Obesity: Pathophysiology, Risk
Assessment, and Prevalence
Obesity
• Excessive amount of body fat
• Women with > 35% body fat
• Men with > 25% body fat
• Increased risk for health problems
• Are usually overweight, but can have
healthy BMI and high % fat
• Measurements using calipers
Desirable % Body Fat
• Men: 8-25%
• Women 20-35%
Regional Distribution
• The regional distribution of body fat affects
risk factors for the heart disease and type 2
diabetes
Body Fat Distribution: Gynecoid
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•
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Lower-body obesity--Pear shape
Encouraged by estrogen and progesterone
Less health risk than upper-body obesity
After menopause, upper-body obesity
appears
Body Fat Distribution: Android
• Upper-body obesity--apple shape
• Associated with more heart disease, HTN, Type
II Diabetes
• Abdominal fat is released right into the liver
• Encouraged by testosterone and excessive
alcohol intake
• Defined as waist measurement of > 40” for men
and >35” for women
Body Fat Distribution
Weight Management
• Balancing energy intake and energy
expenditure is the basis of weight
management throughout life
Set Point Theory
• Body tends to preserve a given weight
• Energy expenditure increases and decreases
with weight loss and gain
• Effect may be temporary, e.g. energy needs
drop during calorie restriction and
normalize when energy balance is achieved
Components of Energy
Expenditure
• Resting energy expenditure: expressed as
RMR
• Energy expended in voluntary activity
• Thermic effect of food (TEF) or dietinduced thermogenesis (DIT)
• Related to energy value of food
consumed and adaptive response to
overeating
• TEF may decline as day progresses
(Romon, AJCN, 1993)
Resting Metabolic Rate
• Increases with increased muscle mass
• Declines with age
• Declines during restriction of energy intake
(up to 15%)
• Explains 60-70% of total energy
expenditure
Voluntary Energy Expenditure
(activity thermogenesis)
• The most variable component of energy
expenditure
• Accounts for 15-30% of total
• Most of us will require increasing voluntary
energy expenditure as we age to offset
declining fat free mass and RMR in order to
maintain weight
Role of Brain Neurotransmitters
• Neurotransmitters govern the body’s response to
starvation and dietary intake
• Decreases in serotonin and increases in
neuropeptide Y are associated with an increase in
carbohydrate appetite
• Neuropeptide Y increases during deprivation; may
account for increase in appetite after dieting
• Cravings for sweet high-fat foods among obese
and bulimic patients may involve the endorphin
system
Hormonal Regulation of Body
Weight
• Norepinephrine and dopamine—released
by sympathetic nervous system in
response to dietary intake
• Fasting and semistarvation lead to
decreased levels of these
neurotransmitters—more epinephrine is
made and substrate is mobilized.
Hormones and Weight
• Hypothyroidism may diminish adaptive
thermogenesis
• Insulin resistance may impair adaptive
thermogenesis
• Leptin is secreted in proportion to percent
adipose tissue and may regulate (decrease)
appetite
Hunger vs. Satiety
• Satiety—postprandial state when excess food
is being stored
• Hunger—postabsorptive state when stores are
being mobilized
• Short-term regulation affected
Hunger vs. Satiety—cont’d
• Feedback mechanism with signal from
adipose mass when weight loss occurs—
eating is the natural result
• Not always identified in the elderly
• This occurs mostly in young people
• Long-term regulation affected
Nature vs Nurture
• Identical twins raised apart have similar
weights
• Genetics account for ~40%-70% of weight
differences
• Genes affect metabolic rate, fuel use, brain
chemistry, body shape
• Thrifty metabolism gene allows for more fat
storage to protect against famine
Nature vs Nurture
Obesity tends to run in families
• If both parents are normal weight – 10%
chance of obesity in offspring
• If one parent is obese – 40% chance
• If both parents obese – 80% chance
Is it genetics or learned eating behavior?
Nurture vs Nature
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Environmental factors influence weight
Learned eating habits
Activity factor (or lack of)
Poverty and obesity
Female obesity is rooted in childhood
obesity
• Male obesity appears after age 30
Nurture vs Nature
• Overeating learned early in childhood
• Bottle vs breast
• Urging children to eat more, clean their
plates
• Use of food as a reward
Food = Love
Shelly Thorene Photography
Nature and Nurture
• Obesity is nurture allowing nature to
express itself
• Location of fat is influenced by genetics
• A child of obese parents must always be
concerned about his weight
Nature and Nurture
• The influence of
environment is apparent in
the fact that the prevalence
of obesity has increased
dramatically in the US in
the past 40 years
Causes of Obesity
Causes of Excessive Energy Intake
• Active: large portion sizes, frequent meals
and snacks
• Passive: excessive intake of energy-dense
foods containing hidden calories
• Variety of options: the greater the variety of
foods offered, the greater the intake
• Sensory-specific satiety: as foods are
consumed they become less appealing
Low Energy Expenditure
• There is a mismatch between our thrifty
metabolic genetic heritage and the sedentary
American lifestyle
Obesity is a Growing Problem
• 127 million adults in the U.S. are
overweight, 60 million obese, and 9 million
severely obese.
• 66 percent of U.S. adults are overweight
(BMI≥25)
• 32 percent are obese (BMI≥30)
• 17% of children and adolescents ages 2-19
are overweight
Obesity Trends* Among U.S. Adults
BRFSS
Prevalence of Obesity in Ohio
25
20
15
% of adults
10
5
0
1991
1995
1998
1999
2000
2001
Obesity: A Major Health Issue
• Obesity is the No. 2 preventable cause of death
and disability (smoking is #1)
• Obesity is associated with increased risk of heart
disease, stroke, gallbladder disease, cancer,
osteoarthritis, sleep apnea
• Obesity-related health problems cost $75 billion
annually (2003 data)
• The public pays about $39 billion a year -- or
about $175 per person -- for obesity through
Medicare and Medicaid programs
Health Problems Associated with
Excess Body Fat
• Surgical risk
• Lung (pulmonary)
disease
• Sleep apnea
• HTN
• CVD
• Bone and joint
disorders (gout,
osteoarthritis)
• Type 2 diabetes
• Gallstones
• Cancers (breast, colon,
pancreas, gallbladder)
• Infertility
• Pregnancy- difficult
delivery
• Reduced agility
• Early death
NHANES III Prevalence of Hypertension*
According to BMI
BMI <25
BMI 25-<27
BMI 27-<30
BMI > 30
50
41.9
37.8
Percent
40
32.7
27.7
27
30
22.1
20
15.2
14.9
10
0
Men
*Defined as mean systolic blood pressure 140 mm Hg, mean diastolic 90
mm Hg, or currently taking antihypertensive medication .
Brown C et al. Body Mass Index and the Prevalence of
Hypertension and Dyslipidemia. Obes Res. 2000;8:605-619.
Women
Obesity and Diabetes Risk
Incidence of New Cases
per 1,000 Person-Years
100
80
60
40
20
0
<20
20-25
25-30
30-35
BMI Levels
Knowler WC et al. Am J Epidemiol 1981;113:144-156.
35-40
>40
Weight Gain and Diabetes Risk
Weight Change Since Age 21
<5 kg
5-10 kg
11+ kg
25
Relative Risk
21.1
20
15
9.1
10
6.3
5
1.0
5.3
3.6
2.5
1.0
2.1
0
<22
22-23
Body Mass Index at Age 21
Adapted from Chan JM et al. Diabetes Care
1994;17:960-969.
24+
Metabolic Syndrome Criteria*
Three or more of the following abnormalities:
• Waist circumference >102 cm (40 inches) in men
and > 88 cm (35 inches) in women
• Serum triglycerides of at least 150 mg/dL
• High density lipoprotein level <40 mg/dL in men
and <50 mg/dL in women
• Blood pressure >=135/85 mm/hg
• Serum glucose >=110 mg/dl
• Includes 47 million US residents (27.7% of the
population
*ATP III Guidelines. National Cholesterol Education Program, 2001
Polycystic Ovary Syndrome (PCOS)
• Endocrine disorder characterized by
hyperandrogenism and insulin resistance
• Associated with android obesity
• Affects 5-10% of reproductive age women
• Erratic menstrual periods, chronic anovulations
resulting in multiple ovarian cysts; infertility,
acne, hirsutism and alopecia
• Increased risk of heart disease, type 2 diabetes,
reproductive cancers
Management of PCOS
• Symptom oriented, as etiology is unclear
• Individualized diet and exercise plan to
promote weight loss and normalize insulin
levels
• Medications to alleviate symptoms
26 -Year Incidence of
Coronary Heart Disease in Men
<50 years
50+ years
600
Incidence/1,000
500
440
400
300
200
366
333
350
255
177
100
0
<25
25-<30
BMI Levels
Adapted from Hubert HB et al. Circulation 1983;67:968-977.
Metropolitan Relative Weight of 110 is a BMI of approximately
25.
30+
26 -Year Incidence of
Coronary Heart Disease in Women
<50 years
50+ years
Incidence/1,000
500
400
292
268
300
223
179
200
119
100
76
0
<25
25-<30
BMI Levels
Adapted from Hubert HB et al. Circulation 1983;67:968-977.
Metropolitan Relative Weight of 110 is a BMI of approximately 25.
30+
Hypertension
20
25
30
35
40
BMI
Relationship between BMI and crude percentage of women reporting
medical problems, surgical procedures, symptoms, and health care utilization.
Brown WJ et al. Int J Obes 1998;22:520-528.
Diabetes
20
25
30
35
40
BMI
Relationship between BMI and crude percentage of women reporting
medical problems, surgical procedures, symptoms, and health care utilization.
Brown WJ et al. Int J Obes 1998;22:520-528.
Cholescystectomy
20
25
30
35
40
BMI
Relationship between BMI and crude percentage of women reporting
medical problems, surgical procedures, symptoms, and health care utilization.
Brown WJ et al. Int J Obes 1998;22:520-528.
Back Pain
20
25
30
35
40
BMI
Relationship between BMI and crude percentage of women reporting
medical problems, surgical procedures, symptoms, and health care utilization.
Brown WJ et al. Int J Obes 1998;22:520-528.
Body Mass Index and Mortality Risk
(Adapted from Bray GA. Gray DS, Obesity, part 1: Pathogenesis. West J Med 149:429, 1988; and Lew EA, Garfinkle L; Variations
in mortality by weight among 750,000 men and women. J Clin Epidemiol 32:563, 1979.)
BMI and Health
Below 18.5
Underweight
18.5 – 24.9
Normal
25.0 – 29.9
Overweight
Monitor for risk
Obese
Increased health risk
Severely obese
Major health risk
30.0 and Above
40.0 and above