Chris van Tulleken is on a mission to get his twin, Xand, to quit ultra-processed food.

There’s a growing global addiction to ultra-processed food aka UPF. Chris thinks UPF is driving Xand’s (and everyone else's) weight problem. So, he proposes a simple experiment - that Xand goes on a final week-long UPF binge whilst interviewing the world's leading experts on addiction, food, nutrition and weight. It's the nutritional equivalent of smoking 100 cigarettes whilst going on a quit smoking course. Simple right? Well, it turns out to be far stranger and more emotional than either of them ever imagined...