‘Maybe’ star Isla Fisher is a new mom, but definitely don’t ask!

Isla Fisher didn’t shed her pregnancy pounds through a grueling celebrity-mandated regimen of sweat and starvation.

Ask the Aussie actress about her trim figure since giving birth to daughter Olive in October, and she grins mischievously. She lifts up her filmy, flowered blouse and crows the magic word: “Spanx! You know them? It’s night and day!” Fisher says of her tummy-smoothing undergarments.

Fisher is still nursing and, hence, calorie-counting isn’t a priority as she digs into a jar of M&Ms.

“I really felt like there’s so much pressure on young women in show business. There’s so much body fascism. I don’t buy into any of it. But I do have good genes,” she concedes.

For all her sparkly sociability, Fisher reveals nothing about her relationship with comedian Sacha Baron Cohen, to whom she is engaged, or their life together as parents of Olive.

“Motherhood is my favorite topic in my personal life, but I never talk about it publicly only because I don’t want to draw any attention to her,” says Fisher, 32. “I want to protect her.

“I’m a private person. Talking at all about your personal life opens the door and shines a light on it, and it feels good at the time, because you please the journalist. But at the end of the day, do I go see a movie because I know the private life of the actor in the film?”

Fisher won’t even talk about balancing movie offers with her role as a new mom. “I can’t answer without touching on the most important thing in my life. So, I’m scared to. I’m sorry,” she says.

She will say that work right now “isn’t as big a priority.”

It certainly isn’t for April, the sharp-tongued sprite whom Fisher plays in Definitely, Maybe, opening Thursday. Fisher is Ryan Reynolds’ kooky, cute pal who just might be his Miss Right. Other contenders for the title are Rachel Weisz and Elizabeth Banks.

“I think it’s told from a male perspective, so hopefully guys will go,” Fisher says. “It’s not just one girl in the movie. It’s three. It’s a romantic whodunit.”

To Fisher, April represents a younger version of herself.

“April was very similar to me when I was in my early 20s. She’s free-spirited and apolitical, doesn’t believe in marriage and is desperate to travel the world,” Fisher says. “I was like that. She has this arc and ends up working for Amnesty International, which I totally take my hat off to. I wouldn’t have the strength to work somewhere like that. I’d be crying every day at every crime against humanity that I knew about.”

In her regular life, Fisher is an enthusiastic chef who cooks a mean roasted chicken. She once toyed with being a psychologist. And she’s a movie buff who just saw and fell in love with Juno and its Oscar-nominated star Ellen Page. “It’s all about Ellen. She’s gorgeous,” Fisher says.

The redhead most famous for taming Vince Vaughn’s lothario in Wedding Crashers says she’s getting pickier about what she opts to do, work-wise. Since cannon-balling to fame in the 2005 comedy, she has done dark drama (2007’s positively reviewed but little-seen The Lookout) and goofy comedy (last year’s silly romp Hot Rod, starring Andy Samberg).

“I’m choosy, definitely,” Fisher says. “I’ve made a lot of product in my life that I’m not proud of. I’ve had to work. Now that I’m fortunate enough to get to choose, I’m fussy. Now, I don’t have to make decisions as much from fear. It’s given me freedom.”

Now, Fisher is shooting Confessions of a Shopaholic in New York. She’s “so excited” about being retail addict Rebecca Bloomwood on the big screen. “I loved those books. I’m such a Sophie Kinsella fan. She’s such a talented writer, and it taps into the consumer collective conscience,” Fisher says. “I’ve done a lot of research — a lot of shopping.”

So the obvious question: Is she a big shopper in real life?

“It depends what I’m shopping for,” Fisher says. “My favorite thing to shop for would be bags. I don’t have that many. I believe in recycling — you pass the bags on.”