Walpole et al. BMC Public Health 2012, 12:439
`http://www.biomedcentral.com/1471-2458/12/439
`
`RE S EA R C H A RT I C L E
`Open Access
`The weight of nations: an estimation of adult
`human biomass
`Sarah Catherine Walpole1*, David Prieto-Merino2, Phil Edwards2, John Cleland2, Gretchen Stevens3
`and Ian Roberts2
`
`Abstract
`
`Background: The energy requirement of species at each trophic level in an ecological pyramid is a function of the
`number of organisms and their average mass. Regarding human populations, although considerable attention is
`given to estimating the number of people, much less is given to estimating average mass, despite evidence that
`average body mass is increasing. We estimate global human biomass, its distribution by region and the proportion
`of biomass due to overweight and obesity.
`Methods: For each country we used data on body mass index (BMI) and height distribution to estimate average
`adult body mass. We calculated total biomass as the product of population size and average body mass. We
`estimated the percentage of the population that is overweight (BMI > 25) and obese (BMI > 30) and the biomass
`due to overweight and obesity.
`Results: In 2005, global adult human biomass was approximately 287 million tonnes, of which 15 million tonnes
`were due to overweight (BMI > 25), a mass equivalent to that of 242 million people of average body mass (5% of
`global human biomass). Biomass due to obesity was 3.5 million tonnes, the mass equivalent of 56 million people of
`average body mass (1.2% of human biomass). North America has 6% of the world population but 34% of biomass
`due to obesity. Asia has 61% of the world population but 13% of biomass due to obesity. One tonne of human
`biomass corresponds to approximately 12 adults in North America and 17 adults in Asia. If all countries had the BMI
`distribution of the USA, the increase in human biomass of 58 million tonnes would be equivalent in mass to an extra
`935 million people of average body mass, and have energy requirements equivalent to that of 473 million adults.
`Conclusions: Increasing population fatness could have the same implications for world food energy demands as
`an extra half a billion people living on the earth.
`
`Background
`Thomas Malthus’ Essay on the Principle of Population
`warned that population increase would eventually outstrip
`food supply, resulting in famine [1]. Malthus expressed his
`concern at a time when the amount of food energy that
`could be harvested from a given amount of land was con-
`strained by the available agricultural technologies. The
`Green Revolution of the twentieth century challenged
`Malthus’ grim predictions, as fossil fuel-based fertilizers,
`pesticides, irrigation and mechanization greatly increased
`food yields [2]. In the twenty first century, the link be-
`tween population and ecological sustainability is again
`
`* Correspondence: argotomunky@yahoo.co.uk
`1Foundation Year 2 doctor, North Yorkshire and East Coast deanery, 4 Hilton
`Place, Leeds LS8 4HE, UK
`Full list of author information is available at the end of the article
`
`coming to the fore, as global food yields are threatened by
`ecological destruction (including climate change) and as
`world population grows [2].
`The energy requirement of species at each trophic level
`in an ecological pyramid is a function of the number of
`organisms and their average mass. In ecology, these fac-
`tors are often considered together by estimating species bio-
`mass, the total mass of living organisms in an ecosystem. In
`relation to human populations, although much attention is
`given to the effect of population growth on food energy
`requirements, much less attention is given to the impact
`of increasing body mass.
`Physical activity accounts for 25-50% of human energy
`expenditure. Due to the greater energy cost of moving a
`heavier body, energy use increases with body mass [3].
`Resting energy expenditure also increases with body
`
`© 2012 Walpole et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
`Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
`reproduction in any medium, provided the original work is properly cited.
`
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`mass, due to the increase in metabolically active lean tis-
`sue that accompanies increases in body fat [4]. As for
`other organisms, the energy requirements of human
`populations depend on species biomass. Currently, more
`than a billion adults are overweight and in all regions of
`the world,, the entire population distribution of body
`mass is moving upwards [5].
`The increased global demand for food arising from the
`increase in body mass is likely to contribute to higher
`food prices. Because of the greater purchasing power of
`more affluent nations (who also have higher average
`body mass), the worst effects of increasing food prices
`will be experienced by the world’s poor. In this article,
`we estimate total human biomass,
`its distribution by
`world region and the proportion of human biomass at-
`tributable to overweight and obesity.
`
`Methods
`Data sources
`For each country, we obtained estimates of the popula-
`tion in 2005 by age and sex from the United Nations
`population database [6]. We obtained estimates of mean
`(and SD) body mass index (BMI) from the WHO SURF2
`report [7] and estimates of mean height (and SD) for 190
`countries from national health examination surveys, pri-
`marily the Demographic and Health Surveys [5]. Because
`surveys were not conducted in every country, height data
`were not available by age and sex in some countries. To
`estimate mean height (and SD) by age and sex in every
`country using the available data, we built a linear regres-
`sion model (of age-sex group, average height, WHO region
`and sub-region) using R open access statistical software.
`Some countries and territories were excluded from the
`analysis due to insufficient data on BMI (see Table 1 for a
`list of these).
`
`Biomass estimation
`Total biomass by age-sex group was estimated as the
`product of the number of people in the group and their
`average body mass. The formulae for the estimation of
`body mass are given below Table 1. We also estimated
`total biomass due to overweight in each age-sex group.
`We assumed that BMI is normally distributed in the
`group and estimated the number of people overweight
`(using prevalence of BMI > 25) and their average BMI.
`Using their average BMI, we then estimated their average
`body mass. The biomass of overweight people was calcu-
`lated as the product of the number of overweight people
`and their average body mass. Biomass due to overweight
`was calculated by estimating the biomass of overweight
`people assuming they had BMI of 25 and subtracting this
`from their actual biomass. Using a similar method we esti-
`mated the biomass due to obesity. We calculated the total
`biomass of obese people in each age-sex group and
`
`Table 1 List of excluded countries due to insufficient data
`on BMI
`Country / Territory
`Other non-specified areas (Taiwan)
`
`Adult pop. (2005)
`18,405,317
`
`UN code
`158
`
`Serbia
`
`China, Hong Kong SAR
`
`Puerto Rico
`
`Occupied Palestinian Territory
`
`Réunion
`
`Montenegro
`
`China, Macao SAR
`
`Guadeloupe
`
`Martinique
`
`Western Sahara
`
`French Polynesia
`
`New Caledonia
`
`Netherlands Antilles
`
`French Guiana
`
`Channel Islands
`
`Guam
`
`Mayotte
`
`United States Virgin Islands
`
`Aruba
`
`TOTAL:
`
`688
`
`344
`
`630
`
`275
`
`638
`
`499
`
`446
`
`312
`
`474
`
`732
`
`258
`
`540
`
`530
`
`254
`
`830
`
`316
`
`175
`
`850
`
`533
`
`8,037,649
`
`5,840,953
`
`2,936,606
`
`1,928,679
`
`582,423
`
`502,268
`
`401,495
`
`338,621
`
`313,280
`
`301,959
`
`185,626
`
`168,610
`
`143,172
`
`130,255
`
`124,942
`
`119,046
`
`101,272
`
`84,706
`
`79,238
`
`40,726,117
`
`
`
`Formula for estimating the expected (average) weight (W) in a specific age-sex
`group where mean and variance of BMI and of height.
`Using the following notation for each individual values of BMI and W:
`
`b ¼ BMI BMIð Þ and h ¼ H H
`
`
`ð Þ
`
`
`The expected weight in a group of individuals would be:
`E Wð
`Þ ¼ E BMI  H2
`ð
`
`Þ ¼ E BMI þ bð
`
`Þ  H þ hð Þ2
`
`
`
`¼ E BMI þ bð
`
`Þ  ðH2 þ h2 þ 2HhÞ
`
`¼ E H2BMI þ h2BMI þ 2HhBMI þ H2b þ h2b þ 2Hhb
`¼ H2BMI þ E h2ð
`ÞBMI þ E hð Þ2HBMI þ E bð ÞH2 þ E bh2ð
`
`¼ H2BMI þ E h2ð
`
`ÞBMI þ E bh2ð
`Þ þ E hbð
`Þ2H
`
`Þ þ E hbð
`
`Þ2H
`
`Þ ¼ 0
`Þ ¼ 0⇒E hbð
`ð
`Assuming that Height and BMI are independent: COV H; BM
`Assuming that the variance of Height is constant in all values of BMI:
`ð
`Þ ¼ 0
`
`
`E bh2
`Therefore the above equation simplifies to: E Wð
`Þ ¼BMI  H2 þ V Hð Þ
`
`subtracted their estimated biomass assuming that they all
`had a BMI of 30. For each country, we calculated total
`human biomass, biomass due to overweight and biomass
`due to obesity by adding the estimates for each age-sex
`group. Global totals were calculated by summating across
`countries.
`
`Extreme case scenarios
`We estimated global biomass under two hypothetical
`scenarios. Specifically, we assumed that each country
`had the same BMI distributions as that of [1] Japan and
`
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`
`Table 2 Estimation of Basal Metabolic Rate (BMR) and
`Total Energy Expenditure (TEE) using FAO tables
`Men
`Women
`BMRs
`BMRs
`Kcal/kg
`Kcal/kg
`15.057
`14.818
`
`PAL(*)
`
`1.75
`
`BMRc
`Kcal
`486.6
`
`PAL(*)
`
`1.79
`
`BMRc
`Kcal
`692.2
`
`age
`15-29
`
`to overweight, obesity or the change in biomass that
`would be seen under hypothetical scenarios, was esti-
`mated by multiplying the number of kg by weight
`dependent component of BMR and by the PAL. We did
`all calculations by country and age-sex group applying
`the corresponding coefficients. Then we summed across
`age-sex groups to obtain total energy requirements for
`each country and for the world. To calculate the number
`of average adults that could be sustained with a given
`quantity of biomass we divided the amount of energy
`required to sustain that biomass by the average food en-
`ergy requirement of one human.
`
`Results
`In 2005, total adult human biomass was approximately 287
`million tonnes (Table 3). Biomass due to overweight was 15
`million tonnes, the mass equivalent of 242 million people of
`average body mass (approximately 5% of the world’s popu-
`lation in 2005). Biomass due to obesity was 3.5 million
`tonnes, the mass equivalent of 56 million people of average
`body mass (1.2% of the world’s population). Average body
`mass globally was 62 kg.
`North America has the highest average body mass of
`any continent (80.7 kg). In North America one tonne of
`human biomass corresponds to 12 adults. More than
`70% of the North American population is overweight
`and biomass due to obesity is 1.2 million tonnes. North
`America has 6% of the world’s population but 34% of
`world biomass due to obesity. Asia has the lowest aver-
`age body mass of any continent (57.7 kg). In Asia, one
`tonne of human biomass corresponds to 17 adults. Asia has
`61% of the world’s population but 13% of world biomass
`due to obesity (449 thousand tonnes).
`The average BMI in Japan in 2005 was 22.9. If all
`countries had the same age-sex BMI distribution as
`Japan, total biomass would fall by 14.6 million tonnes, a
`5% reduction in global biomass or the mass equivalent of
`
`30-44
`
`45-59
`
`60-69
`
`70-79
`
`80+
`
`873.1
`
`873.1
`
`587.7
`
`587.7
`
`587.7
`
`11.472
`
`11.472
`
`11.171
`
`11.171
`
`11.171
`
`1.82
`
`1.64
`
`1.61
`
`1.62
`
`1.3
`
`845.6
`
`845.6
`
`658.5
`
`658.5
`
`658.5
`
`8.126
`
`8.126
`
`9.082
`
`9.082
`
`9.082
`
`1.87
`
`1.8
`
`1.69
`
`1.55
`
`1.19
`
`We extracted the following coefficients for our age-sex groups.
`(*) For non overweight adults in USA.
`The estimation of energy requirements of an individual is:
`BMR ¼ BMRc þ BMRs x Weight kgð
`Þ ! TEE ¼ BMR x PAL
`For a group of N individuals of the same age-sex group with a total biomass
`“B”, BMR ¼ N x BMRc þ BMRs x BM kgð
`Þ ! TEE ¼ BMR x PAL
`If that same group had a biomass due to overweight (BMI > 25) of “B25”, the
`energy required to feed that biomass would be:
`BMR25 ¼ BMRs x B25 kgð
`Þ ! TEE25 ¼ BMR25 x PAL
`
`[2] USA. We used the method outlined above but ap-
`plied the BMI of the relevant age-sex group from Japan
`or USA instead of the actual BMI for that age-sex group.
`These countries were chosen because despite being high
`income countries with adequate nutrition,
`they have
`average BMI values close to global extremes. For each
`scenario, we calculated the global biomass and biomass
`due to overweight and obesity.
`
`Population and energy equivalents
`We calculated the food energy required to sustain
`human biomass using formulae and values from the
`FAO [8]. Physical Activity Level (PAL) values for each
`age-sex group are based on non-overweight adults in the
`USA. Total Energy Expenditure (TEE) is estimated as
`the product of Basal Metabolic Rate (BMR) and PAL (see
`Table 2). The energy required to sustain the biomass due
`
`Table 3 Population, body mass and biomass by world region in 2005 and in hypothetical scenarios
`WHO region
`Adult
`Average
`Biomass
`No of people
`Biomass due to
`BMI > 25
`population
`body mass
`(million kg)
`overweight /
`(millions)
`(kg)
`total population
`(million kg)
`2815
`57.7
`24.2%
`4265
`
`162408
`
`Asia
`
`Biomass due to
`BMI > 30
`(million kg)
`449
`
`Europe
`
`Africa
`
`Latin Am. Caribbean
`
`Northern Am.
`
`Oceania
`
`World
`
`Scenario (1): all countries have
`BMI distribution of Japan
`
`Scenario (2): all countries
`have BMI distribution of USA
`
`606
`
`535
`
`386
`
`263
`
`24
`
`4630
`
`4630
`
`4630
`
`70.8
`
`60.7
`
`67.9
`
`80.7
`
`74.1
`
`62.0
`
`58.8
`
`74.6
`
`42895
`
`32484
`
`26231
`
`21185
`
`1815
`
`287017
`272408 (−5%)
`
`55.6%
`
`28.9%
`
`57.9%
`
`73.9%
`
`63.3%
`
`34.7%
`
`22.3%
`
`3836
`
`1464
`
`2431
`
`3297
`
`191
`
`910
`
`340
`
`585
`
`1187
`
`46
`
`15484
`5630 (−64%)
`
`3518
`253 (−93%)
`
`345426 (+20%)
`
`74.0%
`
`53090 (+243%)
`
`18789 (+434%)
`
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`
`235 million people of world average body mass in 2005.
`This
`reduction in biomass would decrease energy
`requirements by an average of 59 kcal/day per adult living
`on the planet, which is equivalent to the energy require-
`ment of 107 million adults. Biomass due to obesity would
`be reduced by 93%.
`The average BMI in USA in 2005 was 28.7. If all coun-
`tries had the same age-sex BMI distribution as the USA,
`total human biomass would increase by 58 million
`tonnes, a 20% increase in global biomass and the equiva-
`lent of 935 million people of world average body mass in
`2005. This increase in biomass would increase energy
`requirements by 261 kcal/day/adult, which is equivalent
`to the energy requirement of 473 million adults. Biomass
`due to obesity would increase by 434%.
`Figure 1 shows the distribution of biomass due to obesity
`for countries with more than 1% of the global human bio-
`mass due to obesity. The two scenarios are also reflected. If
`China had the same BMI distribution as the USA its bio-
`mass due only to obesity would be equivalent to 121% of
`the world total of biomass due to obesity in 2005.
`The energy required to maintain obese biomass corre-
`sponds to the energy requirements of 24 million adults of
`world average body mass (Table 4). The energy required to
`maintain overweight biomass corresponds to the energy
`requirements of 111 million average adults. In the United
`States alone, the energy required to maintain overweight
`biomass corresponds to the energy requirements of 23
`million adults of world average body mass (Table 4). If all
`
`countries had the same BMI distribution as USA, the
`energy required to maintain obese biomass would increase
`by 481%, corresponding to the energy requirements of 137
`million adults. Under this scenario, the energy required to
`maintain overweight biomass corresponds to the energy
`requirements of 406 million adults.
`
`Discussion
`We estimated global human biomass, its regional distri-
`bution and biomass attributable to overweight and obes-
`ity. Our results underscore the need to take body mass
`into account when considering the ecological
`implica-
`tions of population growth. UN world population projec-
`tions suggest that by 2050 there could be an additional
`2.3 billion people. [6] The ecological implications of ris-
`ing population numbers will be exacerbated by increases
`in average body mass.
`Although the largest increase in population numbers is
`expected in Asia and sub-Saharan Africa, our results
`suggest that population increases in the USA will carry
`more weight than would be implied by numbers alone. It
`is predicted that the US population will increase from
`310 million in 2010 to 403 million by 2050 [5]. Most of
`the increase will be due to migration and to the extent
`that migrants adopt the diet and lifestyles of the host
`population, we can reasonably expect that the body
`mass of migrants will rise. Our results show that this
`could have important implications for world energy
`requirements.
`
`Figure 1 Human biomass due to BMI > 30 (Countries with more than 1% of human biomass due to BMI > 30).
`
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`
`Table 4 Adults per tonne biomass and energy used to maintain overweight and obesity
`Thousands of adults of average mass
`Country with more than
`Adults per
`Average tTEE[1]
`Average energy used to
`that could be maintained by the
`100,000 population
`tonne
`Kcal/day/ adult
`maintain biomass due to
`BMI > 25 in kcal/day/adult
`energy required to maintain
`BMI >25
`BMI >30
`
`Heaviest 10
`
`United States
`
`Kuwait
`
`Croatia
`
`Qatar
`
`Egypt
`
`United Arab Emirates
`
`Trinidad and Tobago
`
`Argentina
`
`Greece
`
`Bahrain
`
`Lightest 10
`
`12.2
`
`12.9
`
`13.1
`
`13.0
`
`13.5
`
`13.2
`
`13.8
`
`13.8
`
`13.3
`
`13.6
`
`19.0
`
`2874
`
`2982
`
`2741
`
`3007
`
`2826
`
`3017
`
`2778
`
`2718
`
`2707
`
`2889
`
`2348
`
`243
`
`233
`
`205
`
`204
`
`192
`
`188
`
`177
`
`176
`
`169
`
`168
`
`8
`
`22,509.2
`
`7,886.6
`
`156.6
`
`300.3
`
`51.6
`
`3,733.5
`
`241.2
`
`71.3
`
`1,967.9
`
`636.0
`
`34.8
`
`57.5
`
`53.9
`
`96.0
`
`14.5
`
`1,184.2
`
`62.8
`
`21.7
`
`575.7
`
`159.3
`
`9.7
`
`1.5
`
`North Korea
`
`Cambodia
`
`Burundi
`
`Nepal
`
`Democ. Rep. of the Congo
`
`Bangladesh
`
`Sri Lanka
`
`Ethiopia
`
`Viet Nam
`
`Eritrea
`
`WORLD 2005
`
`17.9
`
`18.5
`
`19.8
`
`18.7
`
`20.2
`
`19.8
`
`18.9
`
`19.7
`
`19.2
`
`16.1
`
`Scenario (1) if BMI as Japan in all countries 17.0
`
`Scenario (2) if BMI as USA in all countries
`
`13.4
`
`2472
`
`2421
`
`2354
`
`2410
`
`2342
`
`2318
`
`2408
`
`2341
`
`2393
`
`7
`
`7
`
`7
`
`6
`
`5
`
`5
`
`3
`
`3
`
`2
`
`23.9
`
`11.4
`
`42.4
`
`71.2
`
`178.2
`
`27.5
`
`52.9
`
`73.7
`
`2.0
`
`0.2
`
`0.4
`
`0.6
`
`2.2
`
`2.7
`
`0.3
`
`0.5
`
`1.1
`
`0.0
`
`2549
`2490 (−2.4%)
`2810 (+10.2%)
`
`61
`
`22
`
`224
`
`111,346
`40,519 (−64%)
`406,255 (+265%)
`
`23,533
`1,726 (−93%)
`136,721 (+481%)
`
`(1) tTEE = theoretical Total Energy Expenditure calculated from FAO tables for adults, assuming that Physical Activity Levels (PAL) for each age-sex group in all
`countries were the same as those reported for USA in the same document. (2) To calculate these two columns we use the average theoretical tTEE of the world in
`2005 (2549 kcal/day).
`
`In Africa and Asia urban populations are increasing
`more rapidly than rural populations [9]. This will also have
`implications for average body mass [10]. Given the current
`trend of rising BMI, our scenario where all countries have
`a similar BMI distribution to the USA provides an insight
`into possible future challenges. If global biomass were to
`increase to a level where all countries had the age-sex BMI
`distributions of the USA, the biomass increase would be
`equivalent to an extra billion people of average body mass.
`Although, this is not the same as an extra billion people in
`terms of energy requirements, the increase corresponds to
`the energy requirements of about 473 million adults of
`current world average body mass.
`Our findings should be viewed in the light of the fol-
`lowing limitations. Firstly,
`in countries where data on
`average BMI, height and its standard deviation were
`
`unavailable, we used a regression model to estimate the
`missing parameters. Due to limited data availability, we
`assumed that height and BMI are independent variables,
`and that the mean and standard deviation of height are
`the same across the distribution of BMI. Furthermore,
`because of the lack of data describing the distribution of
`BMI in relation to high, we assumed zero covariance be-
`tween BMI and height squared. Secondly, we assumed
`symmetrical (normal) distributions of BMI in each popu-
`lation, when in reality many population distributions will
`be skewed, with a tail to the right of the distribution
`comprising a relatively small proportion of people with
`very high body mass. We may therefore have underesti-
`mated total biomass. Finally, we did not estimate bio-
`mass in children who comprise a significant proportion
`of the population in many countries, nor in countries in
`
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`
`Table 1. Future work in this area should account for
`education levels and urbanisation.
`There are also limitations in our estimates of energy
`requirements. We have used FAO data to estimate the
`BMR but the extent to which they can be applied to all
`populations is open to question. The assumption of simi-
`lar physical activity levels in all countries is clearly un-
`realistic with higher physical activity levels
`in low
`income countries. As a result, we will have underesti-
`mated energy requirements in some countries. However,
`this approach is appropriate for comparing different sce-
`narios of BMI distribution and its implications on rela-
`tive changes in energy requirements.
`
`Conclusions
`Increasing biomass will have important implications for
`global resource requirements,
`including food demand,
`and the overall ecological footprint of our species. Future
`work will investigate the extent to which food demand
`and carbon emissions are likely to increase with increas-
`ing biomass.
`Although the concept of biomass is rarely applied to
`the human species, the ecological
`implications of
`in-
`creasing body mass are significant and ought to be taken
`into account when evaluating future trends and planning
`for future resource challenges. Our scenarios suggest
`that global trends of increasing body mass will have im-
`portant resource implications and that unchecked,
`in-
`creasing BMI could have the same implications for world
`energy requirements as an extra 473 million people.
`Tackling population fatness may be critical to world food
`security and ecological sustainability.
`
`Competing interests
`The authors declare that they have no competing interests.
`
`Acknowledgements
`We thank Marc Levy and Kate Jones for comments on an earlier draft.
`
`Author details
`1Foundation Year 2 doctor, North Yorkshire and East Coast deanery, 4 Hilton
`Place, Leeds LS8 4HE, UK. 2Faculty of Epidemiology and Population Health,
`London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E
`7HT, UK. 3Department of Health Statistics and Informatics, World Health
`Organization, 20 Avenue Appia, Geneva 27 1211, Switzerland.
`
`Authors’ contributions
`GS is a staff member of WHO. The author alone is responsible for the views
`expressed in this publication and they do not necessarily represent the
`decisions, policy, or views of WHO. IR devised the study; SW, DP and PE
`conducted the analyses with input from GS; and all authors contributed to
`writing and revising the manuscript. All authors read and approved the final
`manuscript.
`
`Received: 18 November 2011 Accepted: 18 June 2012
`Published: 18 June 2012
`
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`doi:10.1186/1471-2458-12-439
`Cite this article as: Walpole et al.: The weight of nations: an estimation
`of adult human biomass. BMC Public Health 2012 12:439.
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