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Has Elle Macpherson discovered the fountain of youth? The stunning model has enviable looks and an insanely toned body. So, what is the 51-year-old's secret?

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Elle doesn't leave home without a pH balance urine tester kit in her handbag.

No, this isn't a joke.

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In an interview with the Evening Standard, Elle said she uses the kit to check the state of her body.

"[The most surprising thing in my handbag is] a pH balance urine tester kit to check that I'm in an alkaline state. I believe that most ailments come from having an acidic body," she said.

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The body's pH value tells you how acidic or alkaline your body is, and many nutritionists believe that having an alkaline body helps defend against sickness and disease.

So, how do you get an "alkaline body?" A lot of leafy greens and exercising. Elle works out six days a week and varies her workouts, but it involves a lot of cardio.

"[My idea of a healthy diet is] consistency and eating three healthy meals a day," she told the London-based paper. "Having said that, red meat, wheat and dairy don't work for me."

Life, it's all about balance.