.

Diet-related vision loss is fairly common among populations where poverty and food insecurity are widespread. When it occurs among people in developed nations, it’s typically related to an inability to absorb certain nutrients, or combined with alcohol or tobacco use. A purely diet-related case of vision loss is rare—especially in a young, otherwise healthy patient living in a rich country. The authors theorize that the boy’s extremely limited diet led to deficiencies in B vitamins and copper, which became severe enough to contribute to nerve damage and vision loss.

“The visual loss is reversible in the early stages. The problem with this case is that his poor diet continued over several years,” says case study co-author Dr. Denize Atan, a neuro-ophthalmologist who treated the patient at Bristol Eye Hospital. “To give some perspective, he had a poor diet [starting] from age 10 to 11 but only started to develop symptoms age 14. It takes this long to deplete your body’s stores of these vitamins.”

In this case, the boy’s vision did not return, even with nutritional supplements.

The case report highlights not only the necessity of a balanced diet, but also a little-discussed form of disordered eating, one that isn’t necessarily related to weight or body image. “‘Fussy eating’ that is restricted to junk foods and causes multiple nutritional deficiencies is an eating disorder,” the authors write. People who are not interested in food or strongly dislike certain textures may fall into this category, according to the report.

When patients report very restrictive diets, doctors should be aware of the full range of potential consequences, Atan says. “A good rule of thumb is to assume someone with a poor diet and at least one deficiency is likely to have others too and to treat them all—not just the one you have detected in a single test,” she says.

Write to Jamie Ducharme at jamie.ducharme@time.com.

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