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Fat, sugar, salt - we all know we should eat less of them, and take more exercise, but as a nation with an ever expanding waistline we are becoming increasingly overweight.

Jim al-Khalili talks to Professor Susan Jebb, the UK's authority on obesity, who has spent much of her career trying to help us put those good intentions into practice.

Her challenge is not for the faint hearted. When she first got interested in obesity, as a research scientist, rates were already on the rise. Yet no one took the problem seriously. Today, with over sixty percent of adults overweight or obese, Susan remains unwavering in her commitment to ensuring we do.

As Professor of Diet and Population Health at Oxford University and Chair of the government's Responsibility Deal Food Network, she wants all of us and the food industry to improve the nation's health by translating the science of what we eat into practice.

And health is what it's all about. Obesity now poses such a danger that it's been dubbed the 'new smoking'.

Produced by Beth Eastwood.