Those mom jeans and fat Jessica Simpson pictures are so last year.

The singer ... actress ... whatever she is totally got back into killer shape again and she’s crediting boxing as having her reached her weight loss goals.

There's little doubt that Jessica's bod is rockin' again.

Exhibit A: The flattering black dress she stepped out in Wednesday night for a dinner date with friends in Los Angeles. Gotta give credit where due:

The 2010 version of Jessica Simpson is leaner and meaner!

Jess Tweeted this week: "Boxing changed my life! I have so much energy and it cured my insomnia. Although I don't think I can get out of bed I'm SO sore."

Simpson, whose ex-loves include Nick Lachey, John Mayer and Tony Romo, is also reportedly happy and in love with her new flame, rocker Billy Corgan. Really.

We're glad she's doing better and not sitting around jamming candles in her ear. You can chalk up her big turnaround to boxing at the gym. The only drawback?

"Dear elderly man at the gym," she Tweets. "its hard 4 me 2 keep composure whilst punching at chipmunk speed when ur ball sack spills out of ur wind shorts."

You heard her, naked old guy at the gym. You're on notice.