Physical Activity Moving Toward Obesity Solutions: Workshop Summary (2015) / Chapter Skim
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1 Introduction
1 Introduction
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In 2008, the U.S. federal government for the first time issued fully approved physical activity guidelines.
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. This first chapter summarizes the welcoming remarks of Victor Dzau, president of the IOM at the time of the workshop and currently president of the newly formed National Academy of Medicine; Russell Pate's introductory presentation, which provided historical context for understanding the current state of the science regarding the impact of physical activity on the prevention and treatment of obesity; keynote speaker James Hill's presentation on the clarity of the evidence indicating that physical activity plays a significant role in reducing obesity; and Aviva Must's overview of sociodemographic disparities in obesity and physical activity as one of its determinants.
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, calls for physical activity to be an integral and routine part of life and for community planners, government officials, and others to work together to increase opportunities for and access to physical activities. The second, Educating the Student Body: Taking Physical Activity and Physical Education to School (IOM, 2013)
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Campaign; the Partnership for a Healthier America; the National Physical Activity Plan; and work by the President's Council on Fitness, Sports, and Nutrition. AN INTRODUCTION TO PHYSICAL ACTIVITY AND ITS IMPACT ON HEALTH AND WELL-BEING5 Walking is man's best medicine.
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. He also created what is known by many as the Paffenbarger curve, illustrating the relationship between physical activity and heart disease outcomes, with the low end of the activity continuum being associated with substantially elevated risks of fatal and nonfatal heart attacks (Paffenbarger et al., 1978)
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1978. Physical activity as an index of heart attack risk in college alumni.
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First, to study a construct, Pate said, scientists need to define it. Physical activity has been defined as "any bodily movement produced by skeletal muscles that results in energy expenditure." Pate underscored the importance of the "energy expenditure" component of that definition and remarked that the energy throughput impact of physical activity is a fundamental component of physical activity research.
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In Pate's opinion, the field achieved a new status when the large epidemiologic databases matured such that it became feasible to examine all-cause mortality as an outcome. As to why physical activity exerts its influence on health, Pate remarked that while scientists certainly have much to learn about underlying mechanisms, they know that acute exercise produces a profound physiologic response.
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Another approach is to think teleologically about how human bodies evolved to be what they were when humans were physically active huntergatherers. If the human body evolved to support a lifestyle that humans are no longer living, Pate said, "it should not be that surprising things don't always go well." A teleological approach to examining the issue of physical activity and health would suggest that the adaptations produced by regular participation in physical activity reflect a "reversion to the norm, not some odd behavior pattern.
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. For the remainder of his presentation, Hill described what scientists do and do not know about how adding or subtracting physical activity impacts the energy balance system.
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In sum, the scientific literature indicates that when physical activity is added to a weight loss program, the majority of people do not compensate, at least not completely. The net result is that adding physical activity produces a negative energy balance.
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In Hill's opinion, a fair amount of evidence suggests that most people do not immediately decrease their energy intake when they decrease their physical activity, suggesting that decreased physical activity is likely an important risk factor for weight gain. Active Regulation of Energy Balance In Hill's opinion, the greater question is not how physical activity affects energy expenditure or intake but how it affects the active regulation of energy balance (see Figure 1-2)
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If one were to conduct a study Physical Activity Threshold for Optimal Weight Regulation Energy Intake Body Weight "Unregulated" Zone " "Regulated" Zone PHYSICAL ACTIVITY FIGURE 1-3 A theoretical graph illustrating the active regulation of energy balance. NOTE: The dashed line represents energy intake as a function of physical activity level; the solid line represents body weight as a function of physical activity level.
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"Everything we know about the science of energy balance suggests that this trend is a risk factor for weight gain," he noted. According to Hill, every study conducted on highly palatable energy-dense diets combined with physical activity has shown less weight gain when physical activity was added to the diet compared with the diet alone.
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(People who occupy the regulated zone and who are able to match energy intake with energy expenditure are "pretty good compensators," Hill said, but they do not have a problem with excess body fat.) The bottom line, Hill concluded, is that everything known about the science of energy balance suggests that adding exercise has a positive effect on body fat mass.
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The scientific evidence around energy balance strongly suggests that increasing physical activity prevents weight gain and that decreasing physical activity promotes it. More important, Hill reiterated the importance of physical activity in moving people from the unregulated to the regulated zone.
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Finally, socially disadvantaged groups have reduced access to primary care and preventive services, so they may not receive information on physical activity's preventive health benefits. Must identified and went on to explore several key dimensions of both obesity and disparities in physical activity: race/ethnicity; disability; immigration status; socioeconomic status; geography (in terms of both where in the United States one lives and urban versus rural residence)
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Among adults, as with children, self-report data from the Behavioral Risk Factor Surveillance System (BRFSS) show very little racial/ethnic varia tion in physical activity, with low rates among all racial/ethnic groups.
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According to Must, qualitative studies have shown that, while norms in some Asian cultures do not support strenuous activity for girls, in other Asian cultures physical activity is very much a part of daily life and is viewed as being important to maintaining one's overall balance. Other qualitative work has shown that African American women often put the needs of others (particularly family members)
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In contrast and somewhat surprising, in Must's opinion, are self-report data from the National Survey of Children and Health (NSCH) showing that regular physical activity in children aged 6-17 years is greater among those who are U.S.-born with either one immigrant parent or two U.S.
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According to 2013 BRFSS data, the likelihood of an adult's meeting the national physical activity guidelines increases with income level. Must pointed out, however, that the percentage of adults meeting the guidelines is low across all income levels, with only 26 percent of people earning $75,000 or more meeting the nationally recommended levels of aerobic and muscle-strengthening physical activity.
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. In Must's opinion, public health practitioners can form strategic alliances with other public sectors to affect the built environment in ways that improve physical activity patterns for all inhabitants.
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INTRODUCTION 23 a) WA MT ME ND MN OR VT NH ID SD WI NY MA WY MI RI CT IA PA NE NJ NV OH DE UT IL IN CO WV MD KS VA DC CA MO KY NC TN OK AZ AR SC NM AL GA MS AK TX LA FL HI GUAM PR 15%–<20% 20%–<25% 25%–<30% 30%–<35% ≥35% Figure 1-6a b)
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. PANEL DISCUSSION To begin the panel discussion following Must's presentation, moderator Pate asked whether the "cut-off" point for physical activity between the regulated and unregulated zones, as described by Hill, is possibly or likely different for different demographic subgroups given some of the trends described by Must.
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'" Must called for a greater understanding of what she referred to as the physical activity version of making the healthy or natural choice. She wondered what could be learned from cultures in which physical activity is valued as something that keeps human beings "in balance."
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