Recently，childhood obesity has become the greatest cause for concern.For children in year six obesity rates have increased at a significant pace—around 5% a year for the past decade—so that now one in three children are obese by the time they leave primary school.The rate of childhood mental illness is accelerating and is both a cause and a symptom of the obesity crisis.
Obesity is one of the most complex public health challenges that we face.It does not have a single cause.The reasons for it are wide-ranging.But above all，it is a social challenge.It is about education and social norms for eating and exercise.It is about how food companies formulate their products，how they are labelled and advertised，and how they are priced and displayed in shops.Work and school play a crucial role：more and more jobs are sedentary (久坐的) and lads are less and less likely to expend energy playing outdoors.The quality of our public spaces and transport systems makes an important difference too.
We argue for fresh thinking to challenge the assumption that issues like obesity are a " disease of the will" and to encourage more support for people to make healthier choices.Local authorities should be given new powers to stop fast-food outlets opening near schools，to prevent them from selling high-calorie products to schoolchildren，and to ban junk food advertising near the school gates.
We must remember that unhealthy behaviour today is costly tomorrow.Now is the time for more action and more investment—the quality and length of our children's lives depend on it.
What does the author say about the cause of obesity?无