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Center for Human Nutrition and Department of International Health, Johns Hopkins School of Public Health, Baltimore, MD 21205
2To whom correspondence and reprint requests should be addressed at Johns Hopkins School of Public Health, Center for Human Nutrition and Department of International Health, 615 North Wolfe Street, Baltimore, MD 21205. E-mail: caballero{at}jhu.edu.
| ABSTRACT |
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KEY WORDS: obesity developing countries nutrition transition international nutrition
| INTRODUCTION |
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It is logical to link the increasing obesity rates in developing
countries with a progressive introduction of factors associated with
obesity in developed societies, such as sedentary lifestyle, high fat
and fast foods. But it is also recognized that there are several unique
elements to the nutritional conditions of LDC. First, chronic
malnutrition is common in LDC, leading to lifetime stunting in
significant segments of the population. There is increasing evidence
that malnutrition early in life is one additional risk factor for
obesity and other chronic diseases in the adult (Barker 1992
, Law et al. 1992
, Phillips et al. 1994
). In addition, the fact that a large percentage of the
population may be of low stature resulting from chronic malnutrition
requires careful interpretation of weightheight relationships used
for the diagnosis of obesity, particularly in children. Second,
contrary to DC, food choices in LDC may remain limited, because of
either market limitations or cost (Aguirre 1994
). Third,
low income and limited access to education may pose constraints on
peoples ability to seek and secure healthier foods and lifestyle.
These biological and environmental factors are summarized in
Table 1
.
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| Assessing obesity in populations with high prevalence of undernutrition |
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Whereas the BMI in children (ages 219 in the United States) is based
on patterns of normal growth, the acceptable BMI range in the adult is
based on mortality and morbidity risks. There is increasing recognition
that the BMIrisk correlation, based on U.S. data, may be quite
different in different populations in the developing world. First,
ethnic factors may result in a different body adiposity distribution,
which is itself a major determinant of risk associated with excess body
fat (McKeigue et al. 1991
). Second, since short stature
is an independent risk factor for a number of diseases, this element
must be considered along with BMI in assessing disease risk in
developing country populations.
| Obesity trends in the developing world |
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Because of the limited availability of longitudinal data, Pelletier and
Rahn (1998
) estimated obesity trends by applying a
regression model to cross-sectional data from over 200
cross-sectional studies. A summary of these results is presented in
Figure 1
. Although a general trend toward higher BMIs can be observed, the
characteristics and implications of those changes may be quite
different. For example, in countries like China, gains in BMI move the
population away from borderline undernutrition and well into the normal
BMI range. In contrast, BMI gains in other countries put some segment
of the population, usually the high socioeconomic status group, at risk
of obesity.
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| BIOLOGICAL FACTORS |
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Undernutrition in early life was previously proposed as a
significant risk factor for several adult chronic diseases, some of
them linked to obesity (Barker 1992
, Law et al. 1992
, Phillips et al. 1994
). The review by
Martorell et al. in this symposium discusses this issue, pointing to
different results from a number of studies exploring this association.
The main descriptive studies supporting a positive correlation between
fetal malnutrition and risk of adult diseases such as diabetes,
cardiovascular and pulmonary diseases emerged from data in the United
Kingdom (Barker 1992
) and from a study of records of the
Dutch famine during WWII (Susser and Stein 1994
). The
impact of postnatal growth retardation on obesity risk in the adult is
less clear, and is further discussed in this symposium. Postnatal
growth retardation, however, may also be associated with risk of other
chronic conditions. In a recent report on a 7-y follow-up of
children who were stunted during the first 2 y of life, Gaskin et
al. (2000
) found that children who were stunted at young
age had significantly higher systolic blood pressure at age 78 y;
however, they found no effect of birth weight.
Proponents of the link between early malnutrition and later obesity
suggest that energy deficiency triggers a series of metabolic and
hormonal changes that put the individual at higher risk of excess body
fat accumulation. Some of the endocrine changes associated with
protein-energy malnutrition, such as decreased plasma IGF-1 levels,
increased plasma cortisol and a relative reduction in plasma insulin
concentrations (Torun and Chew 1999
) are consistent with
an inhibitory effect on lipolysis. When more calories become available,
particularly from fat, these hormonal changes may impair the
individuals ability to respond by increasing fat oxidation. A recent
study from Sao Paulo appears to support this possibility, reporting a
significant reduction in fat oxidation (estimated by indirect
calorimetry) in stunted vs. nonstunted children (Hoffman et al. 2000
).
Assessing the association between stunting and later obesity is
complicated by the differential responses of weight and height gain to
increased caloric intake, as discussed above. Early stunting would
facilitate attaining a higher BMI, if recovery in weight with little or
no recovery in height occurs later in childhood. This effect could be
potentiated by a diet limited in micronutrients shown to affect linear
growth, such as zinc (Golden and Golden 1981
).
Genetic factors
For centuries, human survival depended on body fat accumulation
and maximizing energy utilization. Thus, genes favoring minimum energy
expenditure, maximum storage of energy in adipose tissue, were
preferentially activated. In modern society, when the supply of energy
is constant throughout the year and the energy demand of daily work has
greatly decreased, that adaptation has become a severe handicap. This
is the basis of the "thrifty gene" hypothesis, invoked to explain
the remarkable susceptibility to obesity of American Indians
(Byers 1992
). A similar mismatch between atavistic
metabolism and modern lifestyle may conceivably play a role in the
emergence of obesity in LDC. Genetic polymorphism also determines
individual responses to environmental challenges in terms of dietary
intake, nutrient levels and energy balance, and there is much to be
explored in this area in LDC populations. Similarly, familial
clustering of energy expenditure was previously documented among high
obesity populations, showing that families whose members tend to have
lower resting energy expenditure are at increased risk of excess weight
gain in subsequent years (Ravussin et al. 1988
).
| ECOLOGICAL FACTORS |
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Demographic projections for the next 30 y coincide in placing
the burden of population growth primarily on the developing world, and
most of this growth will be in urban areas. According to United
Nations estimates, in the next 25 y the rural population in the
developing world is expected to increase by 6%, while the urban
population will grow by 87% (UN Population Division 1988
). Several studies have pointed out the positive
correlation between urbanization and population BMI and have showed
that, as urbanization advances, the BMI distribution curve of the
population shifts to the right (INCLEN 1996). Studies
comparing growth of children from rural and urban areas also described
higher weight-for-age and height-for-age in urban children. Table 2
presents data from Venezuela, comparing weightage of children from
urban and rural areas (Lopez-Blanco et al. 1992
). It is
of note that urban dwelling seems to improve growth patterns, reducing
the percentage of children with low weight-for-age. However, urban
residence is also associated with a marked increase in the percentage
of children with weight-for-age above the 95th percentile. The
mechanisms of these changes are not well documented, but it can be
suggested that urban children appear to achieve a more positive energy
balance than rural children, allowing them to grow at a better rate.
One can speculate that this may result from a combination of increased
energy intake, decreased energy expenditure and, perhaps, reduced
gastrointestinal nutrient losses.
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The lack of adequate longitudinal data on patterns of physical
activity in the developing world precludes an estimation of trends.
Indirect evidence, however, supports the notion of a reduction in daily
energy expenditure associated with urban living. Many typical rural
survival tasks requiring high energy output, such as hauling wood for
cooking and heating over long distances or steep terrain, are reduced
or eliminated in the urban setting (Torun 2000
). Studies
in rural Guatemala measuring energy expenditures of agricultural
workers reported figures of 27003700 kcal/d, (equivalent to 1.8 to
2.35 x BMR), which can be considered from moderately heavy to
very heavy (Viteri and Torun 1975
). In contrast, the
predominance of service-type jobs in urban areas may result in
lower labor energy demands. The increasing role of service work in LDC
was pointed out by Popkin et al. (1999
). Using a
time-series regression model to analyze employment data, they
reported that urbanization is associated with an increasing shift of
the labor force toward service-type jobs, with a concomitant
reduction in agriculture-type jobs. From these results, it can be
inferred that work energy expenditure would tend to be lower in the
urban than in the rural environment.
Besides labor energy demands, there is also some evidence that a
sedentary lifestyle is common among low income urban dwellers. Over
10 y ago, a PAHO report in six Latin American cities (Pan American Health Organization 1986
) found sedentary lifestyle in
4070% of men and 6582% of women. More recently, a survey in
Panama City found that 50% of men and 75% of women engaged in little
or no regular exercise (Torun 2000
).
Food availability and dietary intake
The traditional association between per capita income and dietary
patterns, described in a global WHO report over 30 y ago, was one
in which lower incomes were associated with lower fat, lower animal
protein and higher complex carbohydrate intakes, whereas consumption of
total and animal fat increased as income level went up (WHO 1990
). Analyzing food balance data from LDC, Drewnowski and
Popkin (1997
) suggested that the classical correlation
between income and dietary patterns has been drastically changed by the
globalization of food production and marketing. Even lower income
countries appear to consume a higher percentage of calories from fat, a
fact attributed to the widespread availability and low cost of
vegetable oils (Beare-Rogers et al. 1998
). Whether an
increased dietary energy density results in a higher caloric intake is
still unclear, and some reports describe lower rather than higher total
dietary energy intake in the urban setting (Alarcon and Adrino 1991
).
In DC increasing numbers of dietary calories are consumed outside the
home (Frazao 1999
). Some of the apparent reasons for
this trend, such as women working outside the home, and ease and lower
cost of fast foods, may also apply to LDC in transition. This issue is
important because fast foods and low cost restaurant foods tend to have
a higher fat content than home-prepared foods (Frazao 1999
).
The overall impact of these environmental changes on obesity risk has
been documented in many situations and cultures. The evolution of
obesity among American Indian communities is a case in point. For
example, the prevalence of overweight (BMI > 85th percentile) in
children 512 y of age in the White Mountain Apache reservation
increased from 14% in 1974 to 48% in 1992. In that relatively short
time span, major economic and social changes occurred in that
community, with transition from physical to mechanized transportation,
increasing proportion of service jobs and introduction of processed
foods, supermarkets, television and other forms of sedentary leisure
activities (Owen et al. 1981
, Nelson 1994
). Exposure to a "Western-style" living environment has
a similar effect, as documented in a comparison of Pima Indians living
in rural Mexico with Pimas living near Phoenix, a large urban area in
Arizona (Ravussin et al. 1994
). Although from identical
genetic pool, Pimas living in Arizona had an average BMI 10 points
higher than that of their Mexican counterparts, who live in a more
traditional, semirural environment.
There is no question that, for many LDC, gains in average
population BMI are desirable and may reflect improved socioeconomic
conditions. The economist Robert Fogel documented the
centuries-long struggle of humankind to overcome undernutrition and
attain a body size that increases productivity and protects from
premature death (Fogel 1986
). Using Whaaler surface
plots to correlate stature, BMI and mortality risk, Fogel tracked the
secular trends in body size in humans over the past several centuries.
Figure 2
presents the evolution of body size in the French population since 1705
(Fogel 1997
), showing that secular gains in BMI resulted
from combined gains in weight and in height. In LDC, the nutrition
transition is facilitating rapid gains in body weight in low income and
undernourished populations. But unless there is a concurrent reduction
in childhood stunting and an improvement in adult stature, normalizing
BMIs will not confer the same reduction in mortality risk as that in DC
populations. Continuing gains in BMI beyond the normal range will
potentiate the risk associated with low stature. Thus, whereas in DC
reducing the health risk associated with obesity demands a focus on
controlling excess body weight, in LDC that task will also demand a
major effort to combat chronic childhood malnutrition, to increase the
stature of future generations of adults.
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| FOOTNOTES |
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