Plant-based diets are often considered more healthy than a diet that includes both animal and plant protein. A new study challenges at least part of that belief. Scientists in Switzerland provided a mixed diet to laboratory animals, then switched them to plant-based foods only. After only several days, animals fed a vegan diet showed less efficient liver function along with a significant reduction in physical activity. Over time, liver issues became more severe. The findings, in the journal Molecular Metabolism, identified involvement of a specific liver enzyme—glutamate dehydrogenase—found lacking in animals fed a vegan diet. However, they noted the liver disfunction could be quickly reversed just by switching back to a diet that also included animal protein.