Download Chapter 14 Summary

Chapter 14 Summary
Life is a continuum that begins with birth and is marked by periods of growth and development. These
changes coincide with stages of the life span that include infancy, childhood, adolescence, adulthood, and
the special life stages of pregnancy and lactation. Changes in body size and composition can influence
nutrient requirements. Growth is an increase in body size, whereas development is the acquisition of
increased complexity of function. Growth occurs when the number (hypertrophy) and/or the size
(hyperplasia) of cells increase. When physical maturity is reached, the rate of cell turnover (cell formation
and breakdown ) is in equilibrium. With increasing age, the rate of new cell formation slows, resulting in
a decline in physiological function, called senescence.
After conception, a zygote undergoes cell division and becomes a blastocyst. Certain cells of the
blastocyst form the fetus, and others join with maternal tissues to form the placenta. The placenta
transfers nutrients, gases, hormones, and other products between the mother and the fetus. By the end of
the embryonic period the basic structures of all major body organs have been formed. Substances and
conditions that disrupt normal growth and development are called teratogens. The fetal period follows
the embryonic period. Babies with a gestational age of 37 weeks or greater are full term, whereas those
with a gestational age less than 37 weeks are preterm. Most preterm infants are born with low birth
weight (LBW), which can also be caused by intrauterine growth retardation (IUGR). Babies who
experience IUGR are small for gestational age (SGA). Gestational age is determined by counting the
number of weeks between the first day of a woman’s last normal menstrual period and birth. Infants born
with a birth weight between the 10th and 90th percentiles for gestational age are classified as appropriate
for gestational age (AGA), whereas those with a birth weight above the 90th percentile are classified as
large for gestational age (LGA).
Adequate weight gain, a healthy diet, and smoking can influence birth weight and gestation length.
Energy requirements increase during pregnancy, as do those for macro- and most micronutrients. Energy
is needed during pregnancy to support the growth of the fetus, placenta, and maternal tissues. Women
are advised to increase their energy intake above nonpregnancy Estimated Energy Requirements by an
additional 348 kcal/day and 452 kcal/day during the second and third trimesters of pregnancy,
respectively. Carbohydrates should remain the primary energy source throughout pregnancy. Additional
protein (25 g/day) is needed for the formation of fetal and maternal tissues. Dietary fat should provide 20
to 35% of total calories. Although extra calcium is needed for the fetus to grow and develop, changes in
maternal physiology can accommodate these needs without increasing dietary intake. Iron is needed for
forming hemoglobin and for the growth and development of the fetus and the placenta. The RDA for iron
during pregnancy increases to 27 mg/day. Folate plays an important role in cell division and is critical to
the development of the nervous system. Women with poor folate status are at increased risk of having a
baby born with a neural tube defect. The RDA for folate during pregnancy is 600 g/day. Smoking during
pregnancy increases the risk of having a preterm and/or LBW baby.
Physiological changes during pregnancy prepare the breasts for producing milk. Milk production takes
place in mammary secretory cells and is regulated in part by the hormones prolactin and oxytocin.
Nursing stimulates the hypothalamus, which in turn signals release of prolactin and oxytocin from the
pituitary gland. Prolactin stimulates milk synthesis, and oxytocin is needed for the release of milk out of
the alveoli and into the ducts—a process called milk let-down. To maintain lactation, it is important for
the mother to breastfeed her infant regularly. Like pregnancy, lactation requires additional nutrients and
energy. Breastfeeding is the preferred method of nourishing infants, because human milk has many
nutritional and immunological benefits. Breastfeeding also has health benefits for women.
Infants grow and development rapidly during the first year of life. By 6 months of age, weight has
doubled, and by 12 months, it has tripled. The American Academy of Pediatrics recommends exclusively
breastfeeding during the first six months of life. Although human milk is recommended, infant formula is
an alternative derived either from cow milk (cow-based formula) or soybeans (soy-based formula). In
communities without fluoridated water, fluoride supplements may be necessary after 6 months of age.
Iron supplements are recommended for infants who are exclusively breastfed during the second six
months of life. Vitamin D drops are recommended for breastfed infants after 2 months of age. Human
milk and/or infant formula should be the primary source of nutrients and energy throughout the first
year of life. However, nonmilk complementary foods can begin sometime between 4 to 6 months of age,
depending on an infant’s readiness. The first solid food often fed to infants is iron-fortified cereal. Older
infants should be given a wider variety of foods, although they should be chosen carefully to pose
minimal risk for choking.
Childhood is a stage of the life span characterized by growth and development. Growth is monitored
using sex-specific growth charts. Children between the 85th and 95th percentile based on BMI-for-age are
considered at risk for being overweight, and those at or above the 95th percentile are considered
overweight. Children below the 5th percentile are considered underweight. Excess weight that persists
throughout childhood is of concern and increases the risk for developing weight-related health problems.
Developmental changes can make feeding children challenging for parents. Parents should make
mealtime pleasant and provide age-appropriate, healthy food choices. A diet that provides adequate
nutrients and energy is important throughout childhood. Nutrients needed for bone health (such as
calcium) and to support growth (such as iron) are particularly important. The Dietary Guidelines for
Americans 2005 stress the importance of providing children with nutrient-dense foods and regular
physical activity.
Hormonal changes begin the transformation from childhood into adolescence, causing changes in height,
weight, and body composition. Adolescence is also the beginning of reproductive maturity. The timing of
these changes varies, and therefore adolescents of the same age can differ in terms of physical maturation
and nutritional requirements. Linear growth is completed at the end of the adolescent growth spurt,
although bone mass continues to increase into early adulthood. Thus it is important that adolescents have
adequate intakes of nutrients related to bone health. Changes in body composition during adolescence
are different for males and females. Overall, males experience an increase in lean mass relative to a
decrease in body fat, whereas females decrease in lean mass relative to body fat. Although increased
body fat in females is normal and healthy, it can contribute to weight dissatisfaction. The rapid growth
and development associated with adolescence increases the body’s need for certain nutrients and energy.
Estimated Energy Requirements (EERs) take into account both energy expenditure and additional energy
needed for growth.
The risk of developing diet-related chronic disease increases with age. Adults who remain physically
active and maintain a nutritious diet tend to live longer and have fewer health problems. Physiological
changes associated with aging can also affect nutritional status. As individuals grow older, they
experience a relative loss of lean mass and increase in fat mass. For this reason, energy requirements
decrease. The loss of muscle mass can make older people less steady and can increase the risk for injury.
Exercise helps maintain a healthy weight, decreases fat mass, slows age-related bone loss, strengthens
muscles, and improves coordination. Because age-related bone loss can make bones fragile, it is
important for older adults to have adequate intakes of calcium, vitamin D, phosphorus, and magnesium.
Many factors can contribute to inadequate food intake in older adults, including poor oral health, altered
taste, and decreased ability to smell. Older adults may not be able to readily detect thirst and are at
increased risk for dehydration. Age-related changes in the gastrointestinal tract can also affect nutritional
status. A decrease in production of gastric secretions can impair absorption of iron, calcium, biotin, folate,
vitamin B12, and zinc. Of particular concern is the risk of pernicious anemia, which is especially a problem
in this group. Services that provide food to older adults include congregate meal programs, meal delivery
programs, and Food Stamps.