Besides high quality protein, a strict vegetarian diet may also at risk of
1)
Zinc and iron deficiency
2)
Vitamin D, A(conditional) and B12 deficiency
3)
Over consumption of caborhydrate (like your friend;s case) which would lead to obesity -> X-syndrome and eventually diabetes, heart problem and cancer.
4)
DHA (omega 3 fatty acid) defiency
I believe The risk of deficiency can be significantly minimized by going Lacto-ovo ( organic egg and dairy product) or adding deep sea fish in the meal plan.
Based on my personal disastrous experience on 3 months vegan diet, i would encourage all aspiring vegans to consider cheating on range fed animal food now
at least a few times a week.
The above is just my personal opinion ..