Man of Flab RUSSELL CROWE back to chug-a-lugging beers, smoking “fags” and cramming greasy fries into his mouth after doing the Krypton crawl of health.

The 49-year-old Os­car winner has dumped his healthy lifestyle in favor of beer and ciga­rettes, a close pal told The ENQUIRER.

“He had a physi­cally demanding role in ‘Noah,’ but since he finished that in No­vember, Russell has let himself go,” revealed the source.

“He’s totally aban­doned his diet and he’s smoking up to two packs of cigarettes a day.

“Russell might love talking and tweeting about his fitness work­outs, but when it comes to slimming down, he never seems to be able to get it together.”

Crowe managed to whip himself into shape to play Jor-El, Superman’s father from the planet Krypton, for the new movie “Man of Steel.”

But when the 5-foot-11 actor showed up at a promotional event recently, brag­ging that he weighs 245 pounds and was all muscle, “people were cracking up and pointing at his beer gut,” noted the source.

In reality, Crowe is said to be stressed out after filming “Noah” and the upcoming “Winter’s Tale” back to back.

“If he’s not puffing away like a chimney, Russell is stuffing his face with greasy food,” said the source.

“He’s wheezing and coughing all the time.”

The “Gladiator” hunk is also struggling to patch up his marriage to actress Danielle Spencer, the mother of his two young sons.

“Russell’s tried every­thing to win Danielle back, but so far no luck,” said the source.

“They’re still sepa­rated, and there’s no doubt it’s contributed to his refusal to curb his bad habits.”

But oddly enough, the Aus­tralian actor still likes to boast about his fitness.

“He’ll be stuffing his face with french fries between drags on a cigarette and talking about how he can do 50 push-ups on his knuckles,” said the source. “It’s as though he thinks that talking about working out makes people believe he’s actually doing it!”