Until recently, the idea of vegetarian food was an all-or-nothing affair.

But lately, the line between those who eat meat and those who don't has gotten blurred: Concepts such as flexitarianism and Meatless Monday are gaining serious traction.

And they owe their popularity in large part to the most outspoken meat lovers around: chefs.

Mario Batali gave the movement legs last year when he started offering meatless specials at his restaurants on Mondays. Chef John Fraser of New York City's Dovetail followed suit with a week-starting all-vegetable menu.

But now meatless has gone beyond the first day of the traditional workweek: In Philadelphia, Meritage Restaurant prepares an elegant Tuesday-night vegan prix fixe. In Healdsburg, California, at Cyrus restaurant, multicourse paeans to the garden share equal billing with traditional meat-and-fish-filled tasting menus on a nightly basis.

In Las Vegas, Wynn Resorts recently added vegan options at all the restaurants in its two casinos--even its steakhouse, SW, where grilled royal trumpet mushrooms now have a place on the menu.

Driving the trend forward again, Batali's new Italian Food emporium, Eataly (pictured), has a dedicated vegetarian restaurant, Le Verdure, that lets diners veg out any time. Chef Fraser, too, is rumored to be opening an all-vegetarian outpost in the near future.

Pork belly, watch your back.