Transcript Obesity - Up to the Theory Home Page

Welcome to Session on
Obesity
Meera Kaur, PhD, RD
Assistant Professor
Department of Family Medicine
Faculty of Medicine
[email protected]
http://home.cc.umanitoba.ca/~kaur
Outline
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Learning objectives
Introduction
Classification and diagnosis
Obesity trend
Adipose tissue, adiposity, hypertrophy and hyperplasia
Energy balance
Regulation of body weight
Regulation of food intake and body weight
Regulatory factors in feeding and adiposity
Sound weight loss program
Conclusions
Questions and answers
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Learning Objectives
• To understand
– the physiological and metabolic
perspectives of obesity/overweight, and
– the regulation of body weight with special
reference to:
• Regulatory factors involved in feeding and
adiposity
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Introduction
• Obesity is the disorder of body composition defined by a relative
or absolute excess of body fat.
• The WHO and NHLBI have classified obesity as an epidemic
• In 2002, ~64% Americans overweight; 32% obese
• 16% or 9 million kids were overweight
• Thus, a trend towards an ever-fatter America
• By 2009, 70% of American expected to be overweight or obese
• Obesity contributes to +300,000 deaths a year
• From a global perspective, the increase in the prevalence of
obesity is alarming
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Classification and Diagnosis
Classification
BMI (kg/m2)
Risk of Co-morbidities
Underweight
<18.5
increased risk in other areas
Desirable
18.5-24.9
Average
Overweight
25.0-29.9
Mildly Increased
Obese
>30.0
Class I Obesity
30.0-34.9
Moderate
Class II Obesity
35.0-39.9
Severe
Class III Obesity
>40.0
Very severe
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Classification for Children (<2 Years)
BMI Status
Normal weight for height
At risk for overweight
Overweight
10th-90th percentile
85th-95th percentile
>95 percentile
(Centre for Disease Control and Prevention, 2005)
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Assessing Obesity
• Waist circumference at level of iliac crest
– Above 40 inches for men and 35 inches for
women are indicative of health risk.
• Waist-to-hip ratio: Circumference of the waist
at the level of L3 divided by the
circumference of the hip at the largest area of
the gluteal region. (Helps identify central or
android obesity.)
– For men waist-to-hip ratio > 1
– For women waist-to-hip ratio > 0.85
Obesity Trends in US Adults
1991
1993
1995
1998
< 10%
10% to 15%
> 15%
AH, et al. JAMA. 1999
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Obesity Trends in US Adults…
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Obesity Trends in US Adults, 2004
No Data
<10%
10%–14%
15%–19%
20%–24%
≥25%
Adipose Tissue, Adipocytes,
Hypertrophy and Hyperplasia
• Adipose tissue
– White: energy, cushion, insulation
– Brown: Key regulator of energy expenditure
• Adipocytes
– store 80-90% fat as tryglyceride
• Hypertrophy
–  adipose tissue due to enlarged adipocytes
• Hyperplasia
–  adipose tissue due to  number of adipocytes
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Juvenile-Onset Obesity
• Develops in infancy or childhood
• Increase in the number of adipose cells
• Adipose cells have long life span and need to
store fat
• Makes it difficult to lose the fat (weight loss)
• Causes
– poor dietary patterns
– lack of physical activity
• 43% of adolescents watch 2 hours or more of
TV/day
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Adult-Onset Obesity
• Develops in adulthood
• Fewer (number of) adipose cells
• These adipose cells are larger (stores excess
amount of fat)
• If weight gain continues, the number of
adipose cells can increase
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Regulation of Body Weight
• Short-term regulation is governed by:
– Hunger (postabsorptive), appetite and satiety
(postprandial)
– physical trigger for hunger > satiety
• Long-term regulation is governed by:
– feedback mechanism– adipocytokines (signaling
protein is released from the adipose mass when
normal body composition is disturbed. This
mechanism plays a greater role in younger
persons than older adults.
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Set-Point Theory
• Fat storage in nonobase adult is regulated to
preserve the specific weight.
– deliberate effort to starve or overfeed are followed by
a rapid return to original body weight (set-point).
– if set-point theory is true, some form of obesity could
be due to the abnormally established set-point.
• Can we establish a new settling-point vs. Setpoint to treat obesity?
– However, data are not conclusive in this area. We
need to do more research.
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Energy Production
Energy Balance…
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• State in which energy intake, in the form of food and
/or alcohol, matches the energy expended, primarily
through basal metabolism and physical activity
• Positive energy balance
Energy intake > energy expended
Results in weight gain
• Negative energy balance
Energy intake < energy
Results in weight loss
Energy Balance
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Regulation of Energy Intake and
Body Weight
• Factors that regulate energy intake and body
weights are:
– Dietary thermogenesis and the Thermic Effect of
Foods (TEF)/Specific Dynamic Action (SDA) of
foods
– Resting/Basal Metabolic Rate (RMR)/(BMR)
– Energy expended in voluntary activity
– Regulatory neurotransmitters and hormones
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Thermic Effect of Foods
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Energy used to digest, absorb, and
metabolize food nutrients
“Sales tax” of total energy consumed
~5-10% above the total energy consumed
TEF is higher for CHO and protein than fat
Less energy is used to transfer dietary fat
into adipose stores
– Meal size, meal composition, previous meal,
insulin resistance, physical activity and aging
influence the TEF.
– Aerobic exercise the TEF
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Resting Metabolic Rate (RMR)
• RMR explains 60-70% of Total Energy expenditure
(TEE). When body is deprived of energy
– RMR adapts to conserve energy by dropping
rapidly (up to 15% in two weeks).
• RMR declines with age
• During undernutrition, abnormalities in lipolysis may
cause insulin resistance affecting RMR
• The regulation of free fatty acid availability is an
important area of research related to the RMR.
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Activity Thermogenesis (AT)
• Energy expended in voluntary activity – activity
thermogenesis (AT) is the most important component
of TEE (15-30% normally). Therefore, AT should be 
when energy is not restricted.
• RMR and Fat free mass (FFM) decrease with age.
Hence adjustment between energy intake and AT
should be adjusted for preserving normal weight.
• All activity counts including nonexcercise activity
thermogenesis (NEAT).
• To reverse obesity standing and ambulatory time
should be promoted at least 2.5 hours/day.
Energy Balance
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Ultimate Energy Balance
TEF
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Dietary
Intake
NEAT
Physical
activity
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Macronutrients and Fat Storage
• Body prefers to use CHO as energy source
• Only excess intake of CHO and protein will be
turned into fat
• Fat will remain as fat for storage
• Physical activity encourages the burning of
dietary fat (Beta-oxidation)
• High CHO diet decreases Beta-oxidation
• Most endurance athletes burn fatty acids for
energy
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Fat Storage
• Fat
– Most fat is stored directly into adipose tissue
– Body has ability to store fat (as fat)
• Carbohydrates
– Limited CHO can be stored as glycogen Most CHO is
used as a energy source
– Excessive CHO will be synthesized into fat (for
storage)
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Protein and Fat Storage
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Protein is primarily used for tissue synthesis
Adults generally consume more protein than
needed for tissue synthesis
Excess protein is used as a energy source
Some protein will be synthesized into fat
(for storage)
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Regulatory Factors in Feeding
and Adiposity
• Brain Neurotransmitters
• Gut hormones
• Other hormones
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Brain Neurotransmitters
• Norepinephrine and Dopamine
– Released by symphathetic nervous system (SNS)
– Fasting & starvation  SNS activity, epinephrine that
govern feeding behaviour and subatrate mobilization
– Dopaminnergic pathway in the brain play a role in
reinforcement properties of foodds.
• Serotonin
–  In serotonin leads to carbohydrate appetite.
• Corticotrophin-releasing Factor (CRF)
– CRF is a potent anorexic agent and weakens the feeding
response produced by norepinephrine and neuropeptide Y.
– CRF is released during exercise.
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Gut Hormones…
• Incretins is a G-I peptide
–  insulin release after eating , even before blood glucose
level is elevated. Serotonin is a G-I peptide
• Cholecystokinin (CCK)
– At brain level inhibits food intake. Stimulates pancreatic
enzymes
• Bombesin
–  Food intake and enhances the release of CCK.
• Enterostatin
– Part of pancreatic lipase;  satiety following fat consumption
Gut Hormones
• Adiponectin - Adipocytokine secreted by adipose tissue
– Level of this hormone is inversely related to BMI. Plays role in
metabolic disorders.
• Glucagon causes hypoglycemia
• Glucagon-like-peptide-1 (GLP-1)
– Released in presence of glucose rich food, delays gastric emptying
time and promote satiety.
• Leptin is an adipocytokine and regulates appetite.
– In obesity it loses the ability to inhibit energy intake.
• Resistin - An adipocytokine that antagonizes insulin action
• Ghrelin – Produced in stomach and stimulate hunger.
• Peotide YY-3-36 (PYY -3-36 ) is secreted in small bowel in response to
foods.
– In obesity it loses the ability to inhibit energy intake.
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Other Hormones
• Thyroid hormone – Modulates the tissue
responsiveness to the catecholamines secreted by
SNS. A  in thyroid hormone lpwers the SNS
activity and adaptive thermogenesis.
• Vispatin - An adipocytokine protein that has an
insulin-like-effect. Plasma level  with  adiposity
and insulin resistance.
• Adrenomedullin - A new peptide secreted by
adipocytesas a result of inflammatory process
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Satiety Regulator
• The hypothalamus
– When feeding cells are stimulated, they signal us
to eat
– When satiety cells are stimulated, they signal us to
stop eating
• Sympathetic nervous system
– When activity increases, it signals us to stop
eating
– When activity decreases, it signals us to eat
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Influences of Satiety…
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Influences of Satiety
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What it Takes to Lose a Pound
• Body fat contains 3500 kcal per pound
• Fat storage (body fat plus supporting lean
tissues) contains 2700 kcal per pound
• Must have an energy deficit of 2700-3500
kcal to lose a pound per week
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Do the Math
To lose one pound, you must create a deficit of 2700-3500 kcal
So to lose a pound in 1 week (7 days), try cutting back on your
kcal intake and increase physical activity so that you create
a deficit of 400-500 kcal per day
- 500 kcal x 7 days = - 3500 kcal = 1 pound of weight loss
day
week
in 1 week
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Sound Weight Loss Program
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Meets nutritional needs, except for kcal
Slow & steady weight loss
Adapted to individuals’ habits and tastes
Contains enough kcal to minimize hunger and fatigue
Contains common foods
Fit into any social situation
Change eating problems/habits
Improves overall health
See a physician before starting
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Summary and Conclusion
• To treat obesity and/or develop an effective weight
loss program, understanding of
– the physiological and metabolic perspectives of
obesity/overweight is important
– the regulation of body weight with special
reference to:
• Regulatory factors involved in feeding and adiposity is
crucial
– Energy balance is the key point
– Team approach is important in developing a
sustainable weight loss program
Thank you
for gracing the session!
Any question?