Venus Williams watches her sister Serena during a semifinal match against Caroline Wozniacki of Denmark at the U.S. Open tennis tournament in New York on?Saturday, Sept. 10, 2011.

Venus?Williams has changed her diet following the autoimmune disease that kept her out of this year's US Open and is hoping the new approach will propel her back to the top of the women's tennis rankings.

"I changed my diet completely, so lots of vegetables," the 31-year-old former world No. 1 told a conference in Qatar on Sunday. "I (altered) my mind frame completely because I was the person who always ate their steak first and their salad second."

The lifestyle change follows her shock withdrawal from September's US Open with Sjogren's Syndrome, a chronic disease where white blood cells attack moisture-producing glands and can cause dysfunction of organs and body systems.

The seven-time grand slam champion suffered with fatigue and swelling because of the illness and has slipped to 103rd in the rankings having not played much this year. "My goal next year is to play a full schedule. It will take some work to get there, but I'm no stranger to hard work," she said.

"I love the game. The racket feels right in my hand and I'm planning on going right back to where I was at the top of the rankings in the singles and doubles sometime within the next 12 months."

Williams's last grand-slam singles triumph was her 2008 Wimbledon crown. Since then, younger sister Serena has won a further five grand slams to take her tally to 13.

Five-time Wimbledon champion Venus said she had no time for anything outside tennis and her business interests. "It's so much fun being single - at some point I'll be mature, but it just hasn't happened yet," she said. "I'm shocked at myself by my inability to settle down and to commit to anything besides tennis and work."

She added she would never date a tennis player. "Those are my colleagues," she said. "Handshake, that's it."