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Obesity Population Dynamics: Exploring Historical Growth and Plausible Futures in the U.S.

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Obesity Population Dynamics: Exploring Historical Growth and Plausible Futures in the U.S. Jack Homer Homer Consulting, Voorhees, NJ jhomer_at_comcast.net – PowerPoint PPT presentation

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Title: Obesity Population Dynamics: Exploring Historical Growth and Plausible Futures in the U.S.


1
Obesity Population Dynamics Exploring
Historical Growth and Plausible Futures in the
U.S.
Jack Homer Homer Consulting, Voorhees,
NJ jhomer_at_comcast.net
Bobby Milstein Syndemics Prevention Network
Centers for Disease Control and Prevention
(Atlanta, GA) BMilstein_at_cdc.gov
Bill Dietz Division of Nutrition and Physical
Activity Centers for Disease Control and
Prevention (Atlanta, GA) WDietz_at_cdc.gov
Dave Buchner Division of Nutrition and Physical
Activity Centers for Disease Control and
Prevention (Atlanta, GA) DBuchner_at_cdc.gov
Elizabeth Majestic Office of the Director
National Center for Chronic Disease Prevention
and Health Promotion Centers for Disease Control
and Prevention (Atlanta, GA) EMajestic_at_cdc.gov
International System Dynamics Conference Nijmegen,
Netherlands July 21, 2006
2
Growth of Obesity for Four Age Ranges United
States, 1960-2002
Definitions Ages 2-19 (NHES) Obese
BMIgt95th percentile on CDC growth chart Ages
2-19 (NHANES) Obese BMIgt30 or gt95th
percentile on CDC growth chart Ages 20-74
Obese BMIgt30
3
Cover of "The Economist", Dec. 13-19, 2003.
4
The Rise and Future Fall of Obesity The Why and
the How in Broad Strokes
Responses to Growth B1 Self-improvement B2
Medical response B3 Improving preventive
healthcare B4 Creating better messages B5
Creating better options in beh. settings B6
Creating better conditions in wider environ B7
Addressing related health conditions
Engines of Growth R1 Spiral of poor health and
habits R2 Parents and peer transmission R3 Media
mirrors R4 Options shape habits shape options R5
Society shapes options shape society
Drivers of Unhealthy Habits
Resources, Resistance, Benefits Supports R6
Disease care costs squeeze prevention B8 Up
front costs undercut protection efforts B9
Defending the status quo B10 Potential savings
build support R7 Broader benefits build support
Time
5
Focus of Our Simulation Model (version 6)
  • Explore effects of new interventions affecting
    caloric balance (intake less expenditure)
  • U.S. policy discourse is primarily focused on
  • prevention among school-aged youth
  • medical treatment for the severely obese
  • What are the likely consequences?
  • How much impact on adult obesity?
  • How long will it take to see?
  • Should we target other subpopulations? (age,
    sex, weight category)
  • Consider two classes of interventions
  • Changes in food activity environments
  • Weight loss/maintenance services for individuals
  • Additional intervention details (composition,
    coverage, efficacy, cost) left outside
    model boundary for now
  • Available data are inadequate to quantify impacts
    and cost-effectiveness
  • Could stakeholder Delphi help?

6
Obesity Dynamics Over the Decades Dynamic
Population Weight Framework
7
Obesity Dynamics Over the Decades Dynamic
Population Weight Framework
Dynamic Population Weight Framework
Birth
Immigration
Yearly aging
Population by Age (0-99) and Sex
Flow-rates between
Moderately
Moderately
Severely
Not
BMI categories
Overweight
Obese
Obese
Overweight
Death
Overweight and
obesity prevalence
8
Obesity Dynamics Over the Decades Dynamic
Population Weight Framework
Dynamic Population Weight Framework
Immigration
Birth
Yearly aging
Population by Age (0-99) and Sex
Caloric
Flow-rates between
Moderately
Moderately
Severely
Not
Balance
BMI categories
Overweight
Obese
Obese
Overweight
Death
Overweight and
obesity prevalence
9
Obesity Dynamics Over the Decades Two Classes of
Interventions
Dynamic Population Weight Framework
Immigration
Birth
Yearly aging
Changes in the Physical
Population by Age (0-99) and Sex
and Social Environment
Caloric
Trends and Planned
Flow-rates between
Moderately
Moderately
Severely
Not
Balance
Interventions
BMI categories
Overweight
Obese
Obese
Overweight
Weight Loss/Maintenance
Services for Individuals
Death
Overweight and
obesity prevalence
10
Obesity Dynamics Over the Decades Many
Environmental Factors Come Into Play
Options for Safe, Accessible
Physical Activity (Work,
Options for Affordable
School, Neighborhoods)
Social Influences on
Recommended Foods (Work,
Active/Inactive
School, Markets, Restaurants)
Options
Social Influences on
Consumption
Distance from Home to
Selection
Work, School, Errands
Dynamic Population Weight Framework
Food Price
Food
Activity
Environment
Environment
Electronic Media
Smoking
in the Home
Activity Limiting
Immigration
Conditions
Birth
Yearly aging
Changes in the Physical
Population by Age (0-99) and Sex
and Social Environment
Caloric
Trends and Planned
Flow-rates between
Moderately
Moderately
Severely
Not
Balance
Interventions
BMI categories
Overweight
Obese
Obese
Overweight
Weight Loss/Maintenance
Services for Individuals
Death
Overweight and
obesity prevalence
11
Information Sources
Topic Area Data Source
Prevalence of Overweight and Obesity Prevalence of Overweight and Obesity
BMI prevalence by sex and age (10 age ranges) National Health and Nutrition Examination Survey (1971-2002)
Translating Caloric Balances into BMI Flow-Rates Translating Caloric Balances into BMI Flow-Rates
BMI category cut-points for children and adolescents CDC Growth Charts
Median BMI within each BMI category National Health and Nutrition Examination Survey (1971-2002)
Median height National Health and Nutrition Examination Survey (1971-2002)
Average kilocalories per kilogram of weight change Forbes 1986
Estimating BMI Category Down-Flow Rates Estimating BMI Category Down-Flow Rates
In adults Self-reported 1-year weight change by sex and age NHANES (2001-2002) indicates 7-12 per year
In children BMI category changes by grade and starting BMI Arkansas pre-K through 12th grade assessment (2004-2005) indicates 15-28 per year
Population Composition Population Composition
Population by sex and age U.S. Census and Vital Statistics (1970-2000 and projected)
Death rates by sex and age U.S. Census and Vital Statistics (1970-2000 and projected)
Birth and immigration rates U.S. Census and Vital Statistics (1970-2000 and projected)
Influence of BMI on Mortality Influence of BMI on Mortality
Impact of BMI category on death rates by age Flegal, Graubard, et al. 2005.
12
Calibration of Uncertain Parameters To Reproduce
60 BMI Prevalence Time Series (10 age ranges x 2
sexes x 3 high-BMI categories)
  • Step 1 Iteratively adjust up-rate and down-rate
    constants and initial BMI prevalences to
    reproduce steady-state BMI prevalence for the
    early 1970s
  • Step 2 Adjust 57 caloric balance time series (by
    age, sex, and BMI category, 1975-2000) to
    reproduce BMI prevalence growth for the 1980s and
    1990s

13
Reproducing Historical Data One of 20 sex, age
Subgroups Females age 55-64
(a) Overweight fraction
(b) Obese fraction
80
50
40
60
30
Fraction of women age 55-64
Fraction of women age 55-64
40
20
20
10
0
0
1970
1975
1980
1985
1990
1995
2000
2005
1970
1975
1980
1985
1990
1995
2000
2005
NHANES
Simulated
NHANES
Simulated
(c) Severely obese fraction
25
20
15
Fraction of women age 55-64
10
5
0
1970
1975
1980
1985
1990
1995
2000
2005
NHANES
Simulated
Note S-shaped curves, with inflection in the
1990s
14
Explaining BMI Prevalence Growth Age-to-Age
Carryover Caloric Imbalance Example Females
Age 55-64
Severely obese fractions of middle-aged women
Overweight fractions of middle-aged women
Obese fractions of middle-aged women
25
80
50
20
40
60
15
30
Fraction of women by age group
Fraction of women by age group
Fraction of women by age group
40
10
20
20
5
10
0
0
0
1970
1975
1980
1985
1990
1995
2000
2005
1970
1975
1980
1985
1990
1995
2000
2005
1970
1975
1980
1985
1990
1995
2000
2005
Age 55-64
Age 45-54
Age 55-64
Age 45-54
Age 55-64
Age 45-54
Estimated caloric imbalances for women age 55-64
20
15
Kcal per day
10
5
0
1970
1975
1980
1985
1990
1995
2000
2005
Not overwt
Mod overwt
Obese
15
Assumptions for Future Scenarios
  • Base Case
  • Caloric balances stay at 2000 values through 2050
  • Altering Food and Activity Environments
  • Reduce caloric balances to their 1970 values by
    2015
  • Focused on
  • School Youth youth ages 6-19
  • All Youth all youth ages 0-19
  • SchoolParents school youth plus their parents
  • All Adults all adults ages 20
  • All Ages all youth and adults
  • Subsidized Weight Loss Programs for Obese
    Individuals
  • Net daily caloric reduction of program is 40
    calories/day (translates to 1.8 kg weight loss
    per year)
  • Fully effective by 2010 and terminated by 2020

16
Alternative Futures Obesity in Adults (20-74)
Obese fraction of Adults (Ages 20-74)
50
40
30
Fraction of popn 20-74
20
10
0
1970
1980
1990
2000
2010
2020
2030
2040
2050
Base
SchoolYouth
AllYouth
SchoolParents
AllAdults
AllAges
AllAgesWtLoss
17
Findings
  • Inflection point in obesity probably occurred
    during the 1990s
  • Simple extrapolations based on 1990s growth
    likely exaggerate
  • Caloric imbalance vs. 1970 only 1-2 (less than
    50 cal./day) within any given age, sex, and BMI
    category
  • Most of observed 9-13 cal./day increase in
    intake (USDA 1977-1996) has been natural
    consequence of weight gain (via metabolic
    adjustment), not its cause
  • Impacts of changing environments on adult obesity
    take decades to play out fully Carryover
    effect
  • Youth interventions have only small impact on
    overall adult obesity
  • Assumes (1) adult habits determined by adult
    environment, and (2) childhood overweight
    causes no irreversible metabolic changes
  • Weight-loss for the obese could accelerate
    progress--but, first, an effective program that
    minimizes recidivism must be found

18
Extras
19
An Ecological Framework for Organizing Influences
on Overweight and Obesity
Adapted from Koplan JP, Liverman CT, Kraak VI,
editors. Preventing childhood obesity health in
the balance. Washington, DC Institute of
Medicine, National Academies Press 2005.
20
BMI Category Definitions
  • For infants (ages 0-23 months)
  • Not overweight weight-for-recumbent length
    (WRL)lt85th percentile
  • Moderately overweight WRLgt85th percentile and
    lt95th percentile
  • Moderately obese WRLgt95th percentile and lt99th
    percentile
  • Severely obese WRLgt99th percentile
  • For youth (ages 2-19)
  • Not overweight BMIlt85th percentile or 25
  • Moderately overweight BMIgt85th percentile and
    25 and lt95th percentile or 30
  • Moderately obese BMIgt95th percentile and 30
    and lt99th percentile or 35
  • Severely obese BMIgt99th percentile and 35
  • For adults (ages 20)
  • Not overweight BMIlt 25
  • Moderately overweight BMIgt25 and lt30
  • Moderately obese BMIgt30 and lt35
  • Severely obese BMIgt35

21
Obesity Prevalence Over the Decades
Dynamic Population Weight Framework
22
Translating Caloric Balance Changes (?K) into
Flow Rate Changes (?F)
  • Parameters (for each age range and sex)
  • Cut-points for BMI categories (bc)
  • Median BMI within each BMI category (bm)
  • Median height (hm)
  • Assumption for the average number of kilocalories
    per kilogram of weight change (k)
  • Forbes empirical estimate of 8,050 kcal./kg
  • Implicitly takes into account the efficiency of
    weight deposition reflecting metabolic and other
    regulatory adjustments.
  • Glosses over known differences among individuals
    starting weight, composition of diet, efficiency
    of weight deposition

Forbes GB. Human body composition growth, aging,
nutrition, and activity. Springer Berlin,
Heidelberg 1987. Forbes GB. Deliberate
overfeeding in women and men Energy costs and
composition of the weight gain. British Journal
of Nutrition 561-9 1986.
23
Estimated Caloric Balances in 1990 and 2000 For
Every Age Range BMI Category (vs. 1970)
24
Reconciling the CSFII Data with Our Estimates of
Caloric Balance A Dynamic Hypothesis
Model Scope
Caloric balance
(up 1-2)
Mean BMI
(up 9-12)
25
Alternative Futures Obesity in Teens (12-19)
Obese fraction of Teens (Ages 12-19)
50
40
30
Fraction of popn 12-19
20
10
0
1970
1980
1990
2000
2010
2020
2030
2040
2050
Base
SchoolYouth
AllYouth
AllAgesWtLoss
26
Data Uncertainties Limitations
  • No reliable longitudinal data on caloric intake
    and expenditure broken out by age, sex, BMI
    category
  • Reliable NHANES data on blacks and
    Mexican-Americans only since NHANES III (1988-94)
  • NHANES prevalence estimates are imprecise
  • May affect timing of inferred growth inflection
    point
  • Down-flow rate constants are imprecise
  • Dont know to what extent historical caloric
    imbalances have led to increase in up-flows as
    opposed to decrease in down-flows
  • We have assumed entirely the former

27
Conclusions
  • This model improves our understanding of
    population dynamics of weight change and supports
    pragmatic planning/evaluation
  • No other analytical model plays out effects of
    changes in caloric balance on BMI prevalences
    over the life-course
  • Traces plausible impacts of population-level and
    individual-level interventions
  • And addresses questions of whom to target, by how
    much, and by when
  • But it has limitationssome addressable, some due
    to lack of data
  • Does not indicate exact nature of interventions
  • Does not address cost-effectiveness of
    interventions, nor political reinforcement and
    resistance
  • Does not address racial/ethnic sub-groups
  • Does not trace individual life histories
    (compartmental structure)
  • Assumes habits determined by current environment,
    not by childhood learning
  • Assumes no irreversible metabolic changes
    sustained as a result of childhood
    overweight/obesity

28
A Conventional View of Causal Forces
Wider Environment (Economy,
Health Conditions
Technology, Laws) Influence
Detracting from
Genetic Metabolic
on Healthy Diet Activity
Healthy Diet Activity
Rate Disorders
Options Available at
Prevalence of
Home, School, Work,
Healthiness of Diet
Overweight
Activity Habits
Community Influencing
Related Diseases
Healthy Diet Activity
Media Messages
Healthcare Services
Promoting Healthy
to Promote Healthy
Diet Activity
Diet Activity
29
A Conventional View of Causal Forces
  • This sort of open-loop (non-feedback) approach
  • Ignores intervention spill-over effects and often
    suggests the best strategy is a multi-pronged
    fill all needs one (even if not practical or
    affordable)
  • Ignores unintended side effects and delays that
    produce short-term vs. long-term differences in
    outcomes
  • Cannot fairly evaluate a phased approach e.g.
    bootstrapping which starts more narrowly
    targeted but then broadens and builds upon
    successes over time

30
A Closed-Loop View of Causal Forces
DRAFT 5/8/05
31
A Closed-Loop View of Causal Forces Engines of
Growth Individual Responses
DRAFT 5/8/05
32
A Closed-Loop View of Causal Forces Organized
Health Protection Efforts
DRAFT 5/8/05
33
A Closed-Loop View of Causal Forces Resources and
Resistance
DRAFT 5/8/05
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