Dr Chris Smith and the Naked Scientist team present the latest science news, analysis and breakthroughs, In this week's episode we discuss why our belly fat could be key to helping people with spinal injuries, a breakthrough in understanding why the BRCA genes lead to breast cancer in some people and we look at the new breed of synthetic opioids making their way on to the streets of Britain, and find out why they’re so deadly. Get the podcast from the BBC Sounds app.