42 Introduction to Human Nutrition
Individuals who have sedentary occupations and
do not participate frequently in leisure pursuits that
require physical activity probably have a PAL factor
in the region of 1.4. Those who have occupations
requiring light activity and participate in light physi-
cal activities in leisure time probably have a PAL
around 1.6 (this is a typical value for sedentary people
living in an urban environment). Individuals who
have physically active occupations and lifestyles prob-
ably have a PAL greater than 1.75. It has been sug-
gested that the optimal PAL that protects against the
development of obesity is around 1.8 or higher.
Increasing one’s physical activity index from 1.6 to
1.8 requires 30 min of daily vigorous activity, or
60 min of light activity (Table 3.4).
3.6 Energy balance in various conditions
Infancy and childhood
Changes in energy intake during infancy have been
well characterized. During the fi rst 12 months of life,
energy intake falls from almost 525 kJ/kg per day in
the fi rst month of life to a nadir of 399 kJ/kg per day
by the eighth month, then rises to 441 kJ/kg per day
by the 12th month. However, total energy expendi-
ture in the fi rst year of life is relatively constant at
around 252–294 kJ/kg per day. In infants, the large
difference between total energy expenditure and
energy intake is explained by a positive energy balance
to account for growth. In the fi rst 3 months of life it
is estimated that the energy accretion due to growth
is 701.4 kJ/day, or approximately 32% of energy
intake, falling to 151.2 kJ/day, or 4% of energy intake,
by 1 year of age. Individual growth rates and early
infancy feeding behavior are at least two known
factors that would cause variation in these fi gures.
There is now substantial evidence to suggest that
existing recommendations may overestimate true
energy needs, based on measurement of total energy
expenditure in infants. In the fi rst year of life, tradi-
tional values of energy requirements overestimate
those derived from measurement of total energy
expenditure and adjusted for growth by 11%. Between
1 and 3 years of age the discrepancy is more striking,
where the traditional values for requirements are 20%
higher than those derived from total energy expendi-
ture and adjusted for growth. For example, in 3 year
old children total energy expenditure by DLW aver-
ages 5.1 MJ/day, while the currently recommended
intake for these children is 6.2 MJ/day. Thus, newer
estimates of the energy requirements of infants are
needed based on assessment of total energy expendi-
ture data.
Several laboratories have reported measurements
of total energy expenditure in young, healthy, free-
living children around the world. Despite marked dif-
ferences in geographical locations, the data are similar,
although environmental factors such as season and
sociocultural infl uences on physical activity can infl u-
ence total energy expenditure and thus energy require-
ments. In the average 5 year old child weighing 20 kg,
total energy expenditure is approximately 5.5–5.9 MJ/
day, which is signifi cantly lower than the existing rec-
ommended daily allowance for energy in children of
this age, by approximately 1.7–2.1 MJ/day. Thus, as
with infants, newer estimates of energy needs in chil-
dren are needed based on assessment of total energy
expenditure data.Aging
In the elderly, two different problems related to
energy balance can be recognized. In one segment of
the elderly population there is a decline in food intake
that is associated with dynamic changes in body com-
position where there is a tendency to lose FFM, which
leads to loss in functionality. In others there is a
tendency to gain fat mass, which increases the risk
for obesity, cardiovascular disease, and noninsulin-
dependent diabetes. These two opposing patterns
suggest that the ability to self-regulate whole body
energy balance may diminish with aging. Thus, pre-
scription of individual energy requirements may serve
as a useful tool to prevent the age-related deteriora-
tion of body composition. Other special consider-
ations in the elderly relate to meeting energy needs in
special populations, such as those with Alzheimer’s
and Parkinson’s disease, which frequently can lead
to malnourished states and a diminishing of body
weight. It was thought that these neurological condi-
tions may lead to body weight loss because of an
associated hypermetabolic condition in which meta-
bolic rate may increase above normal, thus increasing
energy needs. However, more recent studies have
clearly shown that the wasting or loss of body weight
often associated with these conditions is explained by
a reduction in food intake, probably owing to a loss
in functionality.