MILAN -- Venus Williams will make her comeback Wednesday in an exhibition match against her sister Serena in Colombia, two months after pulling out of the U.S. Open because of an immune system disease.

Venus told Thursday's Gazzetta dello Sport that she has changed her diet to include more vegetables after being diagnosed with Sjogren's syndrome, which can cause fatigue and joint pain.

After playing Serena in Medellin next week, Venus will join her sister against Italians Francesca Schiavone and Flavia Pennetta in another exhibition match Dec. 3 in Milan.

Serena hasn't played since losing to Samantha Stosur in the U.S. Open final in September.

"I did a lot of medical therapy and a serious evaluation of my diet to understand which foods help control the symptoms better," Venus Williams told the Gazzetta, which is sponsoring the Milan exhibition.

"And that's why I've completely changed my diet and filled it with a lot of vegetables," she said. "In the meantime, I've continued to keep myself fit with tennis and in the gym. I'm very confident in my progress."

Venus' ranking has fallen to No. 103 because of injuries. She is planning to return to the WTA Tour in January at the ASB Classic in Auckland, New Zealand.

"The London Olympics are a big goal," the five-time Wimbledon champion said. "I would like to continue playing at my best level. I love tennis and the racket seems like it was made explicitly for my hand.

"Within the next 12 months, I'm expecting to get back to the top of the rankings in singles and doubles. I want to play all year long. I've still got a lot of work to do but it doesn't scare me -- I'm used to it."

Copyright 2011 by The Associated Press