Melbourne: Venus Williams has made the dietary leap from steak lover to raw vegan, but admits that in times of weakness she is a “cheagan.” That’s Venus-talk for a cheating vegan.

“If it’s on your plate, I might get to cheat. If you’re sitting next to me, good luck. You turn your head once and your food might be gone,” Williams said, in good spirits after starting her Australian Open campaign on Monday with a quick 6-1, 6-0 win over Galina Voskoboeva.

“I think it’s pretty well known I’m a cheagan,” the seven-time Grand Slam winner said, laughing. “I’m not perfect, but I try.”

On her website, the 32-year-old American refers to this phase of her life as “Venus A.D.” — Venus After Diagnosis.

Food is not the only difference between then and now, but it is one of the big lifestyle changes Williams has made since being diagnosed in 2011 with an immune system illness that had caused her years of mysterious symptoms like shortness of breath, fatigue and muscle pain.

Williams went public with her illness after withdrawing from her second-round match at the 2011 US Open and then took seven months off tennis, skipping last year’s Australian Open as she learned how to manage the disease known as Sjogren’s Syndrome.

Her website says Williams’ vegan diet is designed to decrease inflammation in her body and reduce the energy-sapping symptoms of the disease “by not overloading her body with excess calories, pesticides or sugars.”

“No more of her favourite cherry pies, as sugar is strictly forbidden,” the website says, adding that Williams has also changed her training regimen to allow herself more days of rest.

Her comeback has been impressive. Williams had the biggest jump of any of the top players in 2012, moving from outside the top 100 to finish the year at No. 24.

“She’s back and she’s fiery!” the announcer told the crowd as the 25th-seeded Williams warmed up on Hisense Arena, the second of the main show courts at Melbourne Park. Fans welcomed her back with extended applause and cheers.

Playing with power and determination, Williams took command of the match early with a steady stream of winners and powerful serves.

She served two back-to-back aces — both over 180kph — to take a quick 5-1 lead and then broke to win the first set in 31 minutes.

The next set went faster. Williams didn’t drop a game, wrapping up the match in an hour flat with a beautiful backhand passing shot.

“Obviously it’s nice to spend less time on the court, and not be in long sets,” Williams said after the match. She said she was happy with match statistics that included a first-serve percentage of 70 per cent. She also took advantage of six of 11 break-point opportunities.

“I don’t think my opponent quite got the hang of, you know, it’s hard to play the first match in a major, first thing of the year, and that can be a lot of pressure.” Williams said about the 80th-ranked Voskoboeva of Kazakhstan. “I did my best to just close it out.”

At 32, Williams is a veteran on the women’s circuit. This is her 13th Australian Open and her 58th Grand Slam tournament.

She is regularly asked when she plans to retire, and routinely says not yet. Despite her star power, Williams has not produced the results lately that she did as a young star. She hasn’t made it past the fourth round of a Grand Slam since the 2010 US Open.

It’s been a decade since Williams’ best showing at the Australian Open, which came in 2003 when she lost the final to her younger sister, Serena, who is a favourite to win this year in Melbourne. Still a powerful pairing, the sisters won a gold at the London Olympics in doubles.

Serena cheered on her sister from the stands on Monday. The younger Williams won Wimbledon, the US Open and an Olympic gold in 2012.

Now that the elder Williams sister is back on the tour and feeling fit, she said she hopes to extend her career - which started in 1994 - into a 20th season.

“Yeah, trying to celebrate the 20th anniversary,” she said, smiling. She reflected on her illness, which she said has helped her “to focus on the things I can accomplish and not to think about the things that I can’t do.”

She also reflected on her career, and the difference between her teenage mentality and now.

“When you’re a young person, you just don’t think it’s ever going to end, and you’re on top of the world,” Williams said. “Now, I realise, all these opportunities, I try to make the best I can of them.”

Her focus for now remains on tennis, starting with a second-round match against Alize Cornet of France and possibly a third-round match with reigning French Open champion Maria Sharapova, who is ranked No. 2.

“I love the game,” she said, “and while I’m here, I’m going to go for it.”