Environmental Engineering Reference
In-Depth Information
months of lactation, the cost would average 2.8 MJ/day.
A typical Western woman would start breastfeeding with
some 150 MJ of fat reserves that will be converted to
milk during the following six months, so the actual addi-
tional energy cost is only about 2.1 MJ/day. Still, this is
nearly twice the extra energy needed in pregnancy, and
the 370 MJ needed for half a year of breastfeeding repre-
sents a higher energy cost than carrying a baby to term
after 280 days.
International consensus on how to combine these food
energy needs and recommend desirable daily intakes has
undergone a number of adjustments since the periodic
standard-setting meetings of nutritional experts begun
shortly after WW II. The first two international commit-
tees put the needs of a reference man (25 years old,
weighing 65 kg, and living in a temperate zone) at 13.4
MJ/day and those of a reference woman (25 years old,
weighing 55 kg) at 9.6 MJ/day (FAO 1957). The third
committee redefined the reference adults: still at 65 and
55 kg, but 20-39 years old, healthy, working moderately
for 8 h, sleeping 8 h, spending 4-6 h in very light activ-
ities, and moving or engaging in active recreation or
household duties for the remaining time (FAO 1973).
These moderately active adults needed, respectively,
12.5 MJ/day and 9.2 MJ/day. A multiplier of 0.9 was
selected for light work, 1.17 for very active, and 1.34
for exceptionally active exertions. The 1985 consensus
meeting adopted a different approach by expressing total
energy requirements as multiples of the BMR (FAO
1985).
The latest consensus report (FAO 2004) continued
that approach for adults but relied on DLW or HRM
studies in setting the standards for infants, children, and
adolescents. The advantage of the latter approach is par-
ticularly clear when estimating the energy requirements
of infants because their BMRs are so highly variable,
ranging from 180 kJ/g/day to 250 kJ/g/day. The new
equation to calculate the TEE of infants from birth to 12
months of age is valid for both sexes:
TEE
ð
MJ
=
day
Þ¼
0
:
416
þ
0
:
371 kg
:
Measurements show that the TEE of breastfed infants is
lower than that of babies fed a formula. Equations for the
TEE of children and adolescents are sex-specific:
TEE
ð
MJ
=
day
Þ¼
1
:
298
þ
0
:
265 kg
ð
boys
Þ
TEE
ð
MJ
=
day
Þ¼
1
:
102
þ
0
:
273 kg
ð
girls
Þ
:
As the children grow, their specific energy requirements
decline linearly between ages 2 and 18, from about 350
kJ/kg/day to about 200 kJ/kg/day for boys, and from
about 340 kJ/kg/day to 180 kJ/kg/day for girls. Sup-
plementary food for catch-up growth of children with
weight deficit requires about 21 kJ/g of newly added
tissue.
Adult requirements are based on factorial estimates
of habitual TEE. These, in turn, are derived from the
average BMR and the PAL attributable to a particular
population, and the 24-h PAL takes into account both
occupational and leisure activities (FAO 2004). The min-
imal survival requirement for people who are not bedrid-
den can be calculated by assuming 8 h of sleep and rest
for the remainder of the day, except for token moving
and standing briefly while washing and dressing; this
gives PAL of 1.27. Survival minima for most adults
would thus be between 6.2 MJ/day (50-kg woman)
and 9.6 MJ/day (80-kg man), fluxes of about 70-110
W. Beyond these minimal requirements lies an endless
