Someone in the group is scrolling a restaurant’s menu from the couch, phone tilted sideways, hunting for any mention of tree nuts or shellfish. For restaurant operators already squeezed by food costs and thin margins, that’s a lot of business disappearing before anyone on staff knows it was ever in play. That disclosure reaches more people than restaurants might expect, because the person deciding where the group eats isn’t always the one with the allergy. For restaurant operators, one of the biggest losses is the guests who considered dining with them but ultimately chose another restaurant or ate at home. For restaurants willing to make allergen information clear, the $12.6 billion is still there to be won.