Effective or sustainable prevention strategies for obesity, particularly in youths,
have been elusive since the recognition of obesity as a major public health issue
2 decades ago. Although many advances have been made with regard to the basic biology
of adiposity and behavioral modifications at the individual level, little success
has been achieved in either preventing further weight gain or maintaining weight loss
on a population level (1). To a great extent, this is the result of the complex task
of trying to change the way people eat, move, and live, and sustaining those changes
over time.
The most immediate cause of obesity is an imbalance of energy intake and energy expenditure
in the body. This energy imbalance, on the magnitude seen in today's population, arises
from the complex interactions of biological susceptibilities and socioenvironmental
changes (2). Evidence in behavioral economics suggests that these powerful biological
and contextual forces often place eating and exercise behavior beyond an individual's
rational control (3). Therefore, the solution to the obesity epidemic lies in policies
and interventions that alter those contextual features, taking individual biology
and preferences into account. Historically, obesity research has been conducted within
individual disciplines. Now, for both scientific inquiry and for public policies,
obesity should be framed as a complex system in which behavior is affected by multiple
individual-level factors and socioenvironmental factors (ie, factors related to the
food, physical, cultural, or economic environment that enable or constrain human behavior,
or both). These factors are heterogeneous and interdependent, and they interact dynamically
(4).
Because of the complex system that affects obesity, researchers need to use a systems-oriented
approach to address the multiple factors and levels. Whereas multidisciplinary research
consists of teams with different expertise that can contribute to the understanding
of particular aspects of a larger research question, truly cross-disciplinary research
asks a priori questions and poses hypotheses that cut across disciplines and across
levels of influence. For example, how do biological mechanisms of energy metabolism
react to or how are they affected by different features of the built, social, or economic
environment to produce a given distribution of eating or physical activity? How do
these conditions enable or constrain eating and physical activity, and how are they
embodied in biological systems to affect these behaviors?
In October 2007, the Eunice Kennedy Shriver National Institute of Child Health and
Human Development (NICHD) convened the international conference Beyond Individual
Behavior: Multidimensional Research in Obesity Linking Biology to Society. The goal
was to create a climate of training, funding, and academic and institutional support
for obesity research that will offer sustainable solutions to the obesity problem.
Participants hoped to bridge the factors that influence obesity-related behaviors
at the macro level (typically policies that shape and govern the food, physical, social,
and economic environments in which we live) and the micro level (typically variables
within people or their immediate surroundings that influence health outcomes). The
conference was supported by the National Institutes of Health (National Cancer Institute;
National Institute of Diabetes and Digestive and Kidney Diseases; National Heart,
Lung, and Blood Institute; Division of Nutrition Research Coordination, Office of
Behavioral and Social Sciences Research; and Office of Disease Prevention), the Canadian
Institutes of Health Research (Institute of Nutrition, Metabolism, and Diabetes),
and the Centers for Disease Control and Prevention. The content of this 3-day conference
was designed to explicate the scientific foundation of this multilevel approach, generate
research questions that apply to all disciplines, consider different intervention
models, and discuss methods needed for the design and analysis of systems-oriented,
multilevel studies (5). The essential elements of this multilevel agenda are framing
obesity as a complex systems problem; encouraging cross-disciplinary questions and
hypotheses; focusing on structural interventions (ie, modifications to the environment
or policies); building capacity for multilevel research and action; and taking a global
perspective.
Theoretical Framework of the Multilevel Model to Address Obesity
Multilevel models are not new in public health; the concept stems from socioecological
theories (6) that emphasize the importance of social and environmental factors in
determining human behavior and health outcomes. However, the model has been interpreted
to describe ecologic layers without elaborating on multiple sectors operating at multiple
levels or including bidirectional interactions of factors (7). Glass and McAtee (8)
present a multilevel model that is useful to address the complex, interacting contexts
for obesity prevention. This model (Figure 1), which was a key focal point for the
international conference, integrates biological (genes, cells, and organs) and socioenvironmental
(economics, culture, social networks, and features of the physical environment) influences
on behaviors such as eating and physical activity. Time, on the horizontal axis, is
in the context of life course (conception to death) at the individual level or social
change at the population level. The vertical axis depicts a nested hierarchy of systems
including biological, social, and environmental influences (8). This model shows that
the behaviors leading to health outcomes, not just health outcomes per se, are influenced
by biological or socioenvironmental factors.
Figure 1
A systems-oriented, multilevel model applied to the study of obesity. The contingent
effects of risk regulators (ie, embodiment, opportunity, and constraint) are shown
with dotted arrows. "Causal" effects of biological and behavioral variables are shown
with solid arrows. Feedback loops existing within grouped variables are not shown.
Specific effects and multiple, time-ordered feedback loops between variables are not
shown in order to reduce diagram complexity. Reprinted with permission from Elsevier
(8).
Process chart
The two main axes are the hierarchical axis, running from bottom to top, and the time
axis, running from left to right. At the intersection of these two axes is birth weight
and early exposures. From that point and moving to the right through time are health
behaviors that include energy input (feeding behavior) and energy expenditure (physical
activity). From these Health behaviors, continuing across through time, there is body
weight change. A line indicates there is a causal connection between birth weight
and early exposures and body weight change.
Connected to body weight change is a line showing a feedback loop back and forth to
this group of factors: HPA axis, mood, metabolism, appetite, and genes; these also
are connected back and forth with health behaviors as causal effects.
At the top of the hierarchical axis is a group of risk regulators: cultural norms
(eg, food preferences, body-image norms), area deprivation (eg, poverty, crowding),
psychosocial hazards (eg, crime, social disorganization), built environments (eg,
connectivity, walkability), local food environment (eg, availability of fruits/veg,
presence of fast food), and commercial messaging.
This group is connected to health behaviors by a contingent (indirect) effect and
to the factors HPA axis, mood, metabolism, appetite, and genes.
The model is consistent with economics and psychology in that people are assumed to
engage in behaviors based on preferences and attitudes. It becomes multilevel in that
a person is constrained by factors that exert regulatory control on those behaviors.
For example, food choices are made not just on the basis of preferences but also on
the basis of the price of food, the cultural meaning of food, the availability of
food, and the biological responses to the reward value of food. The distribution of
these parameters constitutes a behavioral niche or landscape, to which the person
must adapt and respond according to particular goals and intentions. The movement
in time of higher or lower rates of obesity is, therefore, the result of multiply-dependent
and interlocking systems. There are 4 possible implications. First, a single cause
of the obesity epidemic is unlikely. Second, the processes that give rise to increasing
average body size probably involve combinations of factors at multiple levels of influence.
Third, small changes in 1 or more key factors may have large and potentially nonlinear
influences on distribution of body weight. Finally, both socioenvironmental factors
and biological processes are involved in the expression of human behavior.
One problem with building a systems-oriented, multilevel framework for obesity is
that key influences in the physical or economic environment may not fit conventional
definitions of causes. Glass and McAtee contend that social factors, such as social
inequity and poverty, are difficult to study from a traditional epidemiologic standpoint,
in part because they do not fit the definition of a causal risk factor (8). An alternative
view of these variables is to define them as risk regulators, or dynamic components
of interconnected systems that influence obesity-related behaviors from the personal
level to the public policy level (8). Systems of food distribution alter the probabilities
at a population level that these causes will align in ways that lead to different
rates of obesity (9). The search for a set of key risk regulators provides greater
room to consider the social, physical, cultural, and economic environments that influence
obesity.
The concept of risk regulators also may help overcome some of the disadvantages of
conventional socio-ecological models, namely the lack of clarity on what is most important,
where the key drivers are located, or what the optimal intervention points are. The
multiple levels (individual vs community) require a bridging structure, which act
as conduits between macro-level forces and the factors in the local environment that
govern eating and activity. The temporally and spatially distal forces that operate
at the macro level cascade through organizations, through systems of food distribution,
through policies and pricing, and eventually shape the reality that people perceive
in their lives. Examples of the bridging in the case of obesity could be cultural
norms, social networks, local food availability, food prices and taxes, physical activity
amenities, psychosocial stress, or economic insecurity. These might act through neurologic
or epigenetic regulatory pathways to affect behavior and to generate feedback loops
higher in the system. Epigenetic pathways are phenotypic differences between individuals
that are not a result of genetic composition per se but a result of alterations in
genetic expression through the silencing of genes or interference with genetic transcription.
Forming Cross-Disciplinary Questions and Hypotheses for Research
Diverse sectors of society operate at different levels to influence population energy
balance (Figure 2) (2,10). Factors can range from the individual level to the international
level, and the sectors of influence include education, agriculture, transportation,
urban developments, and media, among others, in addition to the health sector. Research
that cuts across these different levels and sectors can be undertaken (Figure 2).
Figure 2
Prevalence (95% confidence interval) of obesity among children (2-19 years, age adjusted),
according to family income as a percentage of the federal poverty level; the federal
poverty level during 2004 was $18,850 for a family of 4 (7). Data source: National
Health and Nutrition Examination Survey, 1999-2004.
Bar chart
This model shows the determinants that influence population energy balance at different
levels. From left to right, they are International Factors, National/Regional, Community/Locality,
Work/School/Home, and Individual, which lead to the population outcome Obesity Prevalence.
Within International Factors, the sectors are Globalization of markets, Development,
and Media programs and advertising.
Globalization of markets is linked in International Factors to Development, in Community/Locality
to Public Transport, and in Work/School/Home to Leisure Activity/Facilities.
Development is linked in National/Regional to Urbanization, to Health, and to Food
and Nutrition, in Community/Locality to Agriculture/Gardens/Local markets, and in
Work/School/Home to Leisure Activity/Facilities and to Labour.
Media programs and advertising is linked in National/Regional to Media and Culture,
to Education, and to Food and Nutrition.
Between the International Factors and National/Regional is a marker denoting the National
perspective that is also a factor in the model.
Within National/Regional, the sectors are Transport, Urbanization, Health, Social
Security, Media and Culture, Education, and Food and Nutrition.
In National/Regional, the Transport sector and the Food and Nutrition sector are linked
together, and the link between these two is linked in Community/Locality to Manufactured/Imported
Food. The Urbanization sector, Health sector, and Food and Nutrition sector are linked
together.
Transport is linked in Community/Locality to Public Transport and to Public Safety.
Urbanization is linked in Community/Locality to Public Transport, to Public Safety,
and to Sanitation.
Health is linked in Community/Locality to Health Care and to Sanitation.
Social Security is linked in Work/School/Home to Leisure Activity/Facilities, to Family
and Home, and to School Food and Activity.
Media and Culture is linked in Community/Locality to Manufactured/Imported Food, and
in Work/School/Home to Worksite Food and Activity and to Family and Home.
Education is linked in Work/School/Home to Family and Home and to School Food and
Activity.
Food and Nutrition is linked in Community/Locality to Manufactured/Imported Food and
to Agriculture/Gardens/Local markets, and is linked in Work/School/Home to Family
and Home and to School Food and Activity.
Within Community/Locality, the sectors are Public Transport, Public Safety, Health
Care, Sanitation, Manufactured/Imported Food, and Agriculture/Gardens/Local Markets.
Public Transport is linked in the Individual sector to Energy Expenditure.
Public Safety is linked in Work/School/Home to Leisure Activity/Facilities and in
the Individual sector to Energy Expenditure.
Health care is linked in Work/School/Home to Infections.
Sanitation is linked in Work/School/Home to Infections.
Manufactured/Imported Food is linked in Work/School/Home to Worksite Food and Activity,
to Family and Home, and to School Food and Activity, and in the Individual sector
to Food intake: Nutrient density.
Agriculture/Gardens/Local markets is linked in Work/School/Home to Family and Home
and to School Food and Activity, and in the Individual sector to Food intake: Nutrient
density.
Within Work/School/Home, the sectors are Leisure Activity/Facilities, Labour, Infections,
Worksite Food and Activity, Family and Home, and School Food and Activity.
Leisure Activity/Facilities is linked in the Individual sector to Energy Expenditure.
Labour is linked in the Individual sector to Energy Expenditure.
Infections, Worksite Food and Activity, Family and Home, and School Food and Activity
are each linked in the Individual sector to Energy Expenditure and to Food intake:
Nutrient density.
Within Individual are 2 sectors, Energy Expenditure and Food intake: Nutrient density.
Both are linked separately and together to the population outcome, Obesity Prevalence.
Obesity as a function of biology
The simplest biological view of obesity is that energy intake (increased) and expenditure
(decreased) became discordant over time. A decreased sensitivity to metabolic signals
that inhibit overeating is highly adaptive for survival in circumstances where food
availability is limited or cyclic, by permitting storage of excess energy, when available,
as body fat. However, when an abundance of cheap, readily available, and palatable
(eg, high-fat, high-sugar) food is in the environment, this raised threshold of metabolic
tolerance promotes obesity (11). Failures in weight loss attempts are, in part, the
result of powerful biological drives to store and maintain energy in the body.
An obesogenic prenatal environment can also increase the likelihood of obesity in
the offspring through epigenetic effects (12). These epigenetic factors can be seen
as biological risk regulators that might help explain, in part, how the environment
is embodied in metabolic systems to affect behavior and health.
In animal studies, many prenatal manipulations appear to promote offspring obesity
by permanently altering the development of central neural pathways that regulate food
intake, energy expenditure, and energy storage (13). Human imaging studies suggest
that the brain has automatic approach responses to food compared with nonfood objects
(14) and that these responses can be influenced by product advertising (15) and pricing
(16). The reward and executive control patterns in the brain can be induced and modulated
by palatable, energy-dense foods in a way similar to addictive substances (17). These
neural systems are powerful in defending the body from undernutrition but have little
capacity to defend against overnutrition and upper limits of body weight and adiposity
(18). So, what other factors in the environment trigger or alter people's biological
response to food to make them eat in a way that promotes weight gain? Recent research
points to elements of the social and physical environment, and emerging evidence also
suggests that the economic and policy environment plays an important role. However,
this area of research remains in its infancy. Furthermore, almost no research explores
how macro-level variables influence biological processes to result in differential
behavioral phenotypes or how biological drivers of obesity are affected by different
socioenvironmental conditions.
Haemer et al (19) in this issue of Preventing Chronic Disease, explore in greater
detail the biological risk regulators of obesity. In addition, Esposito et al (20)
offer a developmental perspective to understanding how additional biopsychological
factors interact with the family and school context to shape food preferences in children.
Obesity as a function of the built environment
The availability, accessibility, and marketing of foods all contribute to our consumption
patterns, either directly by enabling or constraining food choices or indirectly by
modulating biological processes to affect eating. In the United States, the availability
and accessibility of healthy foods, such as fresh produce, are often limited, particularly
in poor or rural communities (21). Marketing of high-calorie foods via packaging,
retail, and media to children has increased purchase and consumption of those foods
(22).
Many features of the built physical environment may also affect energy expenditure.
The lack of perceived safety, lack of facilities, and low access to key destinations
(eg, inconvenient transportation) are some of the factors that inhibit or decrease
physical activity levels (23). Physical activity improves insulin sensitivity, glucose
homeostasis, and other metabolic profiles (24), which in turn can have an impact on
adiposity (25). Reducing sedentary activity (eg, television viewing, computer usage)
in children reduces obesity, but this effect appears to be mediated via a reduction
in energy intake rather than an increase in physical activity (26). If so, neurologic
responses may also act as mediators between sedentary activity and obesity.
With the emergence of geographic information systems technology, studying the built
environment with objective measures in relation to obesity is now more feasible. Mechanisms
of the association between the built environment and obesity remain poorly understood,
particularly in terms of how the built environment interacts with biology to influence
obesity-related behaviors. As Figure 1 illustrates, one should not assume that the
relationships between environmental factors and health behavior are direct or linear.
Obesity as a function of the social environment
Norms of food and physical activity behaviors and body image ideals vary by culture.
Overweight in a child, for example, is viewed as a symbol of health by some cultures
(27). In a simple computational experiment, Hammond (28) showed that changing norms
of body weight, as the population becomes increasingly obese over time, could in themselves
propagate obesity.
Cultural forces can also be barriers to obesity prevention. For instance, the American
culture places a strong emphasis on individual responsibility over one's own lifestyle
or the lifestyle of one's child. This cultural underpinning, in part, led to the conventional
emphasis on research and programs to educate or train people how to behave in healthier
ways. However, such individual-oriented approaches, which usually do not take into
account biological and socioenvironmental drivers of behaviors, have rarely worked
over the long term (29). Overcoming this fundamental aspect of our sociopolitical
culture must be considered in a long-term solution to obesity.
Although many harmful social conditions (eg, poverty, pollution) can end lives prematurely,
they are not susceptible to change by those most affected (ie, minority ethnic groups
and children). Therefore, interventions that rely on individual health promotion alone
will bias outcomes toward the more advantaged segments of the population, who have
more choices about changing their environments. Examining health disparities through
the lens of social disadvantage (eg, deprivation, discrimination-exclusion) rather
than epidemiologic trends alone will influence research questions, comparisons, variables,
and subgroups. Braveman discusses these concerns in this issue of Preventing Chronic
Disease (30).
An increase in chronic stress (31) may be a way through which social conditions interact
with biological processes to affect obesity-related behavior. Stress stimulates opioid
release in the reward center of the brain, which is a defense mechanism for the body
to attenuate the detrimental effects of stress. Chronic stress can repeatedly stimulate
the reward pathways and further enhance the reward value of food, possibly contributing
to increased energy intake and fat accumulation over time (32).
Obesity as a function of economics
In the United States, data suggest that poverty is associated with higher obesity
rates (33), whereas in many developing countries, higher rates of obesity are found
in higher-income groups as a result of economic growth and improved standards of living
(34). One explanation for these observations is that low-income groups in the United
States and high-income groups in developing countries either are better able to afford
or have greater access to energy-dense but nutrient-poor foods (35). These foods have
high proportions of dietary fats, sugar, and refined grains, the cost of which has
steadily decreased while the supply has steadily increased over the last 40 years
(36). Nutrient-rich and energy-poor diets have much higher costs per calorie (37).
Therefore, a testable hypothesis linking macro-level economics to obesity is that
the higher cost of healthy foods may lead to financial stress. This, coupled with
the higher availability, accessibility, and marketing of unhealthy foods in poorer
neighborhoods, may lead to increased purchase and consumption of unhealthy foods,
which over time results in increased obesity. Subsequently, increased obesity in the
population can perpetuate itself through intergenerational epigenetic programming.
The food industry determines agricultural production, food manufacturing, processing,
packaging, transport, retail, and marketing to influence the eating patterns of populations
(38). The supply side of the food chain can be influenced by agricultural policies
on farm output, while the demand side can be influenced by variables such as income,
availability, and pricing. Furthermore, the foods that farmers choose to grow are
influenced by policies that support some foods more than others; for example, corn
and soybeans have, in general, more support than fruits and vegetables. It remains
to be investigated how the different economic facets of food cause obesity variation
across countries and people, how much can be attributed to the role of policy in affecting
producer and consumer behavior, and how food production chains can be modified to
shape future consumer demand for healthier food options.
Structural Modifications to Multilevel Interventions
The next-generation interventions for obesity should start at the community level
or higher, with multiple stakeholders that connect people, families, schools, government,
and the private sector. Intervention activities should include not only educational
schemes but also environmental changes to shift norms and enable the adoption of healthy
behaviors within everyday life. The family, schools, primary care settings, and municipalities
can be targeted simultaneously as catchment sites to interface with children and parents.
Media organizations and businesses (eg, food manufacturers, retailers, supermarkets,
the transportation industry) can also help shift norms, effectively contributing to
both the supply and demand sides of the energy balance equation.
Much can be learned from the North Karelia Project in Finland from the 1970s through
the 1990s, where that country's public health agency transformed the lifestyle pattern
of Finnish communities to reduce smoking rates and improve dietary practices. The
Finland project did not rely exclusively on individually focused educational interventions.
The government created incentives for farmers to switch from meat to fruit and vegetable
production, and worked through social networks by using community organizations. There
were also efforts to use regulatory changes to influence the nutrient content of food
(eg, requiring sausage makers to lower the fat content of their products across the
entire market). The result was a greater than 50% reduction in coronary heart disease
mortality, as well as reductions in stroke, cancer, and other diseases, in the entire
country within 20 years (39).
Although research on multilevel interventions advances slowly, actions are already
being taken in many US and international communities. This parallel movement at the
grassroots level needs to be taken advantage of with rigorous evaluations to determine
the effect of community-initiated interventions (40). There is little research on
the dissemination and diffusion requirements of multilevel interventions. As intervention
and evaluation research continue, dissemination must be part of the strategic effort.
Capacity Building for Multilevel Research and Action
Multilevel research and interventions cannot be conducted or sustained if the agenda
does not include a strong focus on building coalitions across societal sectors and
increasing the capacity to tackle obesity (41). Specifically, public-private partnerships,
leadership of national governments, and training of future multilevel researchers
and policy makers are warranted.
Public-private partnerships
Every person and every sector in society are important in a multilevel approach to
obesity. The food industry and industries that shape our built environment have a
role to play and should be invited to this research forum as partners (see Huang and
Yaroch [42]). Industry not only shapes the physical landscape of our environment but
also shapes values and norms. There is a need to agree on a public-private partnership
framework that outlines the rules of these collaborations. Specifically, this framework
must affirm that trade and health are not mutually exclusive. It should articulate
issues related to trust-building, information sharing and technical cooperation, transparency
of individual and collaborative efforts, and pooling of resources. Successful partnerships
must be constructed through open, honest, and regular dialogues. As with any relationship,
the partners must be willing to take risks and to compromise to find common ground.
In addition, there must be leaders to champion the partnership and the cause the partnership
represents. Finally, sufficient resources must be made available to implement any
actions jointly developed by the partnership.
Role of national governments
The experience in North Karelia and experiences in tackling tobacco use in the United
States and other countries (43) suggest that top-down strategies must accompany bottom-up
approaches to sustain the necessary environmental and behavioral changes to prevent
obesity. Although individual-level interventions have been effective in reducing smoking,
their effect never could have been sustained or scaled up to the population level
in the absence of regulatory and economic interventions by the government (44). Many
policy options have been proposed elsewhere (45), but few have been tested or evaluated
to ascertain the evidence of cost-effectiveness.
National governments also play a critical role in facilitating and coordinating research
and then translating research into programs and policies. Coordination is essential
among government and nongovernment agencies as well as among different sectors in
society. Leadership at the national level often is necessary to move a multilevel
agenda forward. For example, since 2005 the Institute of Medicine has called for a
national strategy on childhood obesity that cuts across government agencies and societal
sectors (46), but such a national mandate has yet to be established (47).
Training
Training of future scientists is an indispensable component of the long-term viability
of any multilevel research agenda. Medical and public health training contain little
to no curriculum on systems science. A coordinated effort is needed to develop training
in a "multilevel science" in public health. Training should include not only the knowledge
base of obesity and chronic disease prevention in general but also methodologic expertise
for the design and analysis of multilevel studies, including novel statistical and
computational approaches. Hammond discusses this training need in this issue (48).
Training should be integrated at the predoctoral, postdoctoral, and midcareer levels.
Obesity From a Global Perspective
In the world, approximately 22 million children younger than age 5 years are overweight.
By 2015, an estimated 2.3 billion people aged 15 or older will be overweight and 700
million will be obese worldwide (49). By 2010, cardiovascular disease will be the
leading cause of death in developing countries, and by 2030 more than 280 million
people in developing countries will have type 2 diabetes (49). Key drivers of these
numbers are transnational (globalization of markets and media, urbanization, trade,
economic growth, food availability, marketing) (Figure 2), requiring a global perspective
to address obesity. The increasing health effects related to obesity will pose substantial
economic challenges as a result of cost and insufficient infrastructure in the world's
health care systems (50). An unhealthy population leads to reduced economic productivity,
which further exacerbates morbidity and mortality.
Experiences in the United States and other developed nations may serve as a starting
point for understanding and combating obesity in developing countries. Nevertheless,
factors may not all be equally relevant in different countries, and environmental,
cultural, and sociopolitical influences within countries determine what types of solutions
will be feasible and effective. More international research is needed to understand
these differences. For example, the Seven Countries Study (51) on cardiovascular health
provided great insight into the role of population-level variations in diet in heart
disease risk. Although ecologic correlations are weak for supporting causal inference,
this study was groundbreaking in showing population-level influences on disease rates
and on preventive strategies. Obesity research can carry on these lessons. International
research that capitalizes on the contrast on either differing obesity rates or differing
socioenvironmental characteristics across contexts can be especially illuminating.
Conclusions
Current levels of obesity reflect complex social changes and biological susceptibilities,
and their interactions, during the last 40 years. Individual behaviors such as eating
and physical activity do not occur in a vacuum; rather, they are influenced by socioenvironmental
factors and by powerful biological processes. Behavior change cannot be sustained
if these drivers of behavior are not considered. A systems-oriented, multilevel framework
encompassing science and research capacity-building is the way to generate solutions
that deal with the complex system in which obesity arises. A multilevel research agenda
is cross-disciplinary, bringing together expertise in traditionally disparate fields
to pose cross-disciplinary hypotheses and to test those hypotheses collectively. The
agenda also would extend conventional research boundaries by tackling structural aspects
of the social, physical, and policy environment that affect obesity. Capacity building
for global research is critical for sustaining a multilevel research agenda for obesity
and chronic disease prevention.
Ultimately, interventions should strive to make healthy eating and physical activity
a natural and easy way of life. Using the framework discussed here, one approaches
the problem by first looking at the whole picture rather than immediately zeroing
in on a detail. Having a view, even if not a full understanding, of the relations
among factors that regulate energy balance, across individuals as well as populations,
allows one to simultaneously consider multiple leverage points in the system within
which obesity occurs that can or need to be modified to yield the desired outcomes
(52). Focused studies can then be designed to confirm and quantify these relationships
and to test their effects. By nature, this systems-oriented, multilevel approach is
solution-oriented, underlining the philosophy that mechanistic and intervention studies
are worthy only if they can improve population health in a sustainable way. Given
where we are today, faced with the continued lack of effective and sustainable prevention
strategies, there is a critical need to implement this multilevel approach. We can
do this by extending the boundaries of biomedical research to fill the gaps across
all the disciplines relevant to obesity, from biological and behavioral sciences to
social and policy research.