Rates of obesity among children have risen sharply in many countries.

In many countries the number of children with excess weight has increased very quickly in the last twenty years. This creates serious problems, but governments, schools and families can take action.

The first problem is health. Children who are very overweight can develop diabetes, high blood pressure and problems with their joints, and doctors now see these illnesses in teenagers, although before they appeared only in older people. These children will need medical treatment for many years, and this is very expensive for the health system.

The second problem is psychological. Overweight children are often laughed at by other children at school. They lose their confidence, they do not want to do sport, and some of them become depressed or stop going to school. This can affect their whole life.

One solution is to change the food in schools. If schools sell only healthy meals and remove machines with sweets and sugary drinks, children will eat better for five days every week. Schools can also teach children how to cook simple healthy dishes.

Another solution is more physical activity. Many children spend all their free time with a telephone or a computer, so schools should give more sport lessons, and cities should build safe playgrounds and cycle paths so that children can play outside without danger from cars.

In conclusion, childhood obesity damages both the health and the confidence of children, but healthier school food and more opportunities for exercise can reduce this problem significantly.

Childhood obesity has risen sharply in many countries within a single generation. The consequences extend well beyond the individual child, and the responses that have worked are not the ones most commonly proposed.

The first and most serious problem is that childhood obesity is largely permanent. The majority of affected children remain overweight as adults, which means the condition is not a phase to be outgrown but the beginning of a lifelong trajectory. Type 2 diabetes, hypertension and joint damage are now being diagnosed in adolescents rather than in the sixties, and a person who develops diabetes at fifteen faces several decades of complications and treatment costs that health systems have not budgeted for.

The second problem is social and immediate. Overweight children experience considerably more bullying and exclusion, which affects school attendance and attainment, and often produces avoidance of exactly the physical activity that would help. The psychological damage therefore reinforces the physical condition rather than being a separate consequence of it.

The most effective solutions change the environment rather than instruct families. Taxes on sugary drinks have worked chiefly by prompting manufacturers to reformulate their products, so the sugar content of an entire market falls without any individual having to make a better choice. Restricting advertising directed at children addresses a form of persuasion that young children cannot recognise as persuasion.

Alongside this, activity has to be rebuilt into ordinary life. Children walked and cycled to school when it was safe to do so, and much of the decline in daily movement follows from roads that parents reasonably consider dangerous. Safe routes and protected play space restore activity as a default rather than as an additional weekly commitment.

In conclusion, the problems are a lifelong health trajectory and immediate social harm. Because the causes are environmental rather than individual, the effective remedies are those that change what is cheap, advertised and easy.

Childhood obesity has roughly trebled in many countries within forty years — far too quickly for anything about children themselves to have changed. What changed is the environment they grow up in, and holding that in view is what separates remedies that work from those that merely sound responsible.

The first problem is that the condition is not temporary. Obesity in childhood tracks into adulthood in the large majority of cases, so what is being established is not a current weight but a lifelong trajectory. This is why the medical picture has shifted so strikingly: type 2 diabetes, hypertension and fatty liver disease, once diseases of late middle age, are now diagnosed in adolescents. A person who becomes diabetic at fifteen faces fifty years of complications, and health systems built around treating such conditions briefly at the end of life are not structured for that.

The second problem is immediate and compounding. Affected children face substantially more bullying and social exclusion, which depresses school attendance and attainment and — crucially — produces avoidance of the physical activity that would improve matters. The social harm and the physical condition reinforce each other, which is why treating this as purely a medical issue misses how it actually progresses. Both effects follow a steep socioeconomic gradient, falling hardest on children whose families have the fewest resources to respond.

Turning to remedies, the record is instructive: decades of campaigns urging families to eat better and move more have produced very little, because they ask individuals to counteract an environment engineered against them. What has demonstrably worked is changing that environment. Levies on sugary drinks succeeded less by deterring purchases than by pushing manufacturers to reformulate, cutting sugar across whole product ranges — so the benefit reached consumers who never altered a single decision. That is the crucial property of a good intervention here: it does not require anyone to try harder.

Two further measures follow the same logic. Restricting marketing aimed at young children addresses persuasion directed at an audience that cannot recognise it as persuasion, which is a much narrower and more defensible claim than a general objection to advertising. And rebuilding activity into the ordinary day — safe walking and cycling routes, protected play space — matters because the collapse in children's movement is largely a consequence of roads parents rightly judge unsafe, not of children preferring screens. Restoring the default costs nothing in willpower.

In short, the problems are a lifelong health trajectory and a self-reinforcing social harm, both concentrated among the poorest children. Since the cause was a change in the environment, the solutions that work are the ones that change it back — and the persistent failure of advice-based approaches is the strongest available evidence for that.