Livro DRI 2006 (Micronutrientes)

Livro DRI 2006 (Micronutrientes)


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Changing one\u2019s usual activity level can have a major impact on total energy
expenditure and energy balance. The ultimate indicator of this energy balance
is body weight, as seen through its maintenance or change.
Energy intake and the energy expenditure of physical activity are control-
lable variables that impact energy balance, in contrast to other uncontrollable
variables that include age, height, and gender. During exercise, energy expendi-
ture can increase far beyond resting rates, and the increased energy expenditure
induced by a workout can persist for hours, if not a day or longer. Furthermore,
exercise does not necessarily boost appetite or intake in direct proportion to
activity-related changes in energy expenditure.
HEALTHFUL EFFECTS OF PHYSICAL ACTIVITY
Observational and experimental studies of humans and animals provide bio-
logically plausible insights into the benefits of regular physical activity on the
delayed progression of several chronic diseases, including cancer, cardiovascu-
lar disease, Type II diabetes, obesity, and skeletal conditions. In addition, acute
or chronic aerobic exercise may be related to favorable changes in anxiety, de-
pression, stress reactivity, mood, self-esteem, and cognitive functioning.
It is difficult to determine a quantifiable recommendation for physical ac-
tivity based on reduced risk of chronic disease. However, meeting the physical
activity recommendation of 60 minutes per day offers additional benefits in
reducing the risk of chronic disease; for example, by favorably altering blood
lipid profiles, changing body composition by decreasing body fat, and increas-
ing muscle mass, or both.
Endurance (Aerobic) Exercise
Traditionally, the types of activities recommended for cardiovascular fitness
are those of a prolonged endurance nature, such as bicycling, hiking, jogging,
and swimming. Because of the energy demands associated with these pro-
longed mild to moderate intensity endurance activities, they have the poten-
tial to decrease body fat mass and preserve fat-free mass, thus changing body
composition.
Resistance Exercise and General Physical Fitness
Although resistance training exercises have not yet been shown to have the
same effects as endurance activities on the risks of chronic disease, their effects
on muscle strength are an indication to include them in exercise prescriptions,
in addition to activities that promote cardiovascular fitness and flexibility. Exer-
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: PHYSICAL ACTIVITY 99
cises that strengthen the muscles, bones, and joints stimulate muscular and
skeletal development in children, as well as assist in balance and locomotion in
the elderly, thereby minimizing the incidence of falls and associated complica-
tions of trauma and bed rest.
EXCESSIVE PHYSICAL ACTIVITY
Excessive physical activity can lead to the following adverse effects:
\u2022 Overuse injuries: Too much or improper physical exercise can cause over-
use injuries to muscles, bones, and joints, as well as injuries caused by
accidents. In addition, pre-existing conditions can be aggravated by the
initiation of a physical activity program. Activity-related injuries are of-
ten avoidable but do occur and need to be resolved in the interest of
long-term general health and short-term physical fitness.
\u2022 Dehydration and hyperthermia: Exercise may cause dehydration, which
can be aggravated by environmental conditions that increase fluid losses,
such as heat, humidity, and lack of wind. People should consume water
before, during (if possible), and after exercise.
\u2022 Hypothermia: Hypothermia can result from water exposure and heat loss
during winter sports. Poor choice of clothing during skiing, accidental
water immersion due to a capsized boat, weather changes, or physical
exhaustion may lead to the inability to generate adequate body heat to
maintain core body temperature, which can lead to death, even when
temperatures are above freezing.
\u2022 Cardiac events: Although regular physical activity promotes cardiovas-
cular fitness, heavy physical exertion can trigger the development of
arrhythmias or myocardial infarctions or, in some instances, can lead to
sudden death.
\u2022 Female athlete triad: Athletic women who undereat or overtrain can de-
velop a condition, or cluster of conditions, called the \u201cfemale athlete
triad.\u201d In this triad, disordered eating and chronic energy deficits can
lead to loss of menses, osteopenia, and premature osteoporosis, increas-
ing the risk of hip, spine, and forearm fractures.
Prevention of Adverse Effects
Previously sedentary people are advised to begin a new activity routine with
caution. The following people should seek medical evaluation, as well as clini-
cal exercise testing, clearance, and advice prior to starting an exercise program:
men over age 40 years, women over age 50 years, people with pre-existing
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
100 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
medical conditions, and people with known or suspected risk factors or symp-
toms of cardiovascular and other chronic diseases (physical inactivity being a
risk factor). For those with cardiovascular risk or orthopedic problems, physi-
cal activity should be undertaken with professional supervision. For all indi-
viduals, easy exercise should be performed regularly before more vigorous ac-
tivities are conducted.
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: PHYSICAL ACTIVITY 101
KEY POINTS FOR PHYSICAL ACTIVITY
3 Lack of physical activity and obesity are now recognized risk
factors for several chronic diseases.
3 Observational and experimental studies of humans and animals
provide biologically plausible insights into the benefits of
regular physical activity on the delayed progression of several
chronic diseases, including cancer, cardiovascular disease,
Type II diabetes, obesity, and skeletal conditions.
3 Acute or chronic aerobic exercise may be related to favorable
changes in anxiety, depression, stress reactivity, mood, self-
esteem, and cognitive functioning.
3 Changing one\u2019s usual activity level can have a major impact on
total energy expenditure and energy balance.
3 In addition to activities that characterize a sedentary lifestyle,
an average of 60 minutes per day of moderate-intensity
physical activities (e.g., brisk walking or jogging at 3\u20134 mph) or
shorter periods of more vigorous exertion (e.g., jogging for 30
minutes at 5.5 mph) is the amount of physical activity
recommended for normal-weight adults. For children, the
physical activity recommendation is also an average of 60
minutes of moderate-intensity daily activity.
3 More than 60 percent of American adults are not regularly
physically active and 25 percent are not active at all. Similar
trends are seen in children.
3 Excessive physical activity can lead to overuse injuries,
dehydration and hyperthermia, hypothermia, cardiac events,
and female athlete triad (loss of menses, osteopenia, and
premature osteoporosis).
3 Previously sedentary people are advised to begin a new activity
routine with caution to prevent adverse effects.
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
TABLE 1 Dietary Reference Intakes for Dietary
Carbohydrates: Sugars and Starches by Life Stage Group
DRI values (g/day)
EARa RDAb AIc