That's good news for the U.S., and it should come as a relief to the developing world. Across Asia, Africa, and Latin America, countries are in the first stage of the nutrition transition, away from widespread malnourishment. Almost as rapidly, they are entering a second stage: toward a spiraling body mass. The evidence that this trend can be halted and reversed provides hope that the whole world can achieve a Goldilocks equilibrium: none hungry and few burdened by obesity.
One of the greatest signs of progress in the developing world over the past 50 years has been the decline of famine and malnourishment. In the early 1990s, stunting -- being considerably shorter than average because of a lack of nutrition -- affected around 20 percent of children in Brazil, 30 percent in China and 55 percent in Pakistan. That has dropped below 10 percent in both Brazil and China and to 43 percent in Pakistan.
1.5 Billion Overweight or Obese Adults
While malnutrition is on the decline, average weights are rising. Global obesity rates have doubled since 1980, and nearly 1.5 billion adults worldwide are either overweight or obese. In China, more than 10 percent of the population is obese. By 2010, 35 million children in developing countries were estimated to be overweight and obese, compared with 8 million children in wealthy countries.
In the U.S. and Europe, serious malnutrition largely died out decades before the epidemic of obesity began. In many developing countries, the two have overlapped. In 2010, 8.5 percent of African children were overweight or obese. That's above the global average of 6.7 percent. But the Food & Agriculture Organization also suggests one in four in the region are still malnourished. Within the same family, children show signs of malnourishment even as siblings or parents packed on the pounds. In some countries as many as two-thirds of households with an underweight member also contain an overweight person.
Less Disease + Better Jobs = Weight Gain
Largely positive trends -- improved public health combined with rapid growth and greater access to cheap calories -- are behind the increase in global body mass. Over time, children in particular have become less exposed to infectious disease, and they lose less of what they consume to diarrhea and other intestinal illnesses. As a result, the same amount of food leads to more nutrition. Meanwhile, even economically stagnant countries have seen a move toward less-backbreaking forms of work. People are leaving the fields to work in shops and offices. Rather than carrying water from a local well, they get it straight from the faucet. In addition, as people get richer, they eat more. They also eat differently, consuming more meats and fats.
The trends of urbanization, improved health and increased wealth look set to continue worldwide. Hopefully the scourge of malnutrition will soon die out as a result, with every country completing the first stage of the nutrition transition. The good news about declining child obesity in the U.S. is that it suggests an endpoint to the transition other than universal obesity, diabetes, hypertension and decreased mobility. It provides hope that a growing proportion of the planet's population could suffer from neither lack nor excess. In the U.S., it's plausible that new rules on federal nutrition assistance as well as public health campaigns played a role in improving the quality of children's diets and reduced obesity risk factors, such as smoking during pregnancy. If these gains can be consolidated, expanded and spread to the rest of the world, perhaps a combination of development, healthy diet and exercise can fend off diseases of the poor and rich alike.
Charles Kenny is a senior fellow at the Center for Global Development and author of "The Upside of Down: Why the Rise of the Rest is Great for the West."