Just host a dinner party (I dare you), and you’ll realize how fractured American dietary preferences have become. You’ll likely be bombarded with news of your guests’ gluten-free, dairy-free, or vegan lifestyles. Some may have gone paleo or decided to quit sugar.

Such “food tribes” are nothing new. “Humans have a seemingly innate desire to belong, and food preferences have always been one way to do that,” notes Marion Nestle, PhD, a nutrition professor at New York University. What is new, say dietitians, is just how many people are restricting their diets—not as a fleeting weight loss tactic, but as a way of life.

According to market-research firm NPD Group, one in three U.S. adults minimizes or eliminates gluten intake. Five percent of Americans eat vegetarian by eschewing meat, fish, seafood, and poultry, and 2.5 percent are strictly vegan (no animal products, including eggs and dairy), according to a Harris Poll commissioned by The Vegetarian Resource Group. On the flip side, the carnivorous paleo diet topped the list of most Googled diets in 2013, converting an estimated 1 million to 3 million Americans, according to research by The State University of New York (SUNY).

Experts in each tribe point to studies suggesting these eating plans may reduce risk of chronic diseases like diabetes and heart disease plus gastrointestinal problems and argue that because they emphasize whole foods—an undeniable plus—they beat typical American fare.

But the tribes are not above criticism. Judy McLean, PhD, a nutrition professor at University of British Columbia, says there’s “so much restriction going on” that she’s seeing vitamin deficiencies she hasn’t tracked in years. “Avoid dairy and wheat and you cut out a lot of fortified foods,” she says. Adds Nestle: “One of the classic tenets of adequate nutrition is variety in food intake. So eliminating entire food groups means you have to be very careful to replace missing nutrients.”

What’s the rationale behind America’s top food tribes? Do they really make people healthier? Are they here to stay? Here’s a look.