"It's a little queasy sounding, but there's no place for that material to go, and it makes great radiation shielding," says Taber MacCallum, a member of the team funded by multimillionaire Dennis Tito, who announced the audacious plan earlier this week.
McCallum told New Scientist that solid and liquid human waste products would get put into bags and used as a radiation shield – as well as being dehydrated so that any water can be recycled for drinking. "Dehydrate them as much as possible, because we need to get the water back," he said. "Those solid waste products get put into a bag, put right back against the wall."
Food too, could be used as a shield, he said. "Food is going to be stored all around the walls of the spacecraft, because food is good radiation shielding," he said. This wouldn't be dangerous as the food would merely be blocking the radiation, it wouldn't become a radioactive source.
I can see the conferences after the trip already, astronauts nervously avoiding eye contact...