Agriculture Reference
In-Depth Information
C h a n g i n g P of P u L a t i of n s t r u C t u r e s
The last two decades have seen major decreases in fertility and increases in life
expectancy in most parts of the world, including all areas with the single exception
of parts of sub-Saharan Africa and perhaps Haiti. The rapid population growth that
characterized the period from about 1700 to the present is projected to slow mark-
edly in the next few decades. Population growth is forecast to continue for about the
next 50 years, with the world's population stabilizing at somewhere between 8 and
12 billion (Zlotnik 2002). The period of continued growth that will characterize the
next few decades will be very uneven across regions. For example, fertility rates in
Europe are already below replacement levels, while some regions of the developing
world still have very high fertility rates. In most of the developing world, however,
fertility is declining dramatically, and life expectancies have increased markedly in
the last few years. The consequence is that populations are aging—the proportion
comprised of adults is higher and that comprised of children lower. In terms of dis-
ease burden and health care needs, this means that health problems of adulthood are
becoming more important.
The shift in population structure will be a crucial driver of income growth in
many developing countries; with more adults, a larger portion of populations will
be economically active, earning incomes that are spent raising a smaller number of
children. The implications for the obesity epidemic are already evident. In China, 20
years of a one-child population policy and a growing economy have meant that fami-
lies invest more resources in a single child. A sharp rise in childhood overweight has
been seen already (Jing 2000).
u r b a in i z a t i o in
Even more dramatic than the slowdown in overall population growth is the shift
to a largely urbanized world. Cities are home to almost half the world's popula-
tion, up from only 30% as recently as 1950 (Zlotnik 2002), and virtually all of the
projected population growth globally in the next 20 years will be urban. Life in
cities involves major differences in both diet and energy expenditure from life in
rural areas. The effect on physical activity patterns is generally profound. Children
and young adults spend more time in school as countries invest in education for
all; adults are likely to work in service sector, marketing, managerial, or profes-
sional occupations rather than agriculture; transportation systems, including buses
and automobiles, replace more energy-demanding walking and carrying; high-rise
apartment buildings provide little or nothing in the way of space for active play for
children; and television sets and computers are increasingly the centers for leisure
time. The net effect is a decline in physical activity, fitness, and energy expenditure
on a striking scale. Urbanization generally also means more female participation in
the workforce and consequent change in food intake patterns within the home, away
from time-intensive traditionally prepared meals toward more convenient meals and
snacks (Schmidhuber and Shetty 2004). And, compared to rural populations, city
dwellers globally consume diets that are higher in fat, animal products, sugar, and
processed foods and lower in unrefined grains (Popkin 2002).
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