Prevalence And Trends Across The World

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Author(s):

	Tim Lobstein
	Dr Tim Lobstein is the Head of Policy at the World Obesity Federation.
	View Author’s Full Biography

1. Introduction

Although there are several different methods and approaches to the measurement of obesity and overweight in children, all the available surveys have one particular feature: they show a substantial and rapid increase in the numbers of children affected, in most regions of the world since the 1980s. In more developed economies child obesity prevalence levels have doubled and in some cases trebled in the period from the late 1970s to the end of the century and is highest among lower income households and some minority ethnic groups. In less developed economies child obesity levels have also risen rapidly, especially since the 1990s, and especially in urban areas and among children in better-off households .

2. Survey definitions of child overweight and obesity

For young children (under 5 years) it is common practice to use ‘weight-for-height’ rather than BMI to indicate nutritional status. The practice is based on existing definitions used to assess underweight and stunting, where a child’s weight-for-age, height-for-age and weight-for-height are compared with standard growth curves taken from a reference population.

In recent years, BMI has been used as a valid, if indirect, measure of adiposity in adults, and increasingly accepted as measure of adiposity in school-age children and adolescents for survey purposes , , and this has led to various approaches to selecting appropriate BMI cut-off values to take account of the fluctuations in BMI during normal growth. Various BMI-for-age reference charts have been developed such as those used by the US National Centre for Health Statistics, or those used by the UK Department of Health, or those developed by other national authorities. Such national reference curves provide a set of cut-offs to define overweight and obesity among children of each gender, at every age.

It should be noted that reference curves for defining overweight and obesity can help to compare different population groups and monitor changes in a population over time, but for the clinical assessment of individual children more careful examination of the child is needed to monitor individual growth trends and ensure that, for example, a high BMI is not due to extra muscle mass or to stunted linear growth.

Difficulties in making comparisons between surveys that used different national reference curves led to the establishment of an expert panel, convened by the International Obesity TaskForce (IOTF), which proposed a set of BMI cut-offs based on pooled data collected from Brazil, Britain, Hong Kong, Singapore, the Netherlands, and the USA. The panel agreed that overweight and obesity would be defined in children according to the BMI centile curves that passed through the cut-off points of BMI 25 and 30 at age 18. The resulting set of age- and gender-specific BMI cut-off points for children was published in 2000 . A more detailed version of this approach, extending the sets of cut-offs to the equivalent BMI 35 and 40, at monthly intervals from age 2 to 18 years was published in 2012 .

Although the World Health Organization (WHO) had previously recommended using a set of cut-offs based on a reference population derived from the USA, it reviewed its recommendations in 2005. The US data had included large numbers of formula-fed infants with growth patterns that differed from breast-fed infants, and this was likely to underestimate the true extent of overweight in younger children. WHO published revised standard growth charts based on data from healthy breast-fed babies and infants aged 0-5 years and extended the data statistically to provide a set of reference charts for children aged 5-19 years . These WHO standards and reference charts are discussed in more detail in the chapter in this book by De Onis. A statistical method for converting IOTF prevalence data to WHO prevalence data was published in 2023 .

As a result of these different approaches, care should be taken when looking at published prevalence figures for overweight and obesity. The prevalence levels based on one set of cut-offs or reference curves should not be compared directly with those based on another. Furthermore, the use of the cut-offs may differ, with some reports giving the prevalence value for all children experiencing overweight including those with obesity, while others may give the prevalence level for overweight excluding those categorised with obesity. Readers should also note that prevalence levels using reference curves from the USA sometimes refer to ‘at risk of overweight’ and ‘overweight’ for the top two tiers of adiposity, and sometimes to ‘overweight’ and ‘obesity’.

In addition, the survey methodology needs to be examined carefully. One of the major sources of inaccuracy is the use of self-reported or parent-reported heights and weights, instead of using direct measurements taken by professional health staff. The differences can be quite large: Figure 1 shows estimates of overweight prevalence (using WHO definitions) based on data collected by self-reported and by directly measured surveys.

Fig 1: Comparisons of self-reported and measured estimates of overweight prevalence among children aged 11 years, selected countries, 2018.

In the present chapter, unless otherwise stated the prevalence levels are based on measured weights and heights, and overweight and obesity are defined by the WHO international classification scheme.

Worldwide prevalence levels

Estimates for the global prevalence of overweight and obesity among school-age children were first made in 2004, when it was concluded that approximately 10% of school-age children (aged 5-17) were overweight, with around one quarter of these children categorised as having obesity (2% to 3% of children globally) . This global average covered a wide range of prevalence levels in different regions and countries, with the prevalence of overweight in Africa and Asia averaging well below 5% and in the Americas and Europe above 20%. More recent estimates show prevalence levels of overweight have seen a plateau or slight decline in high-income regions but rising significantly in all other regions of the world (see Figure 2).

Fig 2: Trends in the prevalence of overweight for children aged 11 in different world regions, 1990-2022

Estimated and predicted absolute numbers

The large majority of the world’s children live in less developed economies (defined by the World Bank as lower or middle income countries) and as the prevalence of overweight rises in these countries at the same time as their populations increase in size, so the absolute numbers of children with overweight has risen dramatically.

Figure 3 shows estimated and predicted prevalence of overweight and obesity globally for children and adolescents (age 5-19 years). Predictions can be modelled from existing trends, but such predictions come with a caveat: the trends will differ according to the choice of the period in the past on which the trend is modelled. As Figure 2 demonstrates, for some regions the trend has been upwards in the late part of the last century and is now showing a plateau, while in other regions the rise is very recent. In Figure 3 we have used the estimated prevalence levels for 2010 to 2020 to model possible trends through to 2040 to show what might be the case, assuming there are no interventions or disruptions that would alter the trend.

Fig 3: Trends in the global numbers of children and adolescents (aged 5-19 years) experiencing overweight or obesity

Secular trends and demographic differences

As noted already, the last three decades have seen unprecedented increases in the prevalence of child obesity. North America and some countries in Europe have and Oceania have shown early year-on-year increases in prevalence, although recent surveys indicate that the rising trends are easing, with a plateau in prevalence levels since around 2005. Other regions have shown only modest increases before the turn of the century, followed by a more rapid rise in the last two decades.

Taking the World Bank categorisation of countries by their per capita income levels, countries can be grouped as low income, lower-middle income, higher-middle income, and high income, as shown in Figure 4.

Fig 4: Trends in the prevalence of overweight among children and adolescents (aged 5-19 years) by national income category

From he projections show in Figure 4 it appears that the prevalence of overweight in upper-middle income countries will overtake the prevalence in high income countries between 2025 and 2030. For some countries the rise in overweight prevalence between 2010 and 2020 has been very dramatic: Table 1 shows the 25 countries with the most rapid rises in overweight prevalence, measured by the compound annual growth in prevalence over that decade. The rapid increase can be seen in countries in every region, and in low, lower-middle, and upper-middle income levels.

Table 1: Top twenty-five countries with the most rapid rise in prevalence levels for overweight among children and adolescents aged 5-19 years, in the period 2010-2020 

Ethnicity and gender

In the USA, obesity prevalence levels for children show consistent difference between ethnic groups in surveys across the last three decades. Overall, obesity prevalence was highest in Hispanic children (26.2%) and non-Hispanic Black children (24.8%) followed by non-Hispanic white (16.6%) and non-Hispanic Asian (9.0%) children in 2020. Among girls, obesity prevalence was highest among non-Hispanic Black girls (30.8%). Among boys, obesity prevalence was highest among Hispanic boys (29.3%). (NB ‘obesity’ is defined in the USA using local criteria.)

Similar findings are found in the UK, where Afro-Caribbean girls are more likely to be overweight than girls in the general population. Among boys, those with a South Asian background were more likely to be overweight, although there have been concerns raised about the differences in height, and in socio-economic background, making the comparisons questionable .

Socio-economic factors

As shown above, the national income levels show a marked effect on the trends in overweight prevalence. Within countries there is a more complex relationship between household income and the likelihood of children experiencing overweight or obesity. In countries which are not economically developed, or are undergoing economic development, overweight and obesity levels tend to be higher among families with larger incomes or higher educational attainment. For example, in Brazil, in 2005, 38% of 11-year-old children in higher-income families had overweight or obesity (WHO definition), compared with 26% of children in middle-income families and 20% of children in lower income families . In China there is a similar association between child overweight and family income level and educational level . In a review across many developing countries, the determinants of risk of obesity in these countries were found to be: “high socioeconomic status, residence in metropolitan cities, female gender, unawareness and false beliefs about nutrition, marketing by transnational food companies, increasing academic stress, and poor facilities for physical activity” .

In high income countries the reverse tends to be the case, with children in lower income households more likely to experience overweight or obesity. In the USA, obesity prevalence among children in families where the head of household did not gain a high school diploma are two- to three-times the prevalence among families where the head of household has a university degree . A review of European studies found the likelihood of children experiencing obesity was higher in households with lower parental education, lower parental occupation status, lower parental income and in some countries poorer neighbourhood deprivation scores . Secular trends show that in several European countries these social class differences in the likelihood of obesity appear to be widening .

The relationship between child overweight and socio-economic status has a further nuance in developed economies at the country level. Those countries with a higher level of social inequality (measured by size of the difference between the lowest and highest households in terms of income or deprivation) also show a higher level of child obesity, independent of the level of average wealth measured by Growth Domestic Product (GDP) . The greater the inequity in a country, the greater the prevalence of obesity. For policy-makers, reducing the relative social deprivation across society as a whole may improve the effectiveness of policies to tackle obesity and promote healthy child growth.

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Table 1: Top twenty-five countries with the most rapid rise in prevalence levels for overweight among children and adolescents aged 5-19 years, in the period 2010-2020 

CAGR = Compound annualised growth rate

Source: World Health Organization Global Health Observatory , World Obesity Federation , and World Bank

Fig 1: Comparisons of self-reported and measured estimates of overweight prevalence among children aged 11 years, selected countries, 2018.

Overweight defined by WHO criteria (includes obesity).

Sources:

Self-reported data for 2018 from Health Behaviour of School-Aged Children

Measured data for 2018 estimated by the NCD Risk Factor Collaboration

Fig 2: Trends in the prevalence of overweight for children aged 11 in different world regions, 1990-2022

Overweight including obesity, defined by WHO criteria

Source: NCD Risk Factor Collaboration 2024 (https://ncdrisc.org)

Fig 3: Trends in the global numbers and prevalence of children and adolescents (aged 5-19 years) experiencing overweight

Overweight including obesity, defined by WHO criteria

Source World Health Organization Global Health Observatory , and World Obesity Federation .

Fig 4: Trends in the prevalence of overweight among children and adolescents (aged 5-19 years) by national income category

Overweight including obesity, defined by WHO criteria

Income category defined by World Bank

Source World Health Organization Global Health Observatory , World Obesity Federation , and World Bank .