media_removed_toofab 2013

Now we know how Kim Kardashian got back into her skinny jeans so fast!

The new mom was spotted over the weekend sporting some skin-tight denim as she went out to dinner at Casa Vega in Sherman Oaks with North West and the rest of her family.

But while she was there, Kim probably wasn't eating too many tortillas -- because she's on a low-carb diet.

After seeing her back in some of her pre-pregnancy clothes, fans took to Twitter to ask how she dropped the weight.

So, while she could have eaten as much guacamole as she wanted at the restaurant, tortillas and chips are off-limits for her new diet.

"She is eating lots of lean proteins, healthy fats like nuts and avocado, carbs, fruits, veggies and cheese," a rep for Atkins told Us. "She wanted to be a healthy, nursing mom and not toxify her milk with her diet or lose weight too quickly. She's been doing Atkins since her doctor approved it at the end of June."

No word yet on if she's getting paid to use their diet plan. 

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