The world may be getting richer, but the nutrition of children is getting worse. According to an analysis of over 2,400 research papers, the number of people aged 5-19 considered obese—with a body mass index (BMI) of 30 or more—increased from 11 million in 1975 to 124 million in 2016. The number of underweight children, with a BMI of less than 18.5, has also increased, from 167 million in 1975 to 192 million in 2016, although it’s fallen from a high point of 200 million in 2000.
The work, which was published on Oct. 11 in the Lancet, shows that these rates affect boys and girls differently.
Though childhood obesity increased globally over the 40 years, it did so at different rates in different parts of the world. In the South Pacific, including American Samoa, the Cook Islands, and French Polynesia, more than 30% of children were obese in 2016, compared to less than 10% in 1975. In richer countries like the US and Saudi Arabia, obesity rates increased too, but more slowly. Since the mid-2000s, they’ve leveled out around 20%, which suggests that obesity doesn’t inevitably keep rising. India, on the other hand, had the highest rates of underweight children, at about 22% for girls and 30% for boys. Other countries in southeast Asia and parts of Africa also had underweight rates of more than 10%.
As Quartz has reported before, BMI is an imperfect measure for assessing someone’s levels of body fat because it it doesn’t differentiate where fat lies (too much around organs is worse than under the skin alone), and it can’t account for the distribution of muscle (pdf), which weighs more than fat. But since it’s an easy calculation, it shows up again and again in obesity research papers.
We need fat to survive: It builds hormones, stores energy, helps us stay warm, and even cushions our vital organs. Having too much fat increases risk of problems like high blood pressure, type-2 diabetes, and high cholesterol, all of which can lead to heart disease or stroke. Too little fat in children, on the other hand, can lead to stunted mental and physical development (pdf, p. 3) and a weak immune system.
The Lancet paper warns that although globally more children are underweight than overweight at the moment, that balance can flip quickly. Countries in east Asia and middle and northern Africa saw decreases in underweight children but some of the largest rises in obesity rates.
Taken together, these patterns underline the fact that poor nutrition doesn’t just mean not getting enough calories; it can also mean getting too many, or of the wrong kind. The research team argues that somehow, policies need to ensure children get food that’s nutritious but not too rich in calories.