Environmental Engineering Reference
In-Depth Information
(A small fraction of 1% of total energy is still needed for
the renewal of adult tissues, principally sloughing skin
and intestinal lining, and growing nails and hair.) The
growth requirement is composed of the energy needed
to synthesize new tissues (fat and protein) and the energy
deposited in them. As the share of fat in newly deposited
tissues declines, so does the energy accrued in normal
growth,
from about 25 kJ/g during the first
three
months to about 11 kJ/g by 12 months of age.
Adequate energy intake in early childhood is essential
not only for transforming us from a state of immobile de-
pendence to one of active exploration but to make us hu-
man. The neonate brain (at about 350 g, twice as large as
that of a newborn chimpanzee) enlarges 3.5 times by the
age of 5 to become more than three times as massive as
the brain of our closest primate species (Foley and Lee
1991). Average childhood weights at particular ages
differ appreciably among countries; better nutrition has
been pushing them higher in most affluent nations over
time. Long-term Japanese trends are an excellent illustra-
tion of this universal trend. Between 1900 and 2000, 11-
year-old Japanese boys gained nearly 20 cm of height,
with the hungry years of World War II representing the
only interruption of a steady rise (fig. 5.4).
The increased energy needs of pregnancy are due not
only to the growth of fetus, placenta, and maternal tis-
sues (uterus, breasts, blood, fat) but also to the rise of
BMR and the cost of increased cardiovascular and respi-
ratory effort during activity. Large data sets show that de-
sirable birth weights of 3.1-3.6 kg are associated with
total maternal weight gain of 10-14 kg (FAO 2004).
This means that the total average weight gain of 12.5 kg
(baby's 3.4 kg, deposition of 925 g of protein and 3.8 kg
of fat) costs about 335 MJ (Hytten 1980), or almost 27
kJ/g. FAO (2004) put it at 321 MJ, or about 0.35 MJ/
5.4 Average height of 11-year-old Japanese boys increased
by nearly 20 cm during the course of the twentieth century.
Plotted from survey data published regularly in Japan's Statisti-
cal Yearbook.
day, 1.2 MJ/day, and 2.0 MJ/day for respective trimes-
ters. Average increases in BMR during the trimesters are
on the order of 5%, 10%, and 25%, respectively, and the
total BMR increment for the 12-kg weight gain is about
150 MJ.
The energy cost of lactation varies considerably with
the volume and duration of milk production. The metab-
olizable energy of human milk is 2.59 kJ/ml (protein
8.9 g/L, 3.2% fat). In affluent countries the median
milk production (with exclusive breastfeeding) rises from
about 700 mL/day during the first month to 850 ml/
day in the sixth month and declines afterward to around
500 mL/day by the end of the first year (FAO 2004).
Conversion of food energy to milk has a high, 80%-
85%, efficiency. With a daily mean of 800 mL for six
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