Serena said she's cut down on eating chicken and fish and is eating more raw foods, as does Venus, who adopted the change to help her body cope with Sjogren's syndrome, an autoimmune disease that can cause fatigue and joint pain.
Although the new diet has been a big change for Venus, Serena said it hasn't been that big a deal for her.
"I've always been a better eater than her, even though I'm a lot, lot thicker," she said, laughing during a recent phone interview.
Serena said since she lives with Venus, she is mindful to eat foods that won't tempt her sister.
"I don't want her to come home and see a piece of chicken and be like, 'Oh, I want it,' and she can't have it. It would be like a stumbling block for her," she added.
Both Serena and Venus have been back on the tennis court recently after dealing with health issues.
"I'm looking forward to playing, and just playing and being healthy; I haven't really been healthy in a few years, and I'm just really looking forward to having a chance to play," she said. "I think right now I am at 100 percent ... I'm really looking forward to continuing this and continuing to be healthy."
Besides her excitement for upcoming Grand Slams and the Olympics, Serena said she's also still focused on her side ventures, which include an upcoming appearance on the TV show "Drop Dead Diva;" her nails (she's a licensed manicurist and has a nail polish line); her clothing company, Aneres (she said it's relaunching online next year); and business school, just to name a few.
She's also part of a new venture with LeBron James, Amare Stoudemire, Chris Paul and recording artist Pitbull to promote Sleep Sheets, which bills itself as a natural sleep aid. Serena said she's had trouble sleeping for years because she's "constantly on a natural high, high on life and happy, happy, happy and working."
She said her sleep difficulty was so bad one year it affected her at the Australian Open.
"Several years ago before like the finals, I couldn't sleep, and I had to take something to relax and make me go to sleep," she said. "It was obviously a pharmaceutical thing, but I physically couldn't sleep, and the only thing with that is that it slows you down the next day."
She still won the trophy.
"I did, but I was a little sluggish," she said, laughing. "It's nothing that I ever want to do again. I can't put the finals of the Australian Open on the line because I can't sleep."