Both can produce health if followed wisely.
Both can produce illness if not followed wisely.
Vegan, even vegetarian eating, require a lot MORE knowledge about nutrition.
Any diet program that limits what foods you are eating will require more nutritional knowledge in order to eat wisely.
There are two advantages to eating vegetarian or vegan:
(1) It is a more efficient use of Earth's resources. It takes far less land to grow food to feed a vegetarian/vegan for a year than it does to graze enough cattle to keep you in meat for a year.
But since the population of Earth is still mostly eating meat, your diet change won't impact the Earth.
it is primarily an ideological stance, once that helps you like yourself better.
(2) Not eating meat or animal products out of compassion for animals. Again, this is an ideological stance, and not one that is going to reduce the suffering that meat production causes for animals.
(3) Plant protein is less expensive, financially, than animal protein. You do not need to buy supplements if you eat the right proportions of foods.
No matter how wisely we eat, we are going to end up dying. Usually from something that we have a genetic predisposition for.
Not to downplay the carcinogenic effect of technology on both our environment and our foods ...
but I am not necessarily advocating organic food either.
Understand that soil can be depleted of minerals, even organic soil .. and that veggies grown on depleted soil will lack minerals.
No, vegan diets do not result in nutritional deficiencies if you know what you are doing.
I eat meat, but I've known people who do eat a lot of fast food, and the only veggies they get are the pickles and lettuce in their Big Mac and the mushrooms on their pizza. Talk about nutritional deficiencies!
One big draw-back to eating vegan or vegetarian is that you usually spend more time IN the kitchen preparing tasty meals. So unless you enjoy cooking, these are not happy diet plans to undertake. Rice, legumes, quinoa .. they all take time to prepare and are pretty bland unless you add herbs and spices, onions, garlic, etc.