As my arrest and subsequent upcoming trial for identity theft shows, it's really not easy being Kate Beckinsale.

Whether she's starring in the Pearl Harbor movies, standing around confused in the Underworld movies or taking on the impossible task of feigning attraction to Adam Sandler in the 2006 movie Click, this British actress generally brings the acting chops, and she always looks good doing it.

Starting her movie career all the way back in 1993 with Much Ado About Nothing, K-Becks is now 45 years old, but you wouldn't know it by looking at her. Okay, don't look too long; don't be a creep. Kate Beckinsale keeps her body in tip-top shape by adopting the ketogenic diet, and she's got a really neat trick for staying as sexy as she does.

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If you were to come across Kate Beckinsale at the airport and happened to open up her suitcase, you'd find a stick of Kerrygold butter amongst all of her various things. If you were to ask her about it, she might say something like "hey - weren't you the guy who tried to steal my identity?" but more likely, she'd explain that the butter wasn't for spreading bread.

At that point, it might be worth asking Kate Beckinsale for coffee, and if she cautiously agrees, then you'll get to see the reason Kate Beckinsale always travels with butter. She'll stir it into her coffee alongside some oil, making something called the Bulletproof Coffee - whose advocates say it has an impact on both your energy levels and brain function.

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Kate Beckinsale, it appears, is one of those advocates. But how did she come across the concept of Bulletproof Coffee? It turns out, you have to go all the way back to 2004, when Kate Beckinsale was preparing to star in Pearl Harbor. “When I did Pearl Harbor they had me on a very strict low-fat diet,” she recalled.

"I remember my mum coming and visiting me and going, ‘You look so old.’ I was 24 and I had lines on my face because I didn’t have enough fat. And so now, I remember very early on meeting a great nutritionist and they said, ‘One day everyone is going to say don’t eat low-fat margarine or they are going to say eat butter or eat olive oil.’ "

Beckinsale said it took her a long time to see the effects of her new buttery latte, but eventually, she noticed that her skin looked a lot healthier, saying she noticed the difference "in a week or two". "If I’m going from one city to another I’ll put some in my suitcase to make sure I have it. I’m the crazy person traveling with butter,” K-Becks admitted.

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Well, what do you think? Butter in your coffee seems really unhealthy (I actually think there's a joke from the Simpsons about that), but if it works for Kate Beckinsale, why can't it work for you?

Actress Kate Beckinsale reveals why she always travels with a stick of butter