Children who are vegans and vegetarians may not be getting all the nutrients they need from their diets, a group of international researchers said Friday.

Plant-based diets have been shown to reduce the risk of heart disease and support the immune system. But a new peer-reviewed study of 48,000 children and adolescents - the largest of its kind - found that vegetarian children consumed lower amounts of calories, protein, fat, the essential mineral zinc and nerve-supporting vitamin B12.

Similar patterns were seen in kids on a vegan diet, who were especially low on bone-strengthening calcium.

“Notably, vitamin B12 didn’t reach adequate levels without supplementation or fortified foods, and calcium, iodine and zinc intakes were often at the lower end of recommended ranges, making them important nutrients to consider for children on plant-based diets,” Dr. Jeannette Beasley, an associate professor at New York University and one of the study’s authors, explained in a statement.

The study reviewed 59 studies across 18 countries, comparing the nutritional health outcomes of 7,280 vegetarians, 1,289 vegans and 40,059 omnivores, who eat both plants and animals.

Siblings watch a chef prepare a healthy snack of fruits and vegetables in July 2002 in Miami Beach, Florida. Children who eat vegan and vegetarian diets are low on some key nutrients, according to a large new study (Getty Images)

A boost to heart health

While the study’s analysis revealed deficiencies in plant-based diets, it also highlighted the benefits.

Vegetarian kids got more gut-boosting fiber, iron, folate and vitamin C than omnivores, and both vegan and vegetarian children had better heart health.

These children had lower levels of bad cholesterol, a build up of a waxy fat-like substance that can block blood flow to the heart and be a risk factor for life-threatening heart attacks and strokes later in life.

“The more you eat animal products, which displace whole food, plant-based foods, the worse off your cardiovascular health,” Dr. Dana Hunnes, a senior dietitian at Ronald Reagan UCLA Medical Center who was not involved in the study, said last year.

Vegan and vegetarian kids were shorter and had a lower body mass index than omnivores, too, reducing the risk for obesity and diabetes - conditions that can also hurt heart health.

Kids who eat plant-based foods have better heart health than kids who eat meat (Getty Images/iStock)

Small snacks, big difference

While the findings show that kids on plant-based diets might not get as much B12 or zinc, they can get enough by planning out their diet to include more of certain plant-based foods.

While non-vegetarian foods tend to be higher in zinc, lentils, pumpkin seeds and cashews are some of the best sources on a plant-based diet, according to Harvard Medical School. Cashews have the most, providing nearly eight grams of zinc per cup.

Those foods can be toasted and mixed with salt and olive oil for a fun snack, or mixed into a soup or smoothie. Plant-based kids can get more vitamin B12 by eating more seaweed or shiitake mushrooms.

One hundred grams of shiitake mushrooms contains an average of 5.6 micrograms of vitamin B12.

Children should get between three and 11 milligrams of zinc, depending on their age, according to Stanford Medicine, and between 0.9 and 2.4 micrograms of vitamin B12.

“Our findings suggest that a balanced approach is essential, with families paying close attention to certain nutrients - particularly vitamin B12, calcium, iodine, iron and zinc - to ensure their children get everything they need to thrive,” Dr. Wolfgang Marx, a co-author and senior research fellow at Australia’s Deakin University, said.