World hunger has fallen. Now what do we do about the planet’s expanding waistline?

Scroll forward to today, and this emerging superpower symbolises the amazing pace of global change. The streets of its booming cities are filled with cars rather than bicycles, while teenagers throng fast-food restaurants, parents spoil their only children with sweet treats and meat consumption soars. And in the slipstream of progress comes the curse of modern life: obesity.

Close to one-third of Chinese people are overweight, their numbers almost doubling in three decades. In some cities, 20 per cent of residents are obese, the incidence rising fast among schoolchildren. Alongside expanding waistlines and rapidly changing diet come a host of attendant health problems; half the country’s population is thought to be pre-diabetic, for example, with one in nine having the full-blown condition.

This week the obesity epidemic led doctors and academics to declare war on sugar in Britain, declaring it is as deadly as tobacco. A new campaign highlighted how dangers do not just lurk in those enticing fizzy drinks with the equivalent of nine lumps of sugar in one can; even low-fat yogurts and ‘healthy’ soups contain hidden sugars.

It was a deliberately alarmist message. Yet sugar is not intrinsically harmful, unlike the daft habit of filling your lungs with tobacco smoke – the core problem is over-consumption of calories combined with too little exercise. They were right to press the panic button, however, not least since health care costs for obese people are substantially higher than for slimmer citizens at a time when budgets are under intense pressures.

But we need to realise that obesity is a global issue – and the biggest concerns are now in the developing world. Days before the experts’ call to arms against sugar, a powerful report from the Overseas Development Institute (ODI) highlighted the scale of the problem. More than one-third of the world’s adults are too heavy – and counter-intuitively almost twice as many overweight people are found in poor countries as in rich ones.

Over almost three decades, the number of obese or overweight people in developing nations rose from 250 million to 904 million. This means more people in poorer countries go to bed each night having consumed too many calories than go to bed hungry, an incredible change and a sign of how much-maligned capitalism is changing the world at such breathtaking speed. Their obesity rates are rising far faster than in wealthier nations.

The title of world’s fattest nation is no longer held by the United States but Mexico, where fast-food joints have proliferated, more Coca-Cola is drunk than in its homeland and two-thirds of people are overweight. Rates in Latin America and the Middle East match those in Europe, while rising rapidly across much of sub-Saharan Africa. The problem is bigger in South Africa, for all its poverty, than in Britain, among the worst European offenders.

All this wobbly flesh is a weird sign of success; why else would KFC be spreading its wings so rapidly across Africa? Despite Malthusian predictions of doom, it serves as a reminder of humankind’s astonishing ability to feed soaring populations. Cereal yields in developing countries have increased this century at twice the rate of population growth, while the amount of fruit harvested per head doubled in half a century.

Almost one billion people have been lifted from extreme poverty in two decades – and body mass index rises alongside economic growth. People eat more and have richer diets, while walking and cycling less as they shift from working in rural fields to sitting in urban offices. More women have jobs, which leads to less home cooking and healthy eating; one study found a 10 per cent increase in female workers leads to a 70 calorie rise in average daily consumption.

A small net increase in calories can lead to big rises in obesity. And all those plump bellies prompt new challenges, from controlling food firms and farming lobbies to rethinking urban planning and putting fresh pressures on struggling health services. Obesity has grown faster than any other cause of disease. The consumption of too much food, too much salt and too much fat at a time of lengthening life expectancy leads to more cancer, heart disease and strokes as well as diabetes.

We should not downplay the grinding hunger that still scars the globe. More than 800 million impoverished people have too little food and one third of infants in the developing world are stunted. There is also evidence that underfed babies gain weight more easily, especially when switching diets, making obesity a tougher problem to crack in developing countries. Healthy food costs more too; in South Africa, the ODI researchers found it two-thirds more expensive than a typical diet.

But forget those old aid industry stereotypes of starving Africans in need of our supposed salvation. Core issues today are equality and governance. Three-quarters of the world’s poorest people live in middle-income countries. Fast-rising China is home to more of the ultra-rich than anywhere apart from the US – alongside one in seven of the planet’s poor. And champagne sales boom in Nigeria while we hand over huge sums in aid.

After centuries fighting starvation, the planet’s population is now confronted by a profound new problem. ‘We’ve made real progress working out how to ensure people have enough to eat,’ said Steve Wiggins, author of the ODI report. ‘But we don’t know enough about how to deal with people eating too much of the wrong foods. It’s the new challenge of our times.’