Analysis of 3663 population-based studies showed a global transition from underweight dominance to obesity dominance over the past 3 decades. This transition was already apparent in adults in 1990 and by 2022, also in children and adolescents.

This summary is based on the publication of NCD Risk Factor Collaboration (NCD-RisC) - Worldwide trends in underweight and obesity from 1990 to 2022: a pooled analysis of 3663 population-representative studies with 222 million children, adolescents, and adults. Lancet. 2024 Feb 29:S0140-6736(23)02750-2 [Online ahead of print]. doi: 10.1016/S0140-6736(23)02750-2

Underweight and obesity: two sides of the same coin

Since the 1990s, obesity is being viewed as an epidemic, in a similar way as undernutrition is. As underweight and obesity are associated with adverse health outcomes throughout life, optimal nutrition and health policies should target both these forms of malnutrition [1]. Global data on the combined (double) burden of underweight and obesity, however, are scarce. The NCD Risk Factor Collaboration therefore sought to estimate the worldwide individual and combined prevalences of underweight and obesity, and their changes, among adults, children, and adolescents in 200 countries and territories from 1990 to 2022. The researchers collected data from 3663 population-based studies (222 million participants in total) in which height and weight were measured in representative samples of the general population. Pooled data were analyzed using a Bayesian hierarchical meta-regression model to estimate trends in the prevalence of (1) underweight in adults (age ≥20 years; BMI <18.5 kg/m²) or thinness in school-aged children and adolescents (age 5–19 years; BMI <2 SD below median of WHO growth reference) and (2) obesity (adults: BMI ≥30 kg/m²; children/adolescents: BMI >2 SD above this median). The prevalence of double burden was calculated as the sum of the prevalences of underweight or thinness and obesity.

Trends in adults

In adults, the global age-standardized prevalence of underweight decreased from 14.5% (95% credible interval (CrI; representing 2.5th–97.5th percentiles of posterior distributions): 14.0%–15.0%) in 1990 to 7.0% (95%CrI: 6.5%–7.5%) in 2022 in women and from 13.7% (95%CrI: 13.0%–14.4%) to 6.2% (95%CrI: 5.6%–6.9%) in men. During the same period, the global age-standardized prevalence of obesity increased from 8.8% (95%CrI: 8.5%–9.1%) to 18.5% (95%CrI: 17.9%–19.1%) in women and from 4.8% (95%CrI: 4.6%–5.0%) to 14.0% (95%CrI: 13.4%–14.6%) in men. From 1990 to 2022, the combined prevalence of underweight and obesity decreased in 11 countries for women and 17 countries for men, with a posterior probability ≥0.80 that the estimated changes were true changes. During the same period, the combined prevalence increased in 162 countries for women and 140 countries for men. In 2022, the combined prevalence was highest in island nations in Polynesia and Micronesia and the Caribbean and countries in the Middle East and North Africa. In almost all countries, the decrease in the combined prevalence was driven by a decrease in underweight, whereas the increase in double burden was caused by an increase in obesity. In 1990, underweight was more prevalent than obesity (posterior probability ≥0.80) in 65 countries for women and 89 countries for men. By 2022, fewer countries had a higher prevalence of underweight than obesity (posterior probability ≥0.80), namely 16 for women and 39 for men. In contrast, the number of countries where the prevalence of obesity was higher than that of underweight (posterior probability ≥0.80) increased from 128 to 177 for women and from 104 to 145 for men.

Trends in children and adolescents

From 1990 to 2022, the global age-standardized prevalence of thinness in school-aged children and adolescents decreased from 10.3% (95%CrI: 9.5%–11.1%) to 8.2% (95%CrI: 7.3%–9.0%) in girls and from 16.7% (95%CrI: 15.6%–17.8%) to 10.8% (95%CrI: 9.7%–11.9%) in boys (posterior probability >0.999). The global age-standardized prevalence of obesity increased from 1.7% (95%CrI: 1.5%–2.0%) in 1990 to 6.9% (95%CrI: 6.3%–7.6%) in 2022 in girls and from 2.1% (95%CrI: 1.9%–2.3%) to 9.3% (95%CrI: 8.5%–10.2%) in boys (posterior probability >0.999). Over the 3 decades, the combined prevalence of thinness and obesity (posterior probability ≥0.80) decreased among girls in 5 countries and boys in 15 countries, whereas it increased among girls in 140 countries and boys in 137 countries. The countries with the highest combined prevalence of thinness and obesity in 2022 were located in Polynesia and Micronesia and the Caribbean for both sexes (plus Chile and Qatar for boys only). The combined prevalence was also high in several countries in South Asia, such as Sri Lanka and India , but thinness remained prevalent here despite having declined. Similar to adults, the decreases in the combined prevalence were mostly driven by declining thinness and the increases in double burden were generally due to increasing obesity. In 1990, 93 countries had a higher prevalence of thinness than obesity (posterior probability ≥0.80) for both girls and boys, which decreased to 35 and 42 countries, respectively, in 2022. Conversely, the prevalence of obesity was higher than that of thinness (posterior probability ≥0.80) in 52 countries (girls) and 47 countries (boys) in 1990 and in 133 countries (girls) and 125 countries (boys) in 2022.

Need for a healthy nutrition transition

From 1990 to 2022, the prevalence of malnutrition (i.e., underweight/thinness plus obesity) increased in most countries, except for most countries in South Asia and some in Southeast Asia and sub-Saharan Africa. Specifically, many countries experienced a transition from underweight dominance to obesity dominance. The authors point that this transition was already apparent in adults in 1990 in a large part of the world, and by 2022, the obesity dominance was also visible in school-aged children and adolescents. Several low-income and middle-income countries now have a higher obesity prevalence than industrialized high-income countries. While major changes in food policies and programs and nutrition took place over the past 3 decades, the authors conclude “[t]here is a need throughout the world for social and agricultural policies and food programs that address the remaining burden of underweight while curbing and reversing the rise in obesity by enhancing access to healthy and nutritious foods.”

Find this article online at Lancet.

References

1. United Nations. Sustainable Development Goal Target 2.2. In: The Sustainable Development Goals Report 2023: Special Edition. New York: United Nations Publications; 2023. Accessed March 5, 2024. https://unstats.un.org/sdgs/report/2023/The-Sustainable-Development-Goals-Report-2023.pdf