The matter is vast, so it's difficult to give a complete answer. I start a community wiki and I hope more participants to improve my answer.
The American Dietetic Association's "Position on vegetarian diets" suggests to increase iron consumption:
Because of lower bioavailability of iron from a vegetarian diet, the
recommended iron intakes for vegetarians are 1.8 times those of
There's already a good post on this subject, that can be synthetized as:
Scientific research shows Omega 3 is not a major concern neither for
vegetarians nor vegans, since clinical trials show that omnivorous,
vegetarians and vegans showe similar blood levels of Omega-3s. This could
be due to increased capability to convert ALA into EPA and DHA. If
intervention studies were to confirm these findings, it could have
implications for omega-3 requirements.
Whole products and phytic acid
Phytic acid, present in whole meal products, can inhibit absorption of several minerals, such as zinc, iron and calcium, and possibly also magnesium and copper. However sourdough fermentation can prevent phytic acid to cause this decreased absorption. (Lopez 2002)