SAN FRANCISCO (Reuters) - About 25 overweight protesters picketed a San Francisco fitness club Monday to protest against a new billboard claiming that, when space aliens finally do encounter humans, "they will eat the fat ones first." "I can`t believe that a gym would have so little concern about the health of people," said protest leader and author Marilyn Wann, whose book "Fat!So?" seeks to challenge social stereotypes about fatness. "I represent the 97 million Americans who are fat. We`re 55 percent of the population, it`s really not safe to alienate us because we might just sit on someone," Wann told KCBS radio. The protesters were angry at 24 Hour Fitness for a new billboard above a city freeway that depicts a leering, alien face and carries the message "When they come, they will eat the fat ones first." The fitness chain, which runs gyms throughout the western United States as well as in Asia and Europe, said it had not meant to offend anybody with the advertisement. "We all know how hard it is to lose weight," the company said in a written statement. "Sometimes humour helps make things easier, and can even be motivational."