Six Brits, who are all living with obesity, start their fact-finding global journey. They begin in Japan, a nation that has almost eradicated obesity. This has been achieved by strict government measures and a culture of shame, including fitness apps that scold the user. One of the Brits, inspired by a family tragedy, is determined to try everything, including stripping off for a Sento bath.

Six Brits, all on a personal weight-loss journey, travel to Tonga, which has one of the world’s highest rates of obesity. There they meet Ofeina who is fighting to turn around the island's obesity crisis. The group is shocked by the types of food the average Tongan eats, but a traditional diet of raw fish is not a hit. Will they manage to lose any weight by the end of the week?

The traveling Brits continue their weight-loss quest in the heart of Texas. The American food feels more familiar, but they are shocked to discover a whole industry catering to the overweight. The group are surprised to discover how hard it is to find good, cheap, fresh food in the local stores. And brewing tensions in the group finally boil over at a Texan BBQ.

Obesity is a growing problem in India, which now has 14 million obese children. The British travelers visit Mumbai, staying at the world-renowned Yoga Institute. But both the intense heat and the vegetarian diet cause them to struggle. Some embrace the teachings of the yoga masters and discover something about themselves. But will the veggie food lead to some surprises at the end-of-week weigh-in?

It’s the end of the Brits weight-loss quest around the world. They are back home in the UK and back to reality. While they managed to lose weight in every country they visited, they now face the challenge of continuing to shed the pounds. After a month apart, the group meet for a final weekend together, and one last weigh-in, to discover how they've all been doing and if they kept the weight off.