R.S.V.P. P.S - No Gluten, Fat or Soy, Please - NYTimes.com Coco Myers, a writer, prepares a salad in her kitchen in East Hampton, N.Y. She keeps gluten and lactose out of her diet. The offending object? A footlong loaf of bread, stuffed with savory cheese, purchased at a beloved Italian bakery and presented with pride at a recent potluck meal. "This bread is delicious," I crowed. The kitchen went quiet. You'd think I had offered up a bouquet of poison ivy. One guest said she was gluten free. Another didn't consume milk products. The mood lifted only when someone else arrived with a large bowl of quinoa and lentils. It's becoming harder for Americans to break bread together. Our appetites are stratified by an ever-widening array of restrictions: gluten free, vegan, sugar free, low fat, low sodium, no carb, no dairy, soyless, meatless, wheatless, macrobiotic, probiotic, antioxidant, sustainable, local and raw. Though medical conditions like celiac disease and severe allergies have long relegated a small percentage of diners to rigid diets, more and more eaters outside this group appear to be experimenting with self-imposed limits, taking a do-it-yourself, pick-and-choose approach to restricting what they consume. Some group-dining devotees say they are happy to adjust as the occasion demands. In April, Coco Myers, a writer who avoids gluten and lactose, invited a fish-averse friend to a dinner party in East Hampton, N.Y., hosted by a couple who don't eat red meat. A few days earlier, the hostess (Scott O'Neil, a painter and an amateur cook, who had been planning a seafood stew) e-mailed Ms. Myers to ask about problem foods. Sometimes I go to dinner parties, and you just deal with what you get, right? Ms. Myers recalled. But she put it out there. So she compiled a dietary no-fly list: no fish, no gluten, no lactose. Ms. O'Neil was up to the challenge. "Nowadays I always ask, because there's so many things people don't eat," she said. She swapped the stew for a mixed grill with chicken, scallops, salmon and tofu, rounding it out with rice, an asparagus-topped salad and an upside-down rhubarb cake. Joanne Heyman, who owns a consulting firm in New York, thinks that stories like this illustrate just how much "the locus of responsibility has moved from the eater to the hostess." Ms. Heyman, a former vegetarian, said that she recently organized an invitation-only business dinner for two dozen people. On the day of the event, she started getting last-minute notes from guests saying they were vegetarian, vegan or gluten free. "The distinction is not that people have restricted diets," she said. It's their attitude about whose responsibility it is to meet their dietary needs. But where are all of the atomized eating habits coming from? Do these diners have anything in common, apart from ownership of single-serve Tupperware? Unlike the diet fads of yesteryear (Atkins, Zone, South Beach and countless others), many contemporary eating styles speak directly to values and virtues, aiming to affirm your ethos rather than nuking your love handles. Today's restricted eaters are prone to identity-driven pronouncements along the lines of "I'm gluten free." (It's worth nothing that, back in the aughts, no one declared "I'm Atkins!" Except, quite possibly, Dr. Robert Atkins himself.) Consumers seem to be building self through sustenance, adjusting their appetites to reflect independence and moral character. In numerous interviews with restricted-diet adherents and those who study and feed them, control and identity were two common themes on everyone's lips. "It's an alternative way of finding an identity in a place where identity is increasingly uncertain," said Richard Wilk, the director of Indiana University's doctoral program in food studies. So much of our lives are completely out of our control. You can go to college and not get a job. You can do an internship and not get a job. The economy takes some new tack every 15 minutes. Meredith Yayanos, a musician and a founder of the alternative culture magazine Coilhouse, adapts her diet to influence her mood. "I love the idea that there's a mix and match going on," she said. Ms. Yayanos first dropped gluten, sugar and carbs on a friend's advice after being mugged at gunpoint, a trauma that left her fending off panic attacks and depression. "Within 48 hours, it felt like a thick layer of gauze had been pulled off my brain," she recalled. Now Ms. Yayanos revisits that diet whenever her mood drops. She's noticed her friends experimenting with food, too, essentially "hacking" their bodies, tinkering with different fuels to reap feelings of clarity and energy.