Sustaining Health-Protective Behaviors Such as Physical Activity and Healthy Eating

The risk of many serious chronic health conditions, including coronary heart disease, type 2 diabetes, and cancer, can be substantially reduced by protective health behaviors, such as regular physical activity and healthy dietary intake. To attain significant health benefits, however, these health-protective behaviors should be performed consistently and regularly (ie, every day or multiple times per day or week). For example, the 2008 Physical Activity Guidelines for Americans recommend that adults should accumulate at least 150 minutes per week of moderate-intensity aerobic physical activity or 75 minutes per week of vigorous-intensity aerobic physical activity–preferably spread across the days of the week.¹ Furthermore, the 2015–2020 Dietary Guidelines for Americans recommends that adults should fill half their plate with fruits and vegetables at every meal and snacking occasion.²Formaximumhealth protection, physical activity and healthy dietary intake should become an integral part of an individual’s daily routine.

A defining characteristic of these repeated-occurrence health behaviors, which differentiates them from limited-occurrence health behaviors such as screenings and vaccinations, is that they should be performed on a regular basis over sustained periods of time. Ideally, behaviors should be maintained at this frequency across the entire lifespan. However, the amount of time, planning, effort, and resources needed to sustain regular physical activity and healthy dietary intake may be substantial. Therefore, it is not surprising that only a small proportion of US adults attain recommended levels of these behaviors at any given time (eg, 22% meet physical activity guidelines,³ and 12% meet guidelines for fruit and vegetable intake⁴).The percentage of adults who successfully maintain recommended physical activity and dietary intake levels across multiple decades of their lives is most likely much lower.

When the factors that influence health-protective behaviors vary over short time periods and across settings, maintaining consistency can be difficult.

Evidence is lacking on intervention strategies to maintain these health-protective behaviors over sustained periods of time. Intervention studies promoting physical activity and healthy eating typically focus on the initiation of these behaviors for periods shorter than 6 months among individuals who were not previously performing them. Even when successfully adopted, new patterns of behavior are not maintained over longer follow-up intervals and typically regress to baseline levels.⁵ There is limited evidence on how to help individuals avoid temporary lapses in behavior. Declines in healthy behaviors, even for short periods of time, can have negative health consequences and can increase vul-nerability to permanent failure to reengage in the behavior (ie, relapse).

Sustaining health-protective behaviors, such as physical activity and healthy eating over time, may be challenging due to daily and within-daily fluctuations in how people feel, persons with whom they interact, obstacles they encounter, and the environments in which they live and work. When the factors that influence health-protective behaviors vary over short time periods and across settings, maintaining consistency can be difficult.

Strategies to promote long-term engagement in health-protective behaviors may be informed by under-standing the microtemporal processes underlying these actions. Factors influencing physical activity and healthy eating may become more apparent when assessed on a microtimescale (ie, across minutes, hours, or days) because these behaviors are largely driven by temporal and situational cues such as location, social context, and affective and physical feelings that rapidly change over short time frames. However, to date, health behavior research has predominantly focused on macrotemporal processes that unfold over longer periods of time such as weeks, months, or years. Health behavior interventions and theories typically seek to understand between-person effects of time-invariant explanatory factors (eg, traits, long-standing attitudes and beliefs, sociodemographic characteristics) on behavior and do not address whether there are also within-person effects of time-varying explanatory factors on behavior.

Expanding health behavior research to address microtemporal processes has the potential to significantly inform health behavior maintenance and intervention strategies in several key ways. First, examining microtemporal processes could help address questions about the temporal specificity of factors influencing health behaviors. These types of questions aim to determine whether explanatory factors and behavior are temporally simultaneous, whether effects that pre-cede a behavior are stronger than effects that are consequences of a behavior, whether there are differences in the strength of effects across time (ie, time-varying effects), and whether degree of fluctuation (ie, consistency vs instability) in an explanatory factor predicts behavior. Examples include the following: (1) whether mood influences the likelihood of exercising to a greater extent than exercise influences mood; (2) at what time of day does mood have the strongest effect on the likelihood of exercising; and (3) whether individuals with less stable mood profiles are more likely to eat in unhealthy ways.

Second, research that investigates microtemporal processes also could address questions about the situational specificity of factors influencing health behaviors. These questions may ask under what combinations of conditions, contexts, or exposures (eg, environmental, affective, biological) do explanatory factors have the greatest effects on behavior (ie, time-varying moderators). For example, do people engage in more stress-induced eating when alone than when around other people?

Third, uncovering microtemporal processes underlying health behaviors also could help address questions about person specificity. These questions seek to determine what sets of factors are more predictive for which individuals. Microtemporal processes may unfold differently across people based on individual preferences, environments, and constraints. An assumption of most health behavior interventions is that a common set of factors explains the behaviors of most people. However, this approach may oversimplify underlying mechanisms and fail to adequately predict behavior for some people. Even when health behavior interventions are found to be effective, there is enormous variability in individual response. For example what factors influence why some people walk up and down escalators while others simply let the machine take them up or down. Specification in these domains could lead to more predictive models of health behavior, potentially offer a substantial shift in the way that health behavior interventions are developed, and follow recent calls from the National Institutes of Health (NIH) for precision approaches to medicine.⁶

Until recently, limitations in methods for collecting data (primarily retrospective assessments giving static snapshots of behavior) constrained what clinicians and researchers could observe. Fortunately, new methodologies are now available to collect and analyze the dynamic types of data needed to examine microtemporal processes that underlie health-protective behaviors. The recent increased availability of mobile and wearable smartphone and smartwatch technologies offers an important opportunity to obtain frequent and continuous assessments of health behaviors and determinants. These emerging technologies can unobtrusively collect large streams of subjective and objective data at the population level. When combined with machine learning or other exploratory data mining, analytic approaches could yield critical insights into the prediction and modeling of microtemporal mechanisms underlying health-protective behaviors. These discoveries are expected to form the basis of intensively adaptive interventions or just-in-time adaptive interventions⁷ which aim to deliver personalized behavior–change strategies under the conditions when they will be most effective to promote long-term maintenance of health-protective behaviors across months, years, and ideally decades.

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