728
UNIT FIVE
For all ages, weight gain occurs when energy in
exceeds energy out, and weight loss happens when energy
out exceeds energy in. Age f ±ty seems to be a key point in
energy balance. For most people, energy balance is positive,
and weight is maintained be±ore this age, but a±terwards,
weight may creep up. However, being aware o± a decrease in
activity, and curbing ±ood consumption accordingly, enables
many people over the age o± f
±ty to maintain their weight.
Changing nutrition with age o±ten refl ects e±±ects o± medi-
cal conditions, many o± which are more common among older
people, and social and economic circumstances. Medications
can dampen appetite directly through side e±±ects such as nau-
sea or altered taste perception or a±±ect a person’s mood in a
way that prevents eating. Poverty may take a greater nutri-
tional toll on older people who either cannot get out to obtain
±ood or who give whatever is available to younger people.
Medical conditions that a±±ect the ability to obtain ade-
quate nutrition include depression, tooth decay and peri-
odontal disease, diabetes mellitus, lactose intolerance, and
alcoholism. These conditions may lead to def ciencies that
are not immediately obvious. Vitamin A def
ciency, ±or exam-
ple, may take months or years to become noticeable because
the liver stores this ±at-soluble vitamin. Calcium depletion
may not produce symptoms, even as the mineral is taken
±rom bones. The earliest symptom o± malnutrition, ±atigue,
may easily be attributed to other conditions or ignored.
Evidence ±or vitamin D def ciency related to sun avoid-
ance has a long history. The link between lack o± sunlight
and development o± rickets was noted in 1822, and a century
later, researchers realized that sun exposure helps reverse
the disease in children. Other evidence comes ±rom diverse
sources, such as women who wear veils and naval personnel
serving three-month tours o± duty on submarines.
It is important to obtain a good balance o± nutrients and
enough energy throughout li±e. Many studies link caloric
restriction to increased longevity in species such as mice and
±ruit fl ies. However, these observations cannot be extrapo-
lated to humans because the experimental laboratory animals
were kept extremely healthy. Human starvation is usually
the consequence o± many other problems and is more likely
to lead to malnutrition than increased longevity.
PRACTICE
82
List factors that aF
ect nutrient acquisition.
83
Describe changes in BMR throughout life.
Bulimia
A person su±±ering ±rom
bulimia
(bu-lim
e-ah) is o±ten o±
normal weight. She eats whatever she wants, o±ten in huge
amounts, but she then rids her body o± the thousands o±
extra calories by vomiting, taking laxatives, or exercising
±rantically. For an estimated one in f
ve college students, the
majority o± them ±emale, “bingeing and purging” appears to
be a way o± coping with stress.
Sometimes a dentist is the f
rst to spot bulimia by observ-
ing a patient with teeth decayed ±rom ±requent vomiting. The
backs o± her hands may bear telltale scratches ±rom e±±orts to
induce vomiting. Her throat is raw and her esophageal lining
ulcerated ±rom the stomach acid ±orced ±orward by vomiting.
The binge and purge cycle is hard to break, even with psy-
chotherapy and nutritional counseling.
Underweight and overweight are societal problems complexly con-
nected to economics. A phenomenon called a “dual-burden household”
affects nations that were recently considered to be developing, but
where the gross national product is on the rise. The problem is that in
poor countries, the poorest people lack food and toil at physically taxing
jobs, and so are severely underweight. But as economic resources come
to a country, poor people who ±
nd jobs in newly urbanized areas begin
to eat the cheapest food, of low nutritional quality, and sometimes too
much of it. O²
ce jobs rather than working in ±
elds, and wider availabil-
ity of television, promote a sedentary lifestyle. The result: weight gain. At
the same time, underweight in children under ±
ve is increasing in urban
areas of countries whose socioeconomic status is changing, according
to the World Bank. This may re³
ect lack of home-grown foods, previ-
ously a major dietary staple, as both parents work in nonagricultural
jobs. One researcher calls the coexistence of underweight and over-
weight in transitional countries “a nutritional paradox.”
PRACTICE
78
What is primary malnutrition? Secondary malnutrition?
79
What happens to the body during starvation?
80
How do marasmus and kwashiorkor diF
er?
81
How do anorexia nervosa and bulimia diF
er?
18.9
LIFE-SPAN CHANGES
Dietary requirements remain generally the same throughout
li±e, but the ability to acquire those nutrients may change
drastically. The basal metabolic rate (BMR) changes with
age. It rises ±rom birth to about age f
ve and then declines
until adolescence, when it peaks again. During adulthood,
the BMR drops in parallel to decreasing activity levels and
shrinking muscle mass. In women, it may spike during
pregnancy and breast±eeding, when caloric requirements
likewise increase.
Table 18.12
shows changes in energy
requirements ±or adults who are healthy and engage in reg-
ular, light exercise.
TABLE
18.12
|
Energy Requirements Decline
with Age
CAL/DAY
Age
Female
Male
23–50
2,000
2,700
51–74
1,800
2,400
75+
1,600
2,050
previous page 758 David Shier Hole's Human Anatomy and Physiology 2010 read online next page 760 David Shier Hole's Human Anatomy and Physiology 2010 read online Home Toggle text on/off