"I don't drink alcohol," she reveals. "I feel [its effects] very quickly, so I've never actually had an entire glass of anything alcoholic."
While Beckinsale has no problem saying no to alcohol, she admits that motivating herself to work out is a little bit harder.
"I start out absolutely dreading it, do an incredibly punishing workout, b*tch about it the whole time and end up feeling 100 percent better when I leave," she says. "Working out is basically nature's antidepressant."
The Underworld star also credits her trainer, Gunnar Peterson, for getting her through the toughest workouts by focusing on family instead of exercise.
"I work out hard with Gunnar five or six times a week. We have loads in common, like our kids," explains Beckinsale, who shares 17-year-old daughter Lily with her ex, Michael Sheen. "During our sessions we have long talks about teenagers, and then suddenly one day I find that my a** is in a lot better shape than I thought it was!"
"Hardcore workouts have really made a big difference in my life," she continues. "I have a lot of internal energy, and intense exercise helps me channel that energy. I find balance by doing a workout that makes me pour sweat. I never was that girl before, but I am now."
Beckinsale will have a lot more time for her hardcore workouts in a few months, when her daughter heads off to college -- and she's not complaining!
ET sat down with the actress earlier this month, where she explained why she's looking forward to having an empty nest.
"It's nice as well because it gives me a little bit more room to write and to do other things that I've not necessarily been able to do," she confessed. "That's obviously changed in the last couple of years because [Lily's] not dying to hang out with me every minute of the day anyway, but I'm pretty excited about it."