The 42-year-old former model - who has six-year-old daughter Beatrice with ex-husband Sir Paul McCartney - would love to have another youngster to look after, but thinks the world is "too overpopulated" to want to get pregnant again.
She told the Daily Express newspaper: "I wouldn`t have another child because the world is already too overpopulated. But I might adopt one."
Charity campaigner Heather - who has her own vegan restaurant, V-Bites in Brighton, South East England - also spoke of how her young daughter is already following in her famous mother`s footsteps when it comes to animal rights.
She said: "She goes up to people in restaurants and says. -You know that`s a baby cow?` People must think that is what I tell her at home, but it`s not."