There are many scriptures that tells us not to eat garlic:-
palandu lasunam sigrum alambum grjanam palam
bhunkte yo vai naro brahman vratam candrayanam caret
(Padma Purana, Brahma Khanda 19.10, spoken by Suta Gosvami)
O sages, one who eats garlic, onions, sigrum (a kind of plant), turnips, bottle gourd and meat, that person should observe a candrayana fast.
vrntakam jalisakam kusumbha smantakam tatha
palandu lasunam suklam niryasan caiva varjayet
grjanam kinsukan caiva kukundanca tathaiva ca
udumbaram alavun ca jagdhva patati vai dvijah
(Hari Bhakti Vilasa 8.158,159, from Kurma Purana)
One should not eat eggplant, banana leaves, sunflower leaves and asmantaka leaves, onions, garlic. One should not eat sour gruel (a thin watery pouriage) or the juice of the tree. One should also give up turnips and beetroots, carrots, kinsuka, forest figs, and white pumpkin. If the twice born persons eat these things, they all become fallen.
Manu-samhita:
5.5. Garlic, leeks and onions, mushrooms and (all plants), springing from impure (substances), are unfit to be eaten by twice-born men.
5.19. A twice-born man who knowingly eats mushrooms, a village-pig, garlic, a village-cock, onions, or leeks, will become an outcast.
By the way, can anyone explain to me what twice-born means.