In the final instalment of this four-part series, Jacques Peretti asks why the world's population continues to get fatter, despite the fact that billions are spent on weight loss every year. He travels to America to investigate the parallels between food companies and the tobacco industry and meets the activists battling to introduce laws to tax fatty and sugary foods - and facing fierce resistance from industry.

Jacques Peretti continues his examination of the weight-loss industry and discovers how the World Health Organisation's recognition of obesity as an epidemic provided millions of new customers for the industry. He also explores some of the latest developments in bariatric surgery and asks how far these trends will go.

In the second of this four-part series, Jacques charts the story of the fitness industry and examines the links between exercise and weight loss. He speaks to the former Global Head of Health at PepsiCo and poses the question: why does the food industry put so much money into promoting exercise? Peretti also examines some of the pharmaceutical solutions available for weight-loss, as he tells the story of the race to find a safe and effective pill to make us thin.

As obesity escalates, the diet business is booming. In this four-part series, Jacques Peretti investigates the connections between obesity and weight loss, and confronts some of the men making a fortune from our desire to become thin. Jacques examines the scientific reasons why so many diets fail long term and why - in spite of this failure - we go back to them again and again. He also speaks to a former director of Weight Watchers and meets other industry leaders, including Slimfast billionaire Danny Abrahams and Pierre Dukan, of the Dukan diet.