Ahead of the Mutua Madrid Open, Serena Williams said she has cut down on eating chicken and fish, and is eating more raw foods.
The diet change is to support her older sister, Venus, who adopted a different diet to cope with Sjogren's syndrome, an autoimmune disease that causes fatigue and joint pain.
"I've always been a better eater than her, even though I'm a lot, lot thicker," she said, laughing.
Serena said since she lives with Venus in Palm Beach Gardens, Florida, she is mindful to eat foods that will not tempt her.
"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," said Serena, who added that she is healthy again.
"I haven't really been healthy in a few years, and I'm just really looking forward to having a chance to play.
"I think right now I am at 100 per cent."
Besides her excitement for upcoming grand slams and the Olympic Games, Serena said she is also still focused on her side ventures, which include her clothing company Aneres (Serena spelt backwards), which she said is relaunching online next year, and business school, just to name a few.
She is also part of a new venture with NBA players LeBron James, Amare Stoudemire, and Chris Paul to promote Sleep Sheets, which bills itself as a natural sleep aid.
Serena, who faced Elena Vesnina of Russia late in the first round of the Mutua Open on Sunday, said she has had trouble sleeping for years.