44 Introduction to Human Nutrition
Energy requirements in disease and trauma
The DLW technique has been used in various studies
to assess the energy requirements of hospitalized
patients. Information on energy requirements during
hospitalization for disease or trauma is important
because:
● energy expenditure can be altered by the disease or
injury
● physical activity is often impaired or reduced
● both underfeeding and overfeeding of critically ill
patients can lead to metabolic complications; there-
fore, correct assessment of energy requirements
during recovery is an important part of therapy.
The metabolic response during recovery from a
burn injury includes an increase in RMR, although
this is not necessarily a function of the extent of the
burn. The widely used formulae to predict energy
needs in burn patients are not based on measurement
of energy expenditure and estimate that most patients
require 2–2.5 times their estimated RMR. However,
using the DLW technique, total energy expenditure
was 6.7 + 2.9 MJ/day in 8 year old children recovering
from burn injury, which was equivalent to only 1.2
times the nonfasting RMR. The lower than expected
values for total energy expenditure in children recov-
ering from burns suggest that RMR is not as elevated
in burn patients as previously speculated, and that
RMR is not a function of burn size or time after the
injury, probably owing to improvements in wound
care which reduce heat loss. In addition, energy
requirements in patients recovering from burn injury
are reduced because of the sedentary nature of their
hospitalization.
In a study of patients with anorexia nervosa, total
energy expenditure was not signifi cantly different
than controls (matched for age, gender, and height).
However, physical activity-related energy expendi-
ture was 1.3 MJ/day higher in anorexia nervosa
patients, which was compromised by a 1.3 MJ/day
lower RMR. Thus, energy requirements in anorexia
nervosa patients are normal, despite alterations in the
individual components of total energy expenditure.
In infants with cystic fi brosis, total energy expendi-
ture was elevated by 25% relative to weight-matched
controls, although the underlying mechanism for this
effect is unknown.
Developmental disabilities appear to be associated
with alterations in energy balance and nutritional
status at opposite ends of the spectrum. For example,
cerebral palsy is associated with reduced fat mass and
FFM, whereas half of patients with myelodysplasia are
obese. It is unclear whether the abnormal body com-
position associated with these conditions is the end-
result of inherent alterations in energy expenditure
and/or food intake, or whether alterations in body
composition are an inherent part of the etiology of
the specifi c disability. In addition, it is unclear how
early in life total energy expenditure may be altered
and whether reduced energy expenditure is involved
with the associated obese state. Nevertheless, pre-
scription of appropriate energy requirements may be
a useful tool in the improvement of nutritional status
in developmental disabilities.
Total energy expenditure has been shown to be
lower in adolescents with both cerebral palsy and
myelodysplasia, partly owing to reduced RMR but
primarily to reduced physical activity. Based on
measurements of total energy expenditure, energy
requirements of adolescents with cerebral palsy and
myelodysplasia are not as high as previously specu-
lated. In nonambulatory patients with cerebral palsy,
energy requirements are estimated to be 1.2 times
RMR, and in the normal range of 1.6–2.1 times RMR
in ambulatory patients with cerebral palsy.3.7 Obesity
Basic metabolic principles
Obesity is the most common form of a disruption in
energy balance and now constitutes one of the major
and most prevalent disorders of nutrition. Because of
the strong relationship between obesity and health
risks, obesity is now generally considered a disease by
health professionals.
Although the body continuously consumes a mixed
diet of carbohydrate, protein, and fat, and sometimes
alcohol, the preferred store of energy is fat. There is
a clearly defi ned hierarchy of energy stores that out-
lines a preferential storage of excess calories as fat. For
alcohol, there is no storage capacity in the body. Thus,
alcohol that is consumed is immediately oxidized for
energy. For protein, there is a very limited storage
capacity and, under most situations, protein metabo-
lism is very well regulated. For carbohydrate there is
only a very limited storage capacity, in the form of
glycogen, which can be found in the liver and in