For all the crap that vegans get, their diet can be quite good for you and good for the planet as it keeps you from eating foods heavy in fats and makes you indulge in more produce; plus, it reduces reliance on livestock for food, lowering the impact on the environment. But vegans can be a little rigid (and often insufferable) with their borderline-evangelical insistence on toeing the vegan line, which can lead to nutritional deficiencies and unhealthy practices if they aren’t up on proper guidelines.

Case in point is a recent presentation from the annual European Society of Paediatric, Gastroenterology, Hepatology, and Nutrition (ESPGHAN) meeting, which found that young kids who are on a vegan diet and not given proper medical and dietary advice are at a higher risk of having low levels of nutrients like vitamin B12, calcium, zinc, and protein. They also noted that, in general, children on a vegan diet are leaner and smaller than kids who eat meat or are even vegetarians.

Being deficient in vitamin B12—which is only dependably found in animal sources—presents a major danger because it helps create DNA and helps maintain the nervous system, and, if you don’t have enough, blood and neurological disorders can develop, causing irreparable damage to kids’ health. Skipping out on milk is also big area of concern, as the supplements vegan parents turn to like rice milk, soy milk, and almond milk don’t have the proper nutrition and calcium levels that infants need to develop the normal bone density that sets them up for strong bones for life.

"It is difficult to ensure a healthy and balanced vegan diet in young infants, and parents should understand the serious consequences of failing to follow advice regarding supplementation of the diet,” said Mary Fewtrell, M.D., chairman of ESPGHAN's nutrition committee. “The risks of getting it wrong can include irreversible cognitive damage and, in the extreme, death. Our advice is that if parents pursue a vegan diet for their child, they must seek and strictly follow medical and dietary advice to make sure their infant receives adequate nutrition.”