A boy struggles while doing a sit-up at a summer camp to tackle child obesity in Zhengzhou, Henan province, on July 14, 2013. [Photo by Zhang Tao/Asianewsphoto]

Today, more than 2.1 billion people - nearly 30 percent of the global population - are overweight or obese. That is nearly two and a half times the number of adults and children who are undernourished. Obesity is responsible for about 5 percent of deaths worldwide.

This crisis is not just a pressing health concern; it is also a threat to the global economy. The total economic impact of obesity is about $2 trillion a year, or 2.8 percent of world GDP - roughly equivalent to the economic damage caused by smoking or armed violence, war and terrorism, according to a new research by McKinsey Global Institute.

And the problem is likely to worsen. If the current trend continues, almost half of the world's adult population will be overweight or obese by 2030.

This global epidemic is not confined to advanced countries. As emerging economies climb out of poverty, people there are becoming fatter. More than 60 percent of the world's obese people live in developing countries, where rapid industrialization and urbanization are boosting incomes and therefore calorie intake. In India and China, the prevalence of obesity in cities is 3-4 times the rate in rural areas.

Indeed, the evidence suggests that developing countries are especially vulnerable to the epidemic. Obesity rates tend to explode in countries where food was once scarce and suddenly became plentiful.

To make matters worse, in countries with limited public healthcare services, the cost of healthcare falls directly on the afflicted households. As a result, obesity can lock in poverty and perpetuate inequality.

Through a review of 500 intervention trials around the world, MGI has identified 74 potential interventions that could be used to address obesity. These include subsidized school meals, urban design that encourages walking, better nutritional labeling, restrictions on the advertising of high calorie food and drinks, and fiscal measures.