Physical Activity Moving Toward Obesity Solutions: Workshop Summary (2015) / Chapter Skim
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3 Physical Activity and Primary Prevention of Obesity in Adults
3 Physical Activity and Primary Prevention of Obesity in Adults
Pages 43-56
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From page 43... ...
Ekelund described evidence showing only a very weak association between physical activity and weight gain and other evidence suggesting that physical activity reduces the risk of obesity, but only in people with normal weight status at baseline. In contrast, Ekelund continued, yet other evidence indicates a strong relationship between physical activity and other health outcomes, including all-cause mortality.
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From page 44... ...
Does Physical Activity Prevent Weight Gain? To measure the effect of physical activity on weight gain, epidemiologists measure physical activity at baseline, measure body weight at followup, and adjust for confounding factors, Ekelund explained.
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From page 45... ...
They concluded that physical activity at baseline did not predict weight gain at follow-up, but it did predict waist circumference in both men and women. However, the magnitude of the association with waist circumference was minor, Ekelund said, with the difference in gain over 5 years between the inactive and moderately inactive groups being only 0.05 cm.
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From page 46... ...
Ekelund concluded, "There may be differential associations between physical activity and weight gain depending on the initial BMI or body weight status." Is Change in Physical Activity Associated with Change in Body Weight? The simplest model used to determine whether a change in physical activity is associated with a change in body weight entails measuring both exposure (physical activity)
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From page 47... ...
." Ekelund interpreted these findings to mean that physical activity at baseline did not predict weight gain, but change in physical activity did. Reverse Causality: Does Weight Status Predict Physical Inactivity?
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From page 48... ...
The difference between being moderately inactive and inactive, Ekelund explained, was about 20 minutes of brisk walking per day, or 100 kilocalories expended in physical activity. Ekelund's take-home message was that physical activity prevents weight gain in a small segment of the population who are of normal weight and who are highly physically active, but the health benefits of physical activity are well established and indisputable.
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From page 49... ...
While Mayer's observations were limited by their cross-sectional nature, they nonetheless suggested that physical activity can prevent weight gain despite increasing energy intake. As James Hill had elaborated during his keynote presentation, Ross reminded the workshop audience how the mismatch between body weight and energy intake initially observed by Mayer and colleagues (1956)
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50 PHYSICAL ACTIVITY FIGURE 3-1 Body weight and caloric intake as a function of physical activity. SOURCE: Presented by Robert Ross on April 14, 2015 (reprinted with permission from Mayer et al.
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In a systematic review of interventions aimed at preventing weight gain in adults, Lombard and colleagues (2009) identified nine randomized controlled trials with intervention lengths varying from a few weeks to 5 years.
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They found significant weight gain prevention in the intervention groups. Most other trials of interventions to prevent weight gain have been successful in achieving that goal, according to Ross.
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From page 53... ...
Evidence from effectiveness studies suggests that lifestyle interventions designed to prevent weight gain are generally effective, although it is impossible to identify which aspects of such interventions -- diet and/or exercise -- are contributing to their success. Nor is there sufficient evidence to determine an ideal "dose" of exercise required to prevent weight gain.
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From page 54... ...
Ekelund added that it was important to keep in mind that almost all data obtained from observational research have been on body weight or BMI, and in some cases waist circumference. Very few large-scale epidemiologic studies have measured body composition.
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PHYSICAL ACTIVITY AND PRIMARY PREVENTION OF OBESITY IN ADULTS 55 viduals continue, after their trial has ended, to do what they were taught to do during the intervention to prevent weight gain. Ross remarked that participants do very well when they maintain contact with the interventionist.
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