More and more Americans are converting to vegetarianism and veganism. The number of vegans increased by 600 percent between 2014 and 2017. More than seven million Americans are now vegetarian. Predominantly plant-based diets have benefits — but they can also cause underappreciated health problems. The reason? Those who avoid animal food products often do not get enough B-12, the much-needed vitamin found in animal products that helps build red blood cells, repair DNA, and protect the brain.