Livro DRI 2006 (Micronutrientes)

Livro DRI 2006 (Micronutrientes)


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BMR is
usually lower in African Americans than Caucasians. Currently, insufficient data
exist to create accurate prediction equations of BMRs for African American adults.
In this publication, the general prediction equations in Table 1 are used for all
races, recognizing their potential to overestimate BMR in some groups such as
African Americans.
Environment: There is a modest 2\u20135 percent increase in sedentary TEE at low-
normal environmental temperatures (20\u201328\u221eC, or 68\u201382\u221eF) compared with
high-normal temperatures (28\u201330\u221eC, or 82\u201386\u221eF). However, in setting energy
requirements, no specific allowance was made for environmental temperatures.
The TEE values used to predict energy requirements can be considered values
that have been averaged for the environmental temperatures of different sea-
sons. High altitude also increases BMR and TEE due to the hypobaric hypoxia.
However, it is unclear at which heights the effect becomes prominent.
Adaptation and accommodation: Adaptation implies the maintenance of essen-
tially unchanged functional capacity in spite of some alteration in a steady-state
condition, and it involves changes in body composition that occur over an ex-
tended period of time. The term adaptation describes the normal physiological
responses of humans to different environmental conditions. An example of ad-
aptation is the increase in hemoglobin concentration that occurs when indi-
viduals live at high altitudes.
Accommodation refers to relatively short-term adjustments that are made
to maintain adequate functional capacity under altered steady-state conditions.
The term accommodation characterizes an adaptive response that allows sur-
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
PART II: ENERGY 91
vival but results in some consequences on health or physiological function. The
most common example of accommodation is a decrease in growth velocity in
children. By reducing growth rate, children\u2019s bodies are able to save energy and
may subsist for prolonged periods of time on marginal energy intakes, although
this could be at the cost of eventually becoming stunted. The estimation of
energy requirements from energy expenditure implicitly assumes that the effi-
ciency of energy use is more or less uniform across all individuals, an assump-
tion that is supported by experimental data.
The UL
The Tolerable Upper Intake Level (UL) is the highest daily nutrient intake that
is likely to pose no risk of adverse effects for almost all people. The UL concept
does not apply to energy because intake above an individual\u2019s energy require-
ments would lead to weight gain and likely increased risk of morbidity.
EFFECTS OF UNDERNUTRITION
Undernutrition is still a common health concern in many parts of the world,
particularly in children. When energy intake does not match energy needs due
to insufficient dietary intake, excessive intestinal losses, or a combination thereof,
several mechanisms of adaptation come into play. A reduction in voluntary
physical activity is a rapid means to reduce energy output. In children, a reduc-
tion in growth rate is another mechanism to reduce energy needs. However, if
this condition persists in children, low growth weight results in short stature
and low weight-for-age, a condition known as stunting. A chronic energy defi-
cit elicits the mobilization of energy reserves, primarily adipose tissue, which
leads to changes in body weight and body composition over time.
In children, the effects of chronic undernutrition include decreased school
performance, delayed bone age, and an increased susceptibility to infections. In
adults, an abnormally low BMI is associated with decreased work capacity and
limited voluntary physical activity.
ADVERSE EFFECTS OF OVERCONSUMPTION
Two major adverse effects result from the overconsumption of energy:
\u2022 Adaptation to high levels of energy intake: When people are given a diet
providing a fixed, but limited, amount of excess energy, they initially
gain weight. However, over a period of several weeks, their energy ex-
penditure will increase, mostly because of their increased body size. As
such, their body weight will eventually stabilize at a higher weight level.
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
92 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
Reducing energy intake will produce the opposite effect. For most indi-
viduals, it is likely that the main mechanism for maintaining body weight
is controlling food intake rather than adjusting physical activity.
\u2022 Increased risk of chronic disease: A BMI of \u2265 25 kg/m2 is associated with an
increased risk of premature mortality. In addition, as BMI increases be-
yond 25 kg/m2, morbidity risk increases for Type II diabetes, hyperten-
sion, coronary heart disease (CHD), stroke, gallbladder disease, osteoar-
thritis, and some types of cancer. Because some studies suggest that
disease risk begins to rise at lower BMI levels, some investigators have
recommended aiming for a BMI of 22 kg/m2 at the end of adolescence.
This level would allow for some weight gain in mid-life without sur-
passing the 25 kg/m2 threshold.
For the above reasons, energy intakes associated with adverse risks are defined
as those that cause weight gain in individuals with body weights that fall within
the healthy range (BMI of 18.5\u201325 kg/m2) and overweight individuals (BMI of
25\u201330 kg/m2). In the case of obese individuals who need to lose weight
to improve their health, energy intakes that cause adverse risks are those that
are higher than intakes needed to lose weight without causing negative health
consequences.
KEY POINTS FOR ENERGY
3 Energy is required to sustain the body\u2019s various functions,
including respiration, circulation, metabolism, physical work,
and protein synthesis.
3 A person\u2019s energy balance depends on his or her dietary
energy intake and total energy expenditure, which includes the
basal energy expenditure, the thermic effect of food, physical
activity, thermoregulation, and the energy expended in
depositing new tissues and in producing milk.
3 Imbalances between energy intake and expenditure result in
the gain or loss of body components, mainly in the form of fat.
These gains or losses determine changes in body weight.
3 The EER is the average dietary energy intake that is predicted
to maintain energy balance in a healthy adult of a defined age,
gender, weight, height, and a level of physical activity that is
consistent with good health.
3 In children and in pregnant and lactating women, the EER
accounts for the needs associated with growth, deposition of
tissues, and the secretion of milk at rates that are consistent
with good health.
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
PART II: ENERGY 93
3 A person\u2019s body weight is a readily monitored indicator of the
adequacy or inadequacy of habitual energy intake.
3 Numerous factors affect energy expenditure and requirements,
including age, body composition, gender, and ethnicity.
3 There is no RDA for energy because energy intakes above the
EER would be expected to result in weight gain.
3 The UL concept does not apply to energy because any intake
above a person\u2019s energy requirements would lead to
undesirable weight gain.
3 When energy intake is less than energy needs, the body adapts
by mobilizing energy reserves, primarily adipose tissue.
3 In adults, an abnormally low BMI is associated with decreased
work capacity and limited voluntary physical activity.
3 The overconsumption