Jain dietary restriction reasons from the doctrine that even the smallest and least visible forms of life carry a soul, and that harming them accrues karma regardless of intent. Root vegetables, onion, garlic, potato, carrot and their kind, are avoided because pulling them up kills the entire plant rather than a fruit or leaf that the plant can regrow, and because the earth around the root shelters organisms that the digging necessarily destroys. The same reasoning extends to honey, which is refused because its collection is held to kill or injure bees, and to any fermented food, whose fermentation is treated as a sign of active microbial life within it.
Water and milk are strained before use, a practical extension of the same principle meant to remove any small organism before it can be swallowed unnoticed. Jain monastics carry this furthest, straining water they carry with them and inspecting food closely before eating, while lay Jains generally practice a less exacting version of the same habits in an ordinary kitchen.
The result is a stricter vegetarianism than that practiced by most Hindus and Buddhists who also avoid meat, since it excludes categories of plant food that carry no obvious connection to animal harm at all, and it marks Jain households and Jain owned restaurants as recognizably distinct even within vegetarian South Asian cuisine generally.