Doctors diagnosed an 11-month-old baby in Spain with scurvy, a rare disease in developed countries, and believe his almond milk-only diet was to blame.

The diagnosis, described this week in the journal Pediatrics, underscores the risks of restricting infants to plant-based only diets, write the doctors at Hospital Universitari i Politècnic La Fe de Valencia.

“This case presents scurvy as a new and severe complication of improper use of almond beverage in the first year of life,” the case study authors write. They warn “plant-based beverages are not a complete food” and pediatricians and parents should be aware of this when seeking alternatives to breast milk and traditional formula.

Scurvy can be caused by a diet deficient in vitamin C. While the disease may be best known as an affliction of 18th-century pirates and explorers, people still get diagnosed with it. Children most at risk for developing scurvy are those with restrictive diets, such as those with autism.

The Spanish doctors wrote about a baby who was fed a cow milk-based formula until he was 2½ months old. He then developed skin rashes and a doctor suggested changing the diet. The baby was switched to an almond-based prepared mixture, consuming 30 or more ounces of it daily.

Once the baby turned 6 months old, his mother tried to feed him pureed fruits and vegetables, but to no avail, the authors write.

The baby seemed to be progressing and could sit without support at seven months, but one month later “he showed less interest in interacting and was more unstable when sitting,” the authors write.

By the time he was 11 months, the baby seemed to be fairly healthy but was tired and irritable. “He refused to support his legs on a solid surface” and cried if someone tried to move his legs, the authors write. Doctors found he had femur fractures and his vitamin C levels were extremely low, and diagnosed him with scurvy.

The baby was placed on vitamin C and D replacement therapy, fed a mixture of formula, fruit and meat and was cut off from the almond-based beverage.

Vitamin C, or ascorbic acid, helps produce collagen and is needed for normal growth and development. The industrial process of almond beverages causes the vitamin to lose its “biological activity,” the study authors write.

But it’s not that almond milk will cause all babies to develop scurvy. Infants who are fed plant-based beverages fare differently depending on how much they consume, and what other foods they’re fed to compensate for the nutrients they need.

The case study authors write that if fruits, formula or breast milk had supplemented this baby’s diet, he would have met his vitamin C needs.

“When plant-based beverages are the exclusive diet in the first year of life and not consumed as a supplement to formula or breastfeeding, it can result in severe nutritional problems,” the authors write.