File photo: The 36-year-old gave birth to her first child, Alexis Olympia, in September and took more than a year off. Picture: AP

London - Serena Williams has opened up about how she stopped breastfeeding her daughter after six months because it caused her to gain weight.

The seven-time tennis champion spoke about the emotional decision to give up nursing as she prepared for her Wimbledon comeback.

She said the old adage that new mothers lose weight by breast feeding is false and that she actually dropped 10lbs (about 4.5kg) almost immediately after stopping.

"It was interesting because all these articles over pop culture, you hear when you breastfeed you lose weight, and you’re so thin," she said, adding: "That wasn’t happening to me... I didn’t know that it wasn’t true."

The 36-year-old gave birth to her first child, Alexis Olympia, in September and took more than a year off.

She said she planned to stop breastfeeding in January but then continued until April before being advised by her team to stop in order to get into shape.

The mother of one said: "I was vegan. I didn’t eat sugar. I literally have my chef total vegan.

"Not French fry-eating vegan. Totally eating completely healthy. I wasn’t at the weight that I would have been had I not." She added: "For my body it didn’t work. No matter how much I worked out, no matter how much I did, it didn’t work for me."

Williams said once her daughter was six months old she finally felt she was able to stop nursing. "Then it was just emotionally letting go," she said.

"That was a different thing. I literally sat Olympia in my arms, I talked to her, we prayed about it.

"I told her 'Look, I’m going to stop. Mommy has to do this I cried a little bit, not as much as I thought I would. She was fine."

She added: "After that, like literally I lost ten pounds in a week. It was crazy. I just kept dropping... that’s when I learned that everything was different."

Williams, who wore a stunning catsuit at the French Open in tribute to mothers who have had difficult pregnancies like her, added: "I wanted to say that so women out there know that’s not true.

"Everyone takes things different. I think it’s important for us to share that message."