SPEEDO. Let's be honest: The mere mention of the word makes all American men cringe. It conjures up the horrors of mandatory high school swimming class or hirsute men tanning their bulging bellies along the French Riviera, all but turning your pricey Eurozone beach holiday into a tawdry visit to a near-nudist colony.

Mainly, this is because almost no one looks good in a suit of this size, and I imagine I am no exception. Like you, I am a man of these times, and with that comes responsibility. I hit the gym when I can, but most of my exercise comes from chasing around two young children—or sweating over commas. My job as an editor can lead to long hours in the office and obligatory drinks or dinner afterward. I am, to be honest, at my best in a single-breasted blue suit in which the only skin I show peeks out below my cuffs and above my collar. When swimming attire is called for, I likewise prefer something that leaves more than a little to the imagination.

Almost no one looks good in a suit of this size.

Which is all the more reason to admire Alex Breaux, who, as the star of the off-Broadway play Red Speedo, had to stand in front of an audience of 200 for 80 minutes, eight times a week, wearing nothing more than a banana hammock—which he wasn't all that into, either. "I'm not an exhibitionist," the 30-year-old actor says. "I like wearing clothing in public. That's kind of my go-to."

For the role—he played Ray, an elite swimmer entangled in a possible doping scandal on his way to the Olympic trials—Breaux had to put such misgivings aside, donning his wee costume without fear. "My character is extremely confident, so if I'm feeling even a little self-conscious onstage, the audience is going to sense it and I'll lose them."

Red Speedo had the potential to be the actor's breakout role, the kind of showcase that casting directors flock to and future biographers recall with great relish. Or the whole thing could've been an awkward, flabby disaster. Breaux knew his fate rested on his own abs.

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Joan Marcus
Breaux on stage during a performance of Red Speedo.

From initial casting to first curtain, Breaux had less than five months to transform his six-foot-three, 185-pound frame into something that could pass for a world-class swimmer's body. And since this was off-Broadway and not Hollywood, he had to do it on his own dime.

"I tricked myself into thinking that Red Speedo was a Marvel action movie and I was being paid millions of dollars, with access to nutritionists and trainers," he says, echoing Chris Pratt's exact sentiment when asked about his motivation for shedding 60 pounds and bulking up for 2014's Guardians of the Galaxy. "But I couldn't afford any nutritionists. I couldn't afford trainers. I had to figure it out and get by solely on my own willpower."

Breaux was no stranger to the gym: A former wide receiver at Harvard, he's a fitness freak who teaches spinning classes in between acting gigs and auditions. But it was Jake Gyllenhaal, whom he'd met while costarring with his sister, Maggie, in the 2014 Broadway revival of Tom Stoppard's The Real Thing, who provided the real inspiration.

"Jake got shredded in Southpaw," says Breaux, referring to Gyllenhaal's famous body transformation for last year's boxing drama. "Like, more shredded than I've ever seen an actor get. And so I looked up his program and found out what he did to get there. Every day, he'd run eight miles and do 100 pull-ups, 100 dips, 100 push-ups, then 500 to more than 1,000 sit-ups. That was his base. So I thought, Okay, that's a good starting place."

"He'd run eight miles and do 100 pull-ups, 100 dips, 100 push-ups, then 500 to more than 1,000 sit-ups. I thought, 'Okay, that's a good starting place.'"

Another key component was changing not just what but also when he ate. For more torture, Breaux turned to a diet called intermittent fasting. "You have to eat all your food for the day within an eight-hour window. I would eat twice, around 10:00 A.M. and 6:00 P.M.—salads without dressing; lean meats like chicken and salmon—and I wouldn't eat at any other times. Your body enters a fat-eating state—I'm probably oversimplifying it—but that helped define my abs a lot more."

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By the time the curtain lifted for his first preview performance, he'd cut his body-fat percentage in half. He'd achieved the sort of total body transformation that Gyllenhaal and Breaux's other like-minded acting heroes had pulled off. "So many of the actors I really respect are the ones who throw themselves into roles, like Jake, Daniel Day-Lewis, Christian Bale," Breaux says. "They really had to change their body type, and the audience rewarded them for it."

Body-Transformation All-Stars 

Christian Bale

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Following a strict diet of apples, water, and coffee, Bale dropped over 60 pounds to a scant 120 to play a madman in 2004's The Machinist; just months later, he carbo-loaded and weight-trained his way past 200 to fill out the suit for Batman Begins. A more traditional coffee pairing—doughnuts!—helped him become a fat and happy 228 for American Hustle in 2013.

Jake Gyllenhaal

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For his role as an adrenaline junkie in 2014's Nightcrawler, Gyllenhaal chewed gum at mealtimes and often ran the 15 miles to set; he shed 30 of his 180 pounds. He turned to food again—and grueling daily workouts with former pro boxer Terry Claybon—to pack on 15 pounds of lean muscle to enter the ring in 2015's Southpaw.

Robert De Niro

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De Niro reportedly dropped 30 pounds from his already thin frame to play deranged cabbie Travis Bickle in 1976's Taxi Driver. Four years later, for Raging Bull, he bulked up to a muscular 165 to embody real-life boxer Jake LaMotta at his fittest—and then, aided by a food tour of Italy, added another 60 pounds to portray him at his fattest.

The 10% Improvement Plan

We asked elite trainer Ron Mathews, who's helped shred Hollywood heavyweights like Hugh Jackman and Joe Manganiello, to modify Breaux's regimen for the time-crunched, considerably more clothed Esquire everyman.

Gyllenhaal's Thing 

Cut down the rep ranges of pull-ups and crunches to doable sets of 5, 10, 25. If you can't do pull-ups (a lot of guys can't, at least with good form), try lat pull-downs or rows. Every rep you do is more than none. Fewer reps will take the total workout time down a lot, too.

Fast Times

Lower total daily calories by 500 or so. Eat small, nutrient-dense meals of unprocessed foods—lean proteins, vegetables, whole grains—and go to bed on an empty stomach. Limit booze to once a week. Liquor has fewer calories per serving than beer and wine.

Ugly Truth 

It would be great if you could work out just twice a week and magically look a lot better. But if it worked that way, all of us would be running around with six-packs. Exercise four times a week using good form and clean up your diet, and you'll see a 10 percent improvement.