It’s been a year since Chris van Tulleken set his twin brother, Xand, a challenge to help him quit his addiction to junk food. Xand had to eat an 80% ultra-processed food (UPF) diet while learning about its health impact. It worked and by the end Xand rejected all those foods he’d previously adored, including his beloved Chinese dumplings. The experiment had an aversion effect, just as Chris had hoped.

But something else happened during the experiment, Chris also had a conversion experience. A podcast about food addiction transformed into a podcast about the twins’ relationship and how best to help someone you love.

In this episode, the twins reflect on their conversion experiences – are they eating better and more importantly, are they getting on better?

Chris speaks to obesity expert Professor Rachel Batterham who tells him how the scientific discourse about UPF has developed since the end of series 1. And the twins go to see philosopher Barry Smith whose professional life has been affected by the twins’ experiment and he tells them why he’s now refusing to work with major food companies as a sensory consultant.

When Xand pops round for tea one evening, Chris’s five-year-old daughter shares some home truths about her dad and uncle’s relationship and it prompts the twins to consider what else they need to improve in their lives.

Presented by Drs Chris and Xand Van Tulleken

A Loftus Media and van Tulleken Brothers Ltd production for BBC Radio 4.

With thanks to Voltage TV for use of their archive.