We all know a vegan lifetsyle can be a little tricky when it comes to getting vitamin B12; so tricky in fact, that we need to get our daily boost from fortified foods or supplements. Correspondingly, the biggest nutritive no-no a vegan could do would be to give it some due attention. Recently, a survey study in the Journal of Agricultural and Food Chemistry gave many vegans a failing grade in maintaining healthy levels of omega-3 fatty acids and vitamin B12.
Before you make a run to the local butcher, several other health professionals piped in with their take on the findings. Vesanto Melina, a noted vegan writer and dietitian, disagrees with the findings (via the Globe and Mail). David Jenkins, a professor of nutritional sciences at the University of Toronto, also disagreed with the researcher's conclusion.
Rest assured, hospitals aren't stuffed to the gills with vegans dying of, well, their veganism. However, B12 is dodgy stuff; as we know, it's not available for human absorption from plant-based foods. It plays an essential role in maintaining brain function and keeping your nervous sytem running on the up-and-up. A vitamin B12 deficiency can be ghasty for little ones especially, and can lead to poor gastrointestinal and neurological function. Long story short, if you take one health risk seriously in terms of your veganism, let it be maintaining a steady load of vitamin B12.
Vegan sources of B12? Your best bet is fortified foods. One cup of most (but not all) non-dairy millks will supply roughly 50% of the suggested dosage required daily. Other sources are many breakfast cereals, nutritional yeast -- even some ready-made "vegetarian" entree items like veggie burgers carry it. Again, important to check food labels, here. Some vegan propenents maintain that things like seaweed and barley grass. Again, that stuff contains B12, sure, but the problem is our bodies don't absorb it particularly well.
At the end of the day, many dietitians suggest taking a daily or weekly supplement. Generally speaking, adults require about 2-3 ug per day, so check the label of your multivitamin, if you take one. This should also be considered if you have just taken a run of antibiotics as well -- the most prescribed systemic antibiotics are going to leave your body gasping for a B12 fix.
As for omega-3's, I'll do you one better and urge you to take a look at the Toronto Vegetarian Association's document of veggie nutrition.
(I've said it once and I will do so again, Ms. Melina's book, Becoming Vegan, co-authored with fellow dietitian Brenda Davis, should be your go-to resource for any diet info you might require.)