Obesity is described as one of the biggest problems facing mankind. The small US territory of Puerto Rico is debating whether to fine parents who fail to get their children to lose weight. But would this work elsewhere?

More than 600 million people, or 13% of the world’s adult population, are obese. The rate more than doubled between 1980 and 2014, according to the World Health Organization. The estimated cost to the global economy is $2tn (£1.3tn), including £47bn to the UK.

National and local governments have struggled to address obesity, defined as having a body mass index – based on the ratio of height to weight – of more than 30. They often face accusations of nanny-statism and opposition from food and drink companies if they do so. Attempts have been patchy and experts are divided on what, if anything, works.

Meanwhile, families in England and several US states are sent warning letters warning if tests in schools show children are overweight.