Bruce wrote in
:

Being a vegan isn't easy. I married someone strictly vegetarian who
is keen to go vegan, so I know. But many people seem to achieve a
dairy-free diet quite successfully.

The key difficulties are to get enough B12 and calcium. Note that
deficiencies in those take *decades* to appear, so it is entirely
possible that someone that become a vegan diet can easily appear
to be getting adequate nutrition.

Often vegans correctly state that there are many vegans in
developing countries, and they don't get B12 deficiency, so it
must be OK. It is then amusing to watch their face when they hear
the actual source of their B12. Hint: it isn't a nice thought, and
definitely is not for the squeamish. See the "dietary sources"
section of http://www.vegsoc.org/info/b12.html

Clearly B12 and calcuim can be safely obtained from "artificial"
supplements, but they can be difficult to obtain them directly from
food. If in doubt, use the USDA nutrient database to calculate
the amount of an ingredient that someone would have to eat to
get their RDA.