Transcript nieman6e_ch13

Chapter 13
Obesity
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How can an individual know if they are overweight/overfat?
There is a wide range of options, and a large industry has
developed in body composition analysis.
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How To Estimate Obesity
Obesity threshold weights
for given heights
Obesity can be estimated by using
a mathematical formula called the
body mass index (BMI) - weight in
kilograms divided by height in
meters squared (BMI = kg/m2).
A BMI of 18.5 to 24.9 is considered a
"normal" weight.
A BMI of 25 to 29.9 is considered
overweight
A BMI of 30 or above is considered
obese.
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Obesity/Overweight Prevalence
Obesity affects about 3 in 10 adults (compared to Healthy
People 2010 goal of 15%), with the highest rates among
the poor and minority groups (Figure 13.2).
65% overweight/obese (Figure 13.3).
Compared to 1960, average adult now weighs 24 pounds
more (males = 190 pounds, 69 inches, BMI 28; females =
163 pounds, 64 inches, BMI 28) and the average teenager
15 pounds more.
Figure 13.4 shows dramatic increase in obesity prevalence
on a state-by-state basis.
Among children and adolescents, 16% is rated as
overweight, up substantially from the 1960s (Figure 13.5)
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Figure 13.2
Healthy People 2010 Goal
All adults
30.4
All males
27.5
33.2
All females
White males
28
White females
30.7
27.8
Mexican-American males
Mexican-American females
38
Black males
27.8
48.8
Black females
0
10
20
30
40
50
Prevalence of Obesity (BMI 30+)
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Figure 13.3
Obese
Overweight or obese
Healthy weight
32.9
1999-02
65.2
31.1
41.7
1988-94
56
23.3
49.6
47.4
1976-80
15.1
48.8
47.7
1971-74
14.6
1960-62
44.8
51.2
13.3
0
10
20
30
40
50
60
Percent of Population (20 years of age and older)
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Obesity Trends* Among U.S. Adults
BRFSS, 1991, 1996, 2004
(*BMI 30, or about 30 lbs overweight for 5’4” person)
1991
1996
2004
No Data
<10%
10%–14%
15%–19%
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20%–24%
≥25%
Figure 13.5
12-19 yrs old
6-11 yrs old
16
16
1999-02
11.4
10.5
1988-94
6.5
1976-80
5
4
1971-74
6.1
4.2
4.6
1963-70
0
5
10
Prevalence of overweight
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15
20
Health Risks of Obesity
A psychological burden
Increased high blood pressure (Fig 13.6)
Dyslipidemia (high cholesterol, triglycerides, LDL-C, low
HDL-C (Fig 13.7)
Increased risk of gallstones (Fig 13.8)
Increased osteoarthritis (Fig 13.9)
Increased diabetes (type 2) (Chapter 12, Figs 12.6-12.8)
Increased cancer (colon, rectum, prostate, pancreas, liver,
kidney, breast, uterus, ovaries, gallbladder, bile ducts)
(Chapter 11, Figs 11.6, 11.19, 11.24)
Increased mortality and early death (Figs 13.10, 13.11)
Increased heart disease and stroke (Figs 13.12, 13.13)
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Fig. 13.14
Health risks
are worst for
androids
(waist circumference
>35 inches in women,
and >40 inches in men)
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What Factors Best Explain The
Obesity Epidemic In America?
3.
2.
1.
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Genetic and Parental Influences
Dr. Mayer, 1965: 80% of offspring of 2 obese parents become obese,
40% with one, and 14% with none. Parental obesity predicts obesity
in their offspring, especially when present during the first 10 years of
life (Fig 13.18). More than 80% of obese adolescents remain obese
as adults (Fig 13.20).
Twin studies show that identical twins reared apart have BMIs as
close as when reared together.
Adults adopted before age 1 have BMIs most similar to biologic
parents.
Inheritance accounts for 25% of variance in fatness, with
lifestyle/environment 45%. See figure 13.19). Subsequent research
suggests 25-40% of variance in obesity has genetic basis.
Some people are obesity prone because of their genes and must
exercise more and eat less than others to achieve desirable weight.
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Genetics? Parental influences? One-third of
preschoolers become obese as adults, but 80% of
teenagers end up obese as adults (Fig 13.20).
Prev Med 22:167-177, 1993.
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High Energy Intake
Do obese people eat more than the nonobese?
Older studies used 3-7 day food records, and
data suggested energy intake was similar
between obese and nonobese.
However, obese people tend to underestimate
intake by 20-50% (Figure 13.21).
Use of respiratory chambers and doubly
labeled water show that obese people both
expend and ingest more energy (Figure
13.22).
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Most obese people are in self-denial. This study showed that
obese subjects underestimate food intake by 50% and
overestimate physical activity by 33% (Fig.13.21).
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High Energy Intake
When dietary fat intake is high, most adults
and children tend to gain weight easily and
quickly.
Obese compared to lean people tend to
choose high-fat and energy-rich foods more
often.
High fat foods are more palatable,
prompting people to take in more energy
(Figs 13.23 to 13.25).
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Low Energy Expenditure
Humans expend energy in 3 ways (Figure 13.26).
The resting metabolic rate is directly related to
body weight (high in the obese, lower in the lean),
and parallels changes in weight (Table 13.1, Fig
13.27).
Regular physical activity is related to a reduced risk
of body weight gain (Figs 13.28, 13.29).
Physical activity is significantly lower in obese
people (Fig 13.30, 13.31; Table 13.2).
The thermic effect of food (10%) is slightly lower
in the obese (Figs 13.32, 13.33).
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Daily Energy Expenditure
Fig. 13.26 The largest number of calories expended by most
people (except for athletes during heavy training) is from the
resting metabolic rate (RMR). Am J Clin Nutr 55:242S-s45S, 1992.
Activity
23%
RMR
67%
TEF
10%
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Resting Metabolic Rate (RMR)
Description
The basal metabolic rate
(BMR) represents the energy
needed to support the basic
cost of living, including the
metabolic activities of cells
and tissues, blood circulation,
respiration, and
gastrointestinal and kidney
functions.
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Energy Expenditure and Body Mass Change
Fig. 13.27 The resting metabolic rate is directly related to body
weight (higher in the obese, lower in the lean), and parallels
changes in weight. N Engl J Med 332:621-628, 1995
-300
10% weight loss
-25
Back to initial weight
500
10% weight gain
-400
-200
0
200
400
Energy Expenditure Change (kcal/day)
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600
Table 13.1 RMR Estimation Through Equations
BMR prediction equations have been developed using
easily and accurately measurable variables such as age,
height, and body weight.
The Food and Nutrition Board of the Institute of Medicine
recently developed these equations for estimating BMR in
adults:
Men: BMR (kcal/day) = 293 - (3.8 x age) + (456.4 x height) +
(10.12 x weight)
Women: BMR (kcal/day) = 247 - (2.67 x age) + (401.5 x
height) + (8.6 x weight)
– [Age is in years, height is in meters, and weight is in kilograms].
Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids,
Cholesterol, Protein, and Amino Acids (Macronutrients). Washington, D.C.: The National Academies Press, 2002.
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Equation Example
40 yr old woman, 65 inches, 140 pounds
Women: 65 inches x 0.0254 = 1.65 meters
140 pounds x 0.4536 = 63.5 kg
BMR (kcal/day) = 247 - (2.67 x age) + (401.5 x height)
+ (8.6 x weight)
BMR (kcal/day) = 247 - (2.67 x 40 yr) + (401.5 x 1.65
m) + (8.6 x 63.5 kg) = 1,349
Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol,
Protein, and Amino Acids (Macronutrients). Washington, D.C.: The National Academies Press, 2002.
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Physical activity decreases in direct relationship to
the degree of obesity (Fig. 13.31).
Non-RMR Energy Expenditure
(kcal/kg/day)
Body Fatness and Energy Expenditure In 300 Subjects
(Doubly Labeled Water Method)
50
45
40
35
30
25
20
15
10
5
0
47.5
38
28.5
19
9.5
Lean
Am J Clin Nutr 60:676-681, 1994
Normal
Above Desired
Obese
Body Fat Classification
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Very Obese
Figure 13.32
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Treatment of Obesity Is Challenging
Four in 10 U.S. adults at any given time are trying to lose
weight (Fig. 13.34).
Among adults trying to lose weight, only one in five follow
2 key recommendations: eat fewer calories and increase
physical activity.
Many obese people will not stay in treatment, and of those
who do, most will not achieve ideal weight. Of those who
lose weight, most will regain it (Fig. 13.35).
Regular exercise is a marker of long-term success in
maintaining weight loss (Fig. 13.36, Box 13.2).
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Figure 13.35
Maintenance of Weight Loss Over 5 Years After Treatment
End of Therapy
1 year later
Weight Loss/Gain (Pounds)
10
5 years later
6
6
2
5
0
-5
-10
-10
-15
-15
-20
-25
-30
-23
-29
-29
-37
-35
-40
VLCD Alone
Behavior Therapy
Type of Weight-Loss Program
Int J Obesity 13(suppl 2):39-49, 1989.
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Both
Conservative Treatment
Guidelines
Obesity should be treated as a chronic condition,
not an acute illness.
Incorporate change in diet, increase in physical
activity, and change in behavior.
Aim for about 0.5-2 pounds of weight loss a week.
Each pound of fat = 3,500 calories.
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How to Lose Weight: The NHLBI Obesity
Education Initiative (Box 13.3)
In 1998, the first federal guidelines for the treatment of
overweight and obesity in adults were released by the
National Heart, Lung, and Blood Institute (NHLBI) as a
part of their nationwide Obesity Education Initiative.
Key diet recommendations from this initiative include the
following:
The initial goal of a weight loss regimen should be to reduce
body weight by about 10%. With success, further weight loss
can be attempted, if needed.
Weight loss should be about 1 to 2 pounds per week for a period
of 6 months, with additional plans based on the amount of
weight loss. Seek to create a deficit of 500 to 1,000 calories per
day through a combination of decreased caloric intake and
increased physical activity.
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How to Lose Weight: The NHLBI Obesity
Education Initiative (Box 13.3) (Cont.)
Reducing dietary fat intake is a practical way to reduce calories.
But reducing dietary fat alone without reducing calories is not
sufficient for weight loss.
Each pound of body fat represents about 3,500 calories. To follow
the NHLBI for weight loss, one must expend 500 to 1000 calories
more than the amount taken in through the diet. This can be
accomplished by increasing energy expenditure 200-400 calories a
day through physical activity, and reducing dietary fat intake by
300-600 calories. Each tablespoon of fat represents about 100
calories, so an emphasis on low-fat dairy products and lean meats,
and a low intake of visible fats is the easiest way to reduce caloric
intake without reducing the volume of food eaten.
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How to Lose Weight: The NHLBI Obesity
Education Initiative (Box 13.3) (Cont.)
The NHLBI recommends this diet for weight loss:
Eat 500-1,000 calories a day below usual intake.
Keep total dietary fat intake below 30% of calories,
and carbohydrate at 55% or more of total calories.
Emphasize a heart-healthy diet by keeping saturated
fats under 10% of total calories, cholesterol under 300
mg per day, and sodium less than 2,400 mg per day.
Choose foods high in dietary fiber (20-30 grams per
day).
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Gastric Reduction Surgery
The NHLBI Obesity Education Initiative
promotes weight loss surgery is an option for
weight reduction in patients with clinically severe
obesity, defined as a BMI≥40, or a BMI≥35 with
comorbid conditions. (See Box 13.5).
Weight loss surgery should be reserved for
clinically severe obese patients in whom other
methods of treatment have failed. See Figure
13.37 for surgery options.
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Weight Loss Drugs
The NHLBI Obesity Education Initiative promotes FDA-approved
weight loss drugs for long-term use as an adjunct to diet and
physical activity for patients with a BMI≥30 and without
concomitant obesity-related risk factors or disease. (See Box 13.5).
Drug therapy may also be useful for patients with a BMI≥27 who
also have concomitant obesity-related risk factors or diseases.
In general, drugs should be used only as part of a comprehensive
program that includes behavior therapy, diet, and physical activity.
Appropriate monitoring for side effects must be continued while
drugs are part of the regimen. Since obesity is a chronic disease,
the short-term use of drugs is not helpful. The health professional
should include drugs only in the context of a long-term treatment
strategy.
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Very Low Calorie Diets
The VLCD provides 400-800 Calories/day; long-term
success is poor (see Figure 13.39).
The NHLBI recommends that VLDCs not be used routinely
for weight-loss therapy:
Energy deficits are too great.
Nutritional inadequacies will occur without supplements.
Moderate energy restriction is just as effective over the long-term.
Rapid weight reduction does not promote gradual change in eating
behavior.
Linked to increased risk of gallstones.
Require special monitoring.
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Misconceptions Regarding the Role
of Exercise In Weight Loss (Box 13.9)
Accelerates weight loss significantly when combined
with a reducing diet (Figs 13.40 to 13.43).
Causes the RMR to stay elevated for a long time after the
bout, burning extra calories (Figs 13.44, 13.45).
Counters the diet-induced decrease in RMR (Figs 13.46,
13.47, 13.48).
Counters the diet-induced decrease in fat- free mass (Fig
13.46, 13.49, 13.50).
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Misconception #1: Aerobic Exercise Accelerates
Weight Loss Significantly When Combined With A
Reducing Diet
Some obese people have been led to believe that if they start brisk
walking 2-3 miles/day (or workout for 30-45 min/day) significant
amounts of body weight will be lost quickly. This is not true.
Body Weight Changes Over 12-Weeks With Diet And/Or Exercise
0
Fig. 13.40
Weight Loss (Pounds)
-2
-1.8
-2.2
-4
-6
-8
-10
-12
-14
-17.8
-17.2
-16
-18
Controls
Walking
Diet
Diet and Walking
Group Status (Diet 1,300 kcal/day); Exercise (5-45 min walk/wk)
Int J Sports Nutr 8:213-222, 1998.
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Why? The net energy expenditure of exercise is
small (only about 135 kcal per 3-mile walk). To be
accurate, the RMR and potential informal activity
calories must be subtracted out.
Fig. 13.43
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Misconception #2: Exercise Causes the Resting Metabolic Rate to Stay
Elevated for a Long Time after the Bout, Burning Extra Calories
The truth is that the energy expended
after aerobic exercise is small unless a
great amount of high intensity exercise
is engaged in.
Moderate intensity exercise for 30 min
increases the RMR for only 20-30 min,
burning 10-20 extra calories.
High intensity exercise for 30 min
increases the RMR for 35-45 min, burning
15-30 extra calories.
Thus when the obese individual walks for
20-30 min, about 10 extra calories will be
burned afterwards, hardly enough to be
meaningful.
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RMR
100
Fat Mass
90
75
80
Percentage
Fat-Free Mass
60
50
40
50
25
20
10
0
-20
-40
-5
-15
1200-1500
400-800
-25
Fasting
Energy Intake (Kcal/day)
Fig. 13.46 During caloric restriction (dieting), the resting metabolic rate
drops 5-30%, and the fat-free mass drops 10-50% (with degree of
decrease depending on the severity of the energy decrease).
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Misconception #3: Exercise counters the diet-induced decrease in RMR.
Most studies have found that exercise during dieting does not
counter the decrease in RMR and fat-free mass.
65 obese, 8 wk, formula diet at 70% RMR; aerobics 3/wk,
leg/arm cycling; weights 3x/wk, 3x6, 8 stations.
Am J Clin Nutr 66:557-563, 1997.
0
Fig.
13.47
Change in RMR (kcal)
-20
-40
Diet Alone
Aerobics & Diet
Weights & Diet
-60
-80
-100
-88
-120
-127
-140
-160
-148
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Percent Decrease in RMR
0
-2
Diet Alone
Weights & Diet
-4
-6
-8
-9
-10
-10.3
-10.6
-10.3
-12
Fig. 13.48 90 day study of 69 obese females, all on 520 kcal/day
formula. Aerobics = 4 d/wk, 20 min progressing to 60 min/session;
weights = 4 d/wk, 2-3 sets, 6-8 reps.
Am J Clin Nutr 54:56-61, 1991.
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Practical Conclusions
To sum up, individuals adopting a moderate exercise program to
lose weight should not count on a revved up metabolism to burn a
significant amount of extra calories beyond that linked to the
exercise itself.
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2005 USDA
Dietary Guidelines
■ To reduce the risk of chronic disease in
adulthood: Engage in at least 30 min of
moderate-intensity physical activity, above
usual activity, at work or home on most days
of the week.
■ To help manage body weight and prevent
gradual, unhealthy body weight gain in
adulthood: Engage in approximately 60 min
of moderate- to vigorous-intensity activity on
most days while not exceeding caloric intake
requirements.
■ To sustain weight loss in adulthood:
Participate in at least 60-90 min of daily
moderate-intensity physical activity while
not exceeding caloric intake requirements.
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The Power Behind Weight Loss?
Eating less has the biggest impact on weight loss.
Exercise helps, but must exceed 60 minutes a day to be
meaningful (more than most obese individuals are willing
to endure) (Jeffery et al. Am J Clin Nutr 2003;78:684-689).
Exercise is more important in improving the health of the
obese individual during weight loss than in accelerating
weight loss.
Thus in the “battle of the bulge,” jab with exercise and
deliver the knock-out blow with diet.
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Box 13.10 So Then Why Exercise When
Trying to Lose Weight?
Improves heart lung fitness (which tends to be low in
obese individuals).
Improves overall health, and decreases the risk of obesityrelated diseases such as heart disease, stroke, cancer, and
hypertension.
Improves the blood lipid profile, with an increase in HDLC and a decrease in triglycerides.
Improves psychological state, especially increased general
well-being and vigor and decreased anxiety and
depression.
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The Surgeon General’s Call To Action To Prevent and
Decrease Overweight and Obesity
The Nation must take action to assist Americans in balancing
healthful eating with regular physical activity. Individuals and
groups across all settings must work in concert to:
Ensure daily, quality physical education in all school grades.
Reduce time spent watching television and in other similar sedentary
behaviors.
Build physical activity into regular routines and playtime for children and
their families.
Create more opportunities for physical activity at worksites.
Make community facilities available and accessible for physical activity for
all people.
Promote healthier food choices, including at least 5 servings of fruits and
vegetables each day, and reasonable portion sizes at home, in schools, at
worksites, and in communities.
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Exercise Prescription Guidelines
Initially, moderate levels of physical activity for 30 to 45 minutes, 3 to 5 days per
week, should be encouraged.
Starting a physical activity regimen may require supervision for some obese
people. The need to avoid injury during physical activity is a high priority.
Extremely obese persons may need to start with simple exercises that can be
intensified gradually. For most obese patients, physical activity should be initiated
slowly, and the intensity should be increased gradually.
Initial activities may be increasing small tasks of daily living. With time, the patient
may engage in more strenuous activities.
A regimen of daily walking is an attractive form of physical activity for many
people, particularly those who are overweight or obese.
The patient can start by walking 10 minutes, 3 days a week, and can build to 30 to 45
minutes of more intense walking at least 3 days a week and increase to most, if not all,
days.
All adults should set a long-term goal to accumulate at least 30 minutes or more of
moderate-intensity physical activity on most, and preferably all, days of the week.
Reducing sedentary time is another approach to increasing activity.
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Box 13.11 Role of Physical Activity in
Weight Management
Physical activity can influence body weight three
different ways:
Prevent weight gain in the first place.
Near-daily physical activity that is continued month after month, year after
year, lowers the risk of weight gain with age.
Help one lose weight if overweight or obese.
For most overweight and obese people, the extra weight lost with exercise is
small when compared to that caused by the diet. Because most overweight
people can only exercise moderately, the actual amount of energy expended
tends to be lower than expected, and has a rather small impact on weight
loss during a 2-4 month reducing diet.
Maintain a good body weight after the excess weight is lost.
Regular physical activity is one of the best predictors of those who are able
to maintain weight loss over the long term.
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Eating Disorders
An estimated 0.5 to 3.7% of females suffer from
anorexia nervosa, and 1.1 to 4.2% in their lifetime.
85% of eating disorders have their onset during the
adolescent age period.
Among the obese, 20-40% report problems with
binge eating.
See Box 13.12 for danger signs and medical
consequences of eating disorders.
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Diagnostic Criteria for Anorexia Nervosa
DSM-IV, 1994, American Psychiatric Association
Refusal to maintain normal body weight (<85% of
expected)
Intense fear of gaining weight or becoming fat,
even though underweight
Body image disturbance
Amenorrhea (3 consecutive cycles)
Nieman DC. Exercise Testing and Prescription: A Health-Related Approach. 6/e.
Copyright ©2007 McGraw-Hill Higher Education. All rights reserved.
Binge Eating Disorder
About 25%-50% of obese people suffer from binge eating, defined as consuming
large amounts of food at one sitting while feeling out of control.
Binge eating disorder is diagnosed using these criteria:
During a binge eating episode, large amounts of food are eaten rapidly until
feeling uncomfortably full, often while alone because of embarrassment.
The amount of food eaten is definitely larger than most people would eat in a
similar period of time, and there is a feeling that one cannot stop eating or control
what or how much one is eating.
The binge eater experiences feelings of disgust, depression, and extreme guilt
after overeating.
The binge eating occurs, on average, at least two days a week for six months.
Binge eating is NOT associated with purging, fasting, or excessive exercise.
Nieman DC. Exercise Testing and Prescription: A Health-Related Approach. 6/e.
Copyright ©2007 McGraw-Hill Higher Education. All rights reserved.
Diagnostic Criteria for Bulimia Nervosa
DSM-IV, 1994, American Psychiatric Association
Recurrent episodes of binge eating (defined as
eating a large amount of food within 2 h while
feeling a lack of control)
Recurrent inappropriate compensatory behavior to
prevent weight gain (vomiting, laxatives, diuretics
enemas, medications, fasting, excessive exercise)
Binge eating and purging occur on average at least
2x/wk for 3 months
Body image disturbance
Nieman DC. Exercise Testing and Prescription: A Health-Related Approach. 6/e.
Copyright ©2007 McGraw-Hill Higher Education. All rights reserved.
Table 13.4
Risk Factors for Anorexia Nervosa
High parental education and income
Early feeding problems
Low self-esteem
High neuroticism
Maternal over-protectiveness
Eating disorders among family members
Nieman DC. Exercise Testing and Prescription: A Health-Related Approach. 6/e.
Copyright ©2007 McGraw-Hill Higher Education. All rights reserved.
Risk Factors for Bulimia Nervosa
Childhood obesity
Early onset of menarche
Weight concern
Perfectionism
Low self-esteem
Social pressure about weight and eating
Family dieting
Eating disorders among family members
Inadequate parenting
Parental discord
Parental psychopathology
Childhood sexual abuse
Chronic illness
Nieman DC. Exercise Testing and Prescription: A Health-Related Approach. 6/e.
Copyright ©2007 McGraw-Hill Higher Education. All rights reserved.