'This does not come naturally': Molly Sims reveals the secrets to her hard-earned bikini body

Model Molly Sims has stripped off to flaunt her fabulous bikini body on the cover of America's Shape magazine.

But in a refreshingly candid interview, the 38-year-old, who is known for her Sports Illustrated swimsuit covers, admits her incredible physique is the result of more than just good genetics.

While many super slim celebrities claim they can eat whatever they want and never work out, the model puts her body down to hard work.

'This does not come naturally,' admits the Southern-born belle of her cover-worthy physique.

'I have to work out 60 to 90 minutes at least five days a week and stick to a high- fibre, low-calorie eating plan.'

Wearing a lime green bikini with a blue cover-up, Sims explains that until a couple of years ago, her fitness routine was erratic and she was tired of dieting.

Finally, after constant weight fluctuations, she made a resolution that changed her life.

'I wanted to be consistent with my exercise, so I committed to working out for 30 days in a row, no matter what,' she says.

'For an hour every day, I did something. I was on the elliptical or the treadmill, and if someone asked me to go to a class -- whether it was spinning, boxing, yoga, you name it -- I went.'

 'By the end of the month, I felt so good, I just kept going. I didn’t want to lose my momentum.'

One of her biggest pieces of advice is for people to completely commit to an exercise routine -- even if they only have 15 minutes. '

Whether it's time on the treadmill or an upper-body routine, you just have to get that heart rate up and keep it there,' Sims says.

The model recently said 'I do' to movie producer Scott Stuber, 42, at the Frank Cafaretta Vineyard in Napa Valley in front of family and friends.

Stuber has produced such films as Love and Other Drugs and The Break Up, popped the question to Sims in May.

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