It's not all good news: You may need to supplement
A vegetarian diet may require the use of certain supplements, or at least carefully crafted meals, which can ensure the requisite amounts of nutrients that might be lost in transition. One common problem people have when flushing out the flesh foods is a zinc deficiency, since that vitamin is most often found in red meat and shellfish. Plus, vegetarian foods are high in phytic acid which interferes with zinc absorption. The effects of that deficiency may include a weakened immune system, loss of memory, eyesight and tastebuds, an onset of diarrhea, allergic reactions, hair loss, and rashes. The good news is there's a relatively simple fix for that: foods like mushrooms, spinach, cashews, chickpeas and cocoa powder are all great sources of zinc, so bring 'em into the routine, and make up the difference.
Other essential vitamins that may become depleted in the process of becoming a meat-free eater include B12, calcium, iron. For those that are careful with their menus, however, this can be addressed without the use of vitamin supplements. Vitamin B12 is found in yeast and certain cereals, while calcium can be derived from foods like almonds, bread, milk, and sesame seeds. Nuts, dried fruit, beans, and broccoli are all high in iron and would be assets to a vegetarian's diet.
Vegetarians should also make sure that they're incorporating enough protein into their daily meals, which can be accomplished by eating eggs, cheeses, lentils, black beans, and tofu.