To estimate the overall prevalence and absolute burden of overweight and obesity in the world and in various regions in 2005 and to project the global burden in 2030.
We identified sex- and age-specific prevalence of overweight and obesity in representative population samples from 106 countries, which cover approximately 88% of the world population, using MEDLINE and other computerized databases, supplemented by a manual search of references from retrieved articles.
Sex- and age-specific prevalence of overweight and obesity were applied to the 2005 population to estimate the numbers of overweight and obese individuals in each country, each world region and the entire world. In addition, the prevalence, with and without adjusting for secular trends, were applied to the 2030 population projections to forecast the number of overweight and obese individuals in 2030.
Overall, 23.2% (95% confidence interval 22.8–23.5%) of the world's adult population in 2005 was overweight (24.0% in men (23.4–24.5%) and 22.4% in women (21.9–22.9%)), and 9.8% (9.6–10.0%) was obese (7.7% in men (7.4–7.9%) and 11.9% in women (11.6–12.2%)). The estimated total numbers of overweight and obese adults in 2005 were 937 million (922–951 million) and 396 million (388–405 million), respectively. By 2030, the respective number of overweight and obese adults was projected to be 1.35 billion and 573 million individuals without adjusting for secular trends. If recent secular trends continue unabated, the absolute numbers were projected to total 2.16 billion overweight and 1.12 billion obese individuals.
Overweight and obesity are important clinical and public health burdens worldwide. National programs for the prevention and treatment of overweight, obesity and related comorbidities and mortalities should be a public health priority.
The prevalence of overweight and obesity is increasing at an alarming rate in developed and developing countries throughout the world.1, 2 Epidemiologic studies indicate that overweight and obesity are important risk factors for diabetes, cardiovascular disease, cancer and premature death.2 The high prevalence of overweight and obesity, combined with their concomitant health risks, makes it a particularly relevant worldwide public health challenge.
The prevalence of overweight and obesity has been reported from individual countries in various regions of the world. However, these data have not been systematically reviewed and pooled to estimate the worldwide prevalence and absolute burden of overweight and obesity. Given the increasing public health importance of overweight and obesity in economically developed and developing countries, accurate estimates of the global burden of this condition are critical to the development of public health strategies for its primary prevention and treatment. We analyzed data from population-based studies in different world regions to estimate the overall prevalence and absolute burden of overweight and obesity in the world and various regions in 2005 and to project the global burden in 2030.
Materials and methods
A literature search of the MEDLINE database using the medical subject headings body mass index, body weight, obesity, prevalence, and cross-sectional studies and the key word overweight was conducted. The search was restricted to studies in humans published from January 1990 through August 2007. A manual search was performed using references cited in relevant review and original study articles. In addition, we searched international statistical agency websites provided by links from the US census bureau, as well as the World Health Organization's (WHO) Global Cardiovascular and Noncommunicable Disease Infobases.3, 4, 5 Eligibility criteria for inclusion were (1) population-based cross-sectional survey published in a peer-reviewed journal or by a government agency from 1990 onward in which the prevalence of overweight and/or obesity was reported; (2) body height and weight were measured; (3) overweight and obesity were defined as a body mass index (BMI) of 25–29.9 and ⩾30 kg/m2, respectively; and (4) age- and gender-specific prevalence of overweight and/or obesity were provided. If national data were available for a country, the most recent data were used. Otherwise, data from multi-site or regional studies were used. If data from more than one region of a country were available, all available data were utilized. Overall, 72 national, 22 multi-site, and 14 regional studies from 106 countries, covering approximately 88% of the world population, were included in the analysis (references provided in online supplementary data, references 1–97). Study characteristics, mean BMI, and the crude prevalence of overweight and obesity from each study are shown in the online data Supplementary Table 1. All data were extracted independently by two investigators using a standardized protocol and data collection form.
Countries were grouped together into world regions according to the World Bank's World Development Report 1993,6 and included: the established market economies (EME), mainly consisting of high-income members of the Organisation for Economic Cooperation and Development; the former socialist economies of Europe (FSE); Latin America and the Caribbean (LAC); China (CHN); India (IND); the middle eastern crescent (MEC), which includes North Africa, the Middle East, Pakistan, and the Central Asia Republics of the former Soviet Union; other Asia and Islands (OAI) which covers the rest of Asia and the Pacific; and sub-Saharan Africa (SSA). The criteria used by the World Bank to define these regions include the level of socioeconomic development, epidemiologic homogeneity, and geographic proximity.6
For countries without valid estimates of prevalence, we applied data from the country within the same world region with the most similar gross national income per capita (GNI) or, if GNI was not available for the country, we applied data from the country with the closest geographic proximity (online data Supplementary Table 2). In addition, not all studies provided data for the full age range under consideration. Missing age ranges for these studies were estimated by applying data from the country with the most similar GNI within the same world region. GNI was chosen as an indicator of overweight and obesity risk among countries because it is the method used to classify world regions and previous studies have reported an association between GNI and prevalence of overweight and obesity.7
For several countries (Switzerland, Bulgaria, Poland, Russia, India, Sri Lanka, Vietnam, Gambia, Madagascar and Tanzania), prevalence data were available from multiple regional studies but not national studies. In these countries, the regional studies were combined, weighted by the proportion of the population in each region of the country to provide the estimates of prevalence of overweight and obesity for the country. For India, the rural study did not include the oldest or youngest age groups. Data from the urban Indian study was used to estimate the prevalence in these age groups after adjusting for urban/rural difference in the prevalence. Similarly, the most recent national data for China did not include prevalence estimates for the 20 to 29-year age group. The 1991 national data were used to estimate the prevalence of overweight and obesity in this age group after adjusting for period difference in the prevalence.
Some studies did not provide age-specific data in the 10-year increments presented in this analysis (that is, 20–29, 30–39, and so on). We used a population-weighted average of the prevalence from the two closest 10-year age groups (for example, mean of the prevalence in the 15 to 24 and 25 to 34-year age groups for the 20 to 29-year age group) to estimate the prevalence of overweight and obesity for the age ranges under consideration here.
The prevalence of overweight and obesity within countries was standardized by age to the 2005 world population8 separately for each sex and overall using the direct method. Sex- and age-specific prevalence of overweight and obesity were applied to the WHO sex- and age-specific population count in 2005 to estimate the numbers of overweight and obese people in the country for each sex and age group. The total numbers of overweight and obese persons in each country were estimated separately for men and women. The total numbers of overweight and obese persons in each country were summed to provide an estimate of the total numbers of overweight and obese individuals for each region, and the numbers from each region were added to obtain worldwide counts. The prevalence of overweight and obesity for 2005 was calculated by dividing the total number of overweight and obese persons within each region by the total number of residents in that region. We estimated the worldwide prevalence by dividing the total number of overweight and obese persons by the total adult world population. Standard errors for the prevalence of overweight and obesity were taken from those studies that reported them. For the remaining studies, s.e. were estimated as the square root of ((prevalence of overweight or obesity × (1-prevalence of overweight or obesity))/sample size in the survey), which may slightly overestimate the s.e. for surveys utilizing complex sampling designs. The s.e. for the numbers of overweight and obese persons within a region and worldwide were then estimated with Taylor series approximation methods.9 These calculations were used to provide 95% confidence intervals.
Two methods were used to forecast the absolute numbers of overweight and obese persons in 2030 under different assumptions. First, we assumed that the prevalence of overweight and obesity would be constant in the future. The projections are based on current prevalence of overweight and obesity, population growth and demographic changes including age composition of the population and urbanization for regions that provided data for both urban and rural areas (China, India, other Asia and Islands and sub-Saharan Africa). Second, we assume a secular trend in the increase of overweight and obesity will continue based on data from selected countries within each region (references provided in online supplementary data, references 16, 100–124). The projections are based on the most recent regional secular trends in prevalence of overweight or obesity estimated from available data, population growth and demographic shifts (age distribution and urbanization). These regional projections were summed and used to provide estimates of the global burden and prevalence of overweight and obesity in 2030.
Figure 1 shows the estimated age-standardized prevalence of overweight (upper) and obesity (lower) in 2005 among adults 20 years and older for all countries in the world. The age-standardized prevalence of overweight and obesity by gender and overall for each country with available data is shown in the online data Supplementary Table 3.
Figure 2 (upper) illustrates the estimated age-standardized prevalence of overweight and obesity in people aged 20 years and older for 2005 by world regions. Overall, 23.2% (95% confidence interval (CI) 22.8–23.5%) of the world's adult population was overweight (24.0% of men (23.4–24.5%) and 22.4% of women (21.9–22.9%)), and 9.8% (95% CI 9.6–10.0%) of the world's adult population was obese (7.7% of men (7.4–7.9%) and 11.9% of women (11.6–12.2%)). For both men and women, the highest estimated prevalence of overweight and obesity combined was in the established market economies and the lowest estimated prevalence of overweight and obesity combined was in India. The prevalence of obesity was consistently higher among women compared with men in all world regions. However, the relation between overweight and gender varied by world regions (Figure 2). Within each region, gender differences in overweight and obesity were generally consistent across all age groups (Table 1). In addition, obesity prevalence tended to increase with age until peaking in the middle-age group and decreased thereafter. There was no consistent relationship between overweight prevalence and age.
Figure 2 (lower) shows the estimated absolute numbers of overweight and obese adults aged 20 years and older in different world regions in 2005. The estimated total number of overweight persons was 937 million (95% CI 922–951 million), and an additional 396 million (388–405 million) persons were estimated to be obese. An estimated 326 million (320–331 million) overweight persons and 188 million (183–193 million) obese persons lived in economically developed countries, whereas 611 million (597–625 million) overweight persons and 209 million (202–215 million) obese persons lived in economically developing countries. The region with the greatest estimated number of overweight and obese persons was the established market economies.
Projections of the absolute burden and prevalence of overweight and obesity in 2030 are given in Table 2. The more conservative projection, which only considered changes in population and urbanization but not secular trends in prevalence, indicates that the numbers of overweight and obese individuals will increase by 44 and 45%, respectively, from 2005 estimates, totalling to 1.35 billion overweight and 573 million obese individuals in 2030. If recent secular trends continue unabated, the absolute numbers could rise to a total of 2.16 billion overweight and 1.12 billion obese individuals, or 38 and 20% of the world's adult population, respectively. The numbers of overweight and obese individuals are expected to increase most rapidly in developing regions of the world, and depending on future trends, these estimates may range from increases of 62–205 and 71–263% in the numbers of overweight and obese persons, respectively. All projections indicate that China will exceed the established market economies in the total number of overweight men and women by 2030.
We conducted a sensitivity analysis by only using data from peer-reviewed publications. Overall, 22.5% (95% CI 22.1–22.9%) of the world's adult population in 2005 was overweight (23.2% in men (22.7–23.7%) and 21.8% in women (21.3–22.3%)), and 9.7% (95% CI 9.5–9.9%) of the world's adult population was obese (7.5% in men (7.3–7.8%) and 11.8% in women (11.5–12.1%)).
Our analysis indicates that overweight and obesity are significant and increasing public health challenges in both economically developed and developing regions of the world, with 33.0% of the world's adult population (1.3 billion people) overweight or obese in 2005. Moreover, if recent trends continue, by 2030 up to 57.8% of the world's adult population (3.3 billion people) could be either overweight or obese.
The prevalence of overweight and obesity was higher in economically developed countries compared with economically developing countries, 35.2 vs 19.6% and 20.3 vs 6.7%, respectively, in 2005. Although overweight and obesity is more common in economically developed countries, the much larger population of developing countries results in a considerably larger absolute number of individuals affected. Moreover, compared with developed regions of the world, developing regions are projected to have a much larger proportional increase in the number of overweight and obese individuals between 2005 and 2030. Growth in population size, population aging, urbanization and changes in lifestyle including increases in total calorie intake and reductions in physical activity, all contribute to an epidemic of overweight and obesity in developing regions.
Obesity prevalence peaks in the 60 to 69-year age group for both men and women in economically developed regions and in even younger age in developing regions. This might reflect a survival bias or weight loss in older age because of increased chronic diseases.
The estimates in our analysis are limited by several factors. Prevalence data were not available for 115 countries. For these countries, prevalence of overweight and obesity were estimated using the prevalence from the country with the most similar GNI or closest geographic proximity within the same world region. Although some misestimating may have resulted from using this method for individual countries, the estimates for world regions should not be biased. We found a strong correlation between GNI and overweight and obesity prevalence in our analysis. For example, the correlation between GNI and overweight was 0.62 with a P-value of less than 0.0001. Furthermore, these countries include less than 12% of the world population. The methods that we used to estimate the variance of absolute numbers of overweight and obese persons were conservative. Therefore, the confidence intervals could be smaller than those we reported. Owing to limitations in the data available from peer-reviewed journal articles, our analysis also included data from government publications. However, a sensitivity analysis limited to data from only peer-reviewed journal articles showed very similar estimates of worldwide prevalence and absolute numbers of overweight and obese individuals.
We projected the global burden of overweight and obesity in 2030 under two distinct assumptions: (1) the age-specific prevalence of overweight and obesity in each world region by gender and urbanization would remain stable, and (2) the age-specific prevalence of overweight and obesity in each world region by gender and urbanization would continuously increase based on recent secular trends. Existing data suggest that the prevalence of overweight and obesity is increasing in many developed and developing countries and these changes are likely to continue over the next few decades.10 Therefore, the former estimates may be very conservative. However, projections of future prevalence based on past trends may not be always appropriate and, thus, the latter estimates also carry a degree of uncertainty. Owing to restrictions in the data collected, estimates accounting for urbanization increases could only be calculated for Sub-Saharan Africa, China, India, and other Asia and Islands. Changes in urbanization level, however, are anticipated to be less than 10% for all other world regions.8
In our study, common criteria for overweight and obesity were used in all world regions. The WHO expert consultation recognized the higher prevalence of type 2 diabetes and other risk factors for cardiovascular disease at lower levels of body weight in Asian populations and recommended lower cutoff points of BMI (⩾23 kg/m2 for overweight and ⩾27.5 kg/m2 for obesity).11 However, most studies conducted in Asian populations have used a BMI ⩾25 kg/m2 for overweight and ⩾30 kg/m2 for obesity. In addition, the only two published large prospective cohort studies investigating the association between mortality and BMI in Asian populations indicated that the relationship is similar to those observed in Western populations and suggested a common criteria for defining overweight and obesity in all populations.12, 13
A previous report from the WHO estimated that there were a total of 750 million overweight and 300 million obese adults in the year 2000.14 Our estimates are 25% greater for overweight and 32% greater for obesity. Different methodologies were used to calculate global totals of overweight/obesity in these studies. In the WHO report, mean BMI values from select countries around the world were converted into overweight and obesity prevalence. This was done using regression equations based on data from a limited number of countries.14 In our study, we only used data from countries that reported prevalence estimates to estimate the total burden of overweight and obesity.
National programs aimed at reducing the prevalence of overweight, obesity, and related co-morbidity and mortality have been launched in some economically developed countries.15 Unfortunately, such public health interventions in developing countries are scarce. Initiatives in these regions would be particularly beneficial as most overweight and obese individuals will reside in the developing world. The challenge of weight reduction combined with its costliness makes primary prevention of overweight and obesity a more feasible and cost-effective alternative for curbing the obesity epidemic, particularly in areas where healthcare resources are limited. A reduction in the global burden of overweight and obesity will translate into worldwide decreases in diabetes, cardiovascular disease, cancer, all-cause mortality and other associated complications.
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This study was partially supported by a grant (R01 HL68057) from the National Heart, Lung, and Blood Institute, Bethesda, MD, USA. Dr Reynolds was partially supported by a Building Interdisciplinary Research Careers in Women's Health Scholarship (K12 HD43451) cofunded by the Office of Research on Women's Health (ORWH) and the Office of Dietary Supplements (ODS), National Institutes of Health, Bethesda, MD, USA.
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Kelly, T., Yang, W., Chen, CS. et al. Global burden of obesity in 2005 and projections to 2030. Int J Obes 32, 1431–1437 (2008). https://doi.org/10.1038/ijo.2008.102
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