I agree with you there silva about fish. Sardines for example contain high amounts of b12, calcium, protein, dha, even D, and a small amount of K2 all in one little serving, all nutrients that are harder or impossible to get from plant food. Though sardines are also high in fat and cholesterol. And there is some risk of mercury contamination and other environmental issues associated with fishing. Never mind the cruel way that sardines are caught in the wild or kept in captivity and bred.
I became vegan purely for ethical reasons. I went from omni to vegan six years ago and have stayed vegan for six years now. However, I do worry sometimes about meeting some nutritional needs. Though I am relatively healthy, and my hemoglobin, iron, B12, glucose, triglycerides, LDL/HDL etc have all tested very healthy over the years as a vegan, I have a long history of several health problems that are challenged by eating a vegan diet. I have a history of anorexia nervosa, and a very long history of hypothyroidism spanning back to 1988. I have to be careful with soy intake, and intake of cruciferous vegetables. I don't avoid them, but I am careful and consume them in moderation. I will not allow myself to restrict my diet too much because that always leads to bad things for me. I need to be more flexible within the vegan realm. I also have a long history of osteoporosis spanning back to when I was diagnosed at 34 years of age in 2006. I lost my ovaries and uterus the year before so I had a baseline DXA scan and was shocked at how bad my results were. Over the years my bone density has declined rapidly (despite intense weight bearing exercise, hormone replacement therapy, supplements), and I am now on medication for it. I was doing well until last November/December when I injured my back and it will not heal. I have another appointment Friday for yet another opinion. I am trying to be more diligent about getting plant food sources of calcium, magnesium, zinc, potassium etc and not rely too much on supplements alone because they are less well absorbed. I'm not going to lie that I have daydreamed and thought about stepping down to vegetarian but I can not get past the ethical issues at all with consuming dairy and where it comes from and what cows are put through. I just can't. I had an intolerance to most dairy for years before I went vegan anyway, with the exception of Greek yogurt, which I read somewhere some time ago has a lowered amount of lactose due to the extra processing step?
However, I think a vegan diet CAN be very healthful and beneficial in general, and especially for certain subgroups of people suffering from certain diseases like cancer, heart disease, diabetes II. We have the benefit of no cholesterol in the foods we consume, and most of us have far less trouble getting in our required amount of fruits and vegetables each day.
I personally eat about 80% whole foods but allow plenty of room for some processed foods....vegan mayo, plant milks, occasional veggie burgers or plant "meat", vegan yogurts...It is part of fighting my eating disorder but also I happen to enjoy some processed foods and find nothing wrong with including them occasionally.
I find that the ethical and environmental benefits of being vegan far outweigh that of vegetarian. The animal farming industry is brutal in so many ways, and an inefficient way of obtaining nutrients considering the energy and space farm animals require, and the care.