Don't blame fast food, television or the car - fat is a technological issue: "We've long blamed television for turning us into a nation of couch potatoes but now the dismal science is weighing in with the idea that it is technology, rather than a change in tastes or the growth of fast food restaurants, that is the cause of obesity.

Professor Carol Propper, of Bristol University, says economics can bring valuable insights into the world of over-eating and says technology has both reduced the cost of food as well as making work and life less strenuous."