The past 40 years have seen an unprecedented increase in the number of obese adults worldwide, climbing to about 640 million from 105 million in 1975. If the current trend continues, about one-fifth of adults will be obese by 2025.
The rate has more than doubled for women and tripled for men, according to a new analysis published in the Lancet. Under the present trajectory, the chance of meeting a goal set by the World Health Organization to halt the increase over the next decade is, according to the study, "virtually zero."
Behind the global spike is greater access to cheap food as incomes have risen. "It's been very easy, as countries get out of poverty, to eat a lot, and to eat a lot of unhealthy calories," said Majid Ezzati, the study's senior author and chair of global environmental health at Imperial College London. The price of fresh fruits, vegetables, and whole grains are often "noticeably more than highly processed carbohydrates," he said.
A person who has a body-mass index higher than 30, or weighs at least 203 pounds and is 5 feet 9 inches tall, is considered obese. The world population's average weight has increased by about 3.3 pounds (1.5 kilograms) per decade since 1975, the researchers estimate. Excess weight raises the risk of diabetes, heart disease, and other chronic conditions.
Governments need to prepare for the jump in medical costs that accompany unhealthy weight and focus on prevention now to avoid higher costs in the future, said Bill Dietz, director of the Sumner M. Redstone Global Center for Prevention and Wellness at George Washington University.
"They should be as nervous as a cat on a hot tin roof about the tsunami of diabetes that's coming their way," Dietz said. "The cost of this rise in the prevalence of obesity is going to be staggering."
Working under the banner of the Non-Communicable Disease Risk Factor Collaboration, Ezzati and hundreds of colleagues from around the world gathered data from surveys that measured the height and weight of 19 million adults. They then used statistical methods to estimate trends in global and national weight patterns from 1975 to 2014.
The main takeaway? Excess weight has become a far bigger global health problem than weighing too little. While low body weight is still a substantial health risk for parts of Africa and South Asia, being too heavy is a much more common hazard around the globe.
For women, this transformation took place many years ago. Obese women have outnumbered those who are underweight for more than a decade, according to the Lancet analysis. For men, being underweight was still a bigger problem until about 2011. Adults are considered underweight if their BMI is below 18.5, or weighing less than 125 pounds for someone 5 feet 9 inches. In 1975, more than twice as many people were underweight than obese.
Ezzati said the trends are related. "The issue really comes down to people either not having enough to eat or not having enough healthy food to eat," he said. "It becomes a manifestation of the same problem."
No government has found a way to stop rising obesity, though some are trying. Mexico, with almost two-thirds of its population overweight or obese, enacted a national tax on sugary beverages in 2014, the first large country to do so. An early evaluation suggests the peso-per-liter levy steered soda sales lower. Ezzati said the world also needs to focus on making more healthy foods competitive with cheap, processed foods. "To me, how to change the price of good things is perhaps the bigger question going forward," he said.
The Lancet analysis also estimates an alarming rise of extreme cases of obesity. The global rate of severe obesity, or BMI over 35, is on pace to surpass 9 percent in women and 6 percent in men by 2025. That category now includes 39 million adults in the U.S. In 1975, it was 4 million.
Meeting the WHO target of halting the rise in obesity by 2025 "will require action of monumental proportions," Boyd Swinburn, a professor of population nutrition and global health at the University of Auckland in New Zealand, said in an e-mail. The goal "is likely to be impossible" for adults but may be feasible for children in some countries, he said. The increase in obesity has been steeper in low- and middle-income countries compared with wealthier ones "where the epidemic started early and rose more slowly," Swinburn said.
The rich world can blunt the health impacts of unhealthy weight with drugs to help control diabetes, harmful cholesterol, high blood pressure, and other health consequences. Health systems in the developing world may not be equipped to do the same. "Are they prepared to deal with downstream effects as we enter this situation of severe obesity?" Ezzati said.