Nicky Hilton stays slim by walking.

The 31-year-old fashion designer - the sister of Paris Hilton - says she avoids taking unnecessary car journeys in New York to keep in shape and believes you can stay fit by climbing stairs rather than wasting hours in the gym.

Speaking about her new fashion book '365 Style', she said: ''To not add weight, I walk not take taxis. Use stairs instead of gyms. If anyone's fat, avoid prints. Try oversize boy stuff. Nothing constricting. Hide the bad body part. Do navy, dark colours. Got great legs, accentuate with short dresses. Super-skinny? Layer.''

Nicky also revealed she has a yearly clear out of her wardrobe and gives her unwanted clothes to her cousins who are delighted to be handed her designer garments.

Speaking to the New York Post newspaper, she said: ''My 'Spring Cleaning' chapter explains I clear out yearly. Female cousins get my hand-me-downs that don't fit anymore. I save special sentimental ones, like what mom gave me.''

Nicky - who got engaged to British banker James Rothchild this summer - has dedicated a chapter in the book to her mother Kathy, whom she thanks for teaching her so much.

She said: ''One chapter called 'Mom Knows Best' is stuff she taught me about life and style.''