“Older suits made men look like executive fat cats,” Mr. Jennings said, as he guided me past boutiques featuring brands like Dolce & Gabbana, Zegna and Isaia, to name just a few. “Men today are exercising. They’re more slender. Clothes are showing their physique. Even the classic lines are slimmer.” Mr. Jennings himself looked very fit in a Burberry suit with a trim silhouette, vest and narrow lapels that he’d just bought. “The fabrics don’t change,” he said, pointing to the classic gray flannel of his suit. “But the fit does. If you’re wearing a suit from four years ago, it’s dated.”

What about men who aren’t fit, or are even overweight? “If the suit is well cut, anyone looks better and slimmer than he would in one of those voluminous suits with pleats that tried to cover things up,” Mr. Jennings said.

Men’s wear sales have benefited from a new generation of designers who made their name in men’s clothing: Mr. Ford, formerly at Gucci and now with his own label; Thom Browne, who introduced the retro-schoolboy look; John Varvatos, whose designs highlighted the male physique; and Hedi Slimane, who championed the superslim profile while at Dior Homme and designed Brad Pitt’s wedding suit. While their runway designs may have been too extreme for the average male shopper — “No one’s going to come out of J. Crew looking like a fashion victim,” Mr. Drexler said — their influence is apparent.

“The more mainstream, better men’s wear designers have had to follow their lead,” Mr. Pruitt, the consultant, said. So have the media. In the recent James Bond hit “Skyfall,” Daniel Craig, as an aging but muscular Bond, wears the new look: “The suit is seductively tight, for starters, and moves like a second skin,” Manohla Dargis observed in a film review in The New York Times. The stodgy bureaucrats, by contrast, are in wide lapels. Mr. Pruitt also pointed to “Mad Men,” the Emmy-winning series about a Manhattan advertising agency in the 1960s, as an important influence. “ ‘Mad Men’ made people understand that the slim suit is a cool thing.”

“By contrast, there’s really no excitement in women’s fashion,” Mr. Pruitt said. “There are some beautiful things, but no new designers to speak of, and no must-have items.”

Max Wastler, 31, lives in Chicago, where he writes a blog, All Plaidout, and runs Buckshot Sonny’s, an online sporting goods store, with his business partner, Joe Gannon. He recently acquired his first suit, a made-to-measure model from Oxxford Clothes, named “1220” for its Chicago headquarters address on West Van Buren. Navy, trim-fitting, with a high arm hole, side vents and plain-front trousers, it could easily have come from the “Mad Men” set.

“I’ve been spoiled by the semicustom fit,” Mr. Wastler told me. “It fits perfectly.” Having had no suit in his previous casual wardrobe, he now wears the suit at least twice a week and pairs the jacket with jeans on weekends. Now he wants another. “I desperately want the suit worn by Cary Grant in ‘North by Northwest,’ ” he said. “Dark gray flannel and a perfect fit.”