Ashley Tisdale only ''allows'' herself to eat carbohydrates ''once a week''.

The 31-year-old actress has admitted she has had to drastically change her diet because she has recently discovered she has ''food sensitivities'', which has led her to cut out dairy as well as stodgy breads and pasta from her eating plan, although she will treat herself now and again.

Speaking to PEOPLE about her new clean eating, the blonde-haired beauty - who is known for playing the role of Sharpay Evans in 'High School Musical' - said: ''I recently found out what my food sensitivities are, so I had to cut dairy out and certain other foods that weren't good for me.

''Also, as much as I love carbs I cut them down a lot. I allow myself to have them once a week.''

The New Jersey-born star also drinks ''plenty of water'', and believes staying hydrated and getting enough sleep are essential for flawless skin.

She added: ''Drinking plenty of water and sleep are my biggest beauty tips. Treat your body how you treat your skin and you will always feel good.''

Ashley has her own beauty and skincare line titled Illuminate by Ashley Tisdale, but the star believes feeling good is not about a person's appearance but about their internal character.

She explained: ''I have a make-up line, Illuminate by Ashley Tisdale, and yes it's easy to put make-up on and go out, but true confidence comes from within.

''For me, it's all about feeling good.''

And Ashley has revealed her cosmetics collection in partnership with BH Cosmetics was a complicated process.

Speaking previously about her capsule, she said: ''I'm someone who loves make-up - I love doing my own make-up and getting my make-up done - and I had specific ideas for what I wanted the palettes to look like so they would represent me.

''It was good that I did [go in early] because the first time they printed it, it was tad off, so they did another print. There is a lot that goes into every detail.''