 |  Perspectives in Nutrition, 5/e Gordon M. Wardlaw,
Ohio State University
Margaret W. Kessel,
Ohio State University
Energy Balance and Weight Control
Chapter 13 Summary- Energy balance is energy intake minus energy output. Negative energy
balance occurs when energy output surpasses energy intake, resulting in weight
loss. Positive energy balance occurs when energy intake is greater than energy
output. The result is weight gain.
- Groups of cells in the hypothalamus and other regions in the brain
affect hunger, the primarily internal desire to find and eat food. These cells
monitor nutrients and other substances in the blood and read low amounts as
a signal to promote feeding.
- A variety of external (appetite-related) forces affect satiety. Hunger
cues combine with appetite cues, such as easy availability of food, to promote
feeding.
- In North America, the major determinants of food intake are probably
appetite-driven forces because food is so readily available. The physiological
influences affecting food consumption are often suppressed or ignored.
- Basal metabolism, the thermic effect of food, physical activity,
and nonexercise activity thermogenesis account for total energy use by the body.
Basal metabolism, which represents the minimum energy expenditure needed to
keep the resting, awake body alive, is primarily affected by lean body mass,
surface area, and thyroid hormone concentrations. Physical activity represents
energy use above that expended at rest. The thermic effect of food represents
the increase in metabolism to facilitate the digesting, absorbing, and processing
of nutrients recently consumed. Nonexercise activity thermogenesis is heat production
caused by overfeeding and other stimuli. About 70 to 80% of energy use is accounted
for by basal metabolism and the thermic effect of food in a primarily sedentary
person.
- Energy use by the body can be measured directly from heat output
or indirectly from oxygen uptake, carbon dioxide output, or both. Energy use
by the body can be estimated using formulas based on various combinations of
body height and weight with degree of physical activity and age.
- A person of healthy weight shows good health and performs daily activities
without weight-related problems. A body mass index (weight [in kilograms] ÷height2 [in meters]) of 18.5 to 25 is one measure of healthy weight, although
weight in excess of this value may not lead to ill health. This suggests that
healthy weight is best determined in conjunction with a thorough health evaluation
by a physician.
- Obesity is usually defined as total body fat percentage over 25%
in men and about 35% in women. A body mass index over 30 also represents obesity.
- Fat distribution partially determines health risks from obesity.
Upper-body fat-storage distribution (waist circumference > 40 inches in men
and > 35 inches in women) suggests higher risks of hypertension, cardiovascular
disease, and type 2 diabetes associated with obesity than does lower-body fat
distribution.
- Genetic factors influence the tendency toward obesity. Basal metabolism
and body-fat distribution both have genetic links. How a person is raised (or
nurtured) also influences the tendency toward obesity because family members
often develop similar eating habits and activity patterns. Obesity can be viewed
as nurture allowing nature to be expressed.
- Those in search of a treatment for obesity should remember these
five points: (1) A focus on healthy lifestyle rather than weight loss per se
is more appropriate for many potential and current dieters; (2) the body resists
weight loss; (3) the emphasis should be on preventing obesity because curing
the disorder is very difficult; (4) weight loss should represent mostly a loss
of fat storage and not primarily the loss of muscle and other lean tissues;
and (5) rapid weight loss and quick regain can be especially harmful to emotional
health.
- A sound weight-loss program meets the dieter's nutritional needs
by emphasizing a wide variety of low-fat and nonfat food choices from the Food
Guide Pyramid; it adapts to the dieter's habits, consists of readily obtainable
foods, strives to change poor eating habits, stresses regular physical activity,
and stipulates the participation of a physician if weight is to be lost rapidly
or if the person is over 40 (men) or 50 (women) years of age and plans to perform
substantially greater physical activity than usual.
- A pound of fat contains about 3500 kcal. A pound of adipose tissue--the
fat itself plus lean support tissue--lost or gained represents approximately
2700 kcal. Thus, if energy output exceeds energy intake by about 500 kcal/day,
a pound of fat storage can be lost per week. Decreasing the intake of high-fat
foods is probably the best way to obtain this energy deficit, along with increasing
physical activity.
- Physical activity as part of a weight-loss program should be focused
on duration rather than intensity. Ideally, vigorous activity should be part
of each day.
- Behavior modification is a vital part of a weight-loss program because
the dieter may have many habits that encourage overeating and thus discourage
weight maintenance. Specific behavior-modification techniques, such as stimulus
control and self-monitoring, can be used to help change problem behavior.
- Medications to blunt appetite, such as phenteramine [Fastin] and
sibutramine (Meridia), can aid weight-reduction strategies. Orlistat (Xenical)
reduces fat absorption in a meal when taken with the meal. Use is reserved for
those who are obese or have or weight-related problems, and they must be administered
under strict physician supervision.
- The treatment of severe obesity may include surgery to reduce stomach
volume to approximately 30 ml or very-low-calorie diets containing 400 to 800
kcal per day. Both these measures should be reserved for people who have failed
at more conservative approaches to weight loss. They require close medical supervision.
- Underweight can be caused by a variety of factors, such as excessive
physical activity and genetic background. Sometimes being underweight requires
medical intervention. A physician should be consulted first to rule out ongoing
disease. The underweight person may need to increase portion sizes and learn
to like energy-dense foods. In addition, encouraging a regular meal and snack
schedule aids in weight gain and maintenance. A physically active person can
reduce excessive activity and substitute some resistance exercise (weight training).
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2002 McGraw-Hill Higher Education