LOS ANGELES (Reuters) - Chipotle Mexican Grill Inc, known for its indulgent burritos, is battling a "Chubby Chipotle" ad campaign from the food industry group whose "Nanny" ads helped sink New York City's ban on super-sized sugary drinks.

The Center for Consumer Freedom's full-page advertisement in Thursday's New York Post depicts a smiling, shirtless, overweight young man flexing one arm and resting the other on his ample tummy.

The text under the "'Chipotle' Healthy" headline reads: "Eat two 'all natural' Chipotle burritos a week and you could gain 40 pounds in a year."

It urges consumers to find out more at ChubbyChipotle.com, a site that calls the company's executives "fast food hypocrites" for claiming that Chipotle's menu is GMO-free and for bending their own rules on "no antibiotics ever".

The CCF, founded by powerful lobbyist Rick Berman to fight smoking bans in eateries, said it is supported by restaurants, foundations and individuals. It declined to name the company that funded the latest Chipotle campaign.

The ad is "a deliberate effort to smear us," Chipotle spokesman Chris Arnold said.

"These are agenda-driven people who are being backed by unknown parties. It doesn't matter who they are as long as they pay," Arnold said.

Public health experts have warned that Chipotle dishes loaded with cheese, sour cream and guacamole can approach or exceed daily recommended allowances for calories, sodium and saturated fat.

The company said it is different from other chains because diners choose what goes into each Chipotle meal.

The CCF ad is the latest blow against the popular company.

A California woman earlier this week accused Chipotle of false advertising related to its claim that it had removed genetically modified organisms, or GMOs, from its food when many of its beverages contain a sweetener made with genetically modified corn.

Arnold called the lawsuit "meritless" and "filled with inaccuracies." He added that Chipotle has been transparent about GMOs in beverages.

Chipotle won a loyal following by offering meat from animals that have never received antibiotics. Still, critics are quick to note that it serves conventionally raised chicken when such supplies fall short. And, Chipotle recently cited tight supplies for its decision to allow a new pork producer to use antibiotics to treat animal illness "only when necessary."

The CCF in 2013 fought then-New York City Mayor Michael Bloomberg's proposed obesity-fighting sales ban on large sugary beverages by depicting him as a nanny.

(Reporting by Lisa Baertlein in Los Angeles; Editing by Bernard Orr)