Over the past 40 years the world’s population has gotten about 1.5 kilograms heavier each year, leading to an obesity epidemic. According to a study published in The Lancet, there are now roughly 640 million obese individuals around the world. The study found that not only is the number of obese people greater than ever before but that it has surpassed the number of those dangerously underweight as well. The study looked at trends in adult body mass index, which quantifies an individual’s tissue mass based on height and weight, across 200 countries between 1975 and 2014. As the following graphic shows, the U.S. in particular saw a dramatic increase from 1.6 to 13.3 percent of the population being morbidly obese whereas the portion that was underweight dwindled from 7 to 2.5 percent.

Researchers have been trying to track down what causes obesity, looking at potential triggers such as artificial sweeteners and the almost inescapable prevalence of food for sale. The implications of obesity have also been a topic of interest, including studies of a potential link to autism for children born to diabetic and obese mothers and other research that indicates obesity as a possible risk factor for cognitive decline. Some of the best opportunities to combat childhood obesity take place in school: Increased physical activity and healthier school lunches make a big impact, but both are rare in the U.S., which shares with China the world’s highest obesity rates.

Source: "Trends in adult body-mass index in 200 countries from 1975 to 2014: a pooled analysis of 1698 population-based measurement studies with 19.2 million participants," by NCD Risk Factor Collaboration (NCD-RisC) in The Lancet, Vol. 387, April 2, 2016.
Graphic by Amanda Montañez