SOME relationships run aground on the perilous shoals of money, sex or religion. When Shauna James’s new romance hit the rocks, the culprit was wheat.

“I went out with one guy who said I seemed really great but he liked bread too much to date me,” said Ms. James, 41, a writer in Seattle who cannot eat gluten, a protein found in wheat, barley and rye.

Sharing meals has always been an important courtship ritual and a metaphor for love. But in an age when many people define themselves by what they will eat and what they won’t, dietary differences can put a strain on a romantic relationship. The culinary camps have become so balkanized that some factions consider interdietary dating taboo.

No-holds-barred carnivores, for example, may share the view of Anthony Bourdain, who wrote in his book “Kitchen Confidential” that “vegetarians, and their Hezbollah-like splinter faction, the vegans ... are the enemy of everything good and decent in the human spirit.”