(As a side note, your local hospital's cardiac, stroke, and cancer units are likely to have 100 percent omnivores filling those beds, but I digress.)
You can't simply knock out meat and animal products and think you're going to be healthy. One has to be educated on what to replace those animals products with. (And by the way supplementing with B12 is ESSENTIAL if you are vegan.)
You can get enough protein with beans, nuts, seeds, some nut milks, tofu, etc. but here's the deal. Eating vegan or vegetarian and doing it right requires planning and learning how to cook. Eating meat is wonderful and tasty and easy. Vegan/vegetarian cooking is more challenging.
There's tons of books and websites devoted to both so if that's the route you choose educate yourself. It's not as simple as switching to salads and fruit.
Vegetarianism is a food cult. Humans are carnivores. Period.