Objective: We conducted this systematic review to support the U.S. Preventive Services Task Force (USPSTF) in updating its 2012 recommendation on behavioral counseling to promote a healthful diet and physical activity for the primary prevention of cardiovascular disease (CVD) in adults without known CVD risk factors. Our review addressed four key questions: 1) Do primary care behavioral counseling interventions to improve diet, increase physical activity, and/or reduce sedentary behavior improve health outcomes in adults? 2) Do primary care behavioral counseling interventions to improve diet, increase physical activity, and/or reduce sedentary behavior improve intermediate outcomes associated with CVD in adults? 3) Do primary care behavioral counseling interventions to improve diet, increase physical activity, and/or reduce sedentary behavior improve associated health behaviors in adults? 4) What adverse events are associated with primary care behavioral counseling interventions to improve diet, increase physical activity, and/or reduce sedentary behavior in adults?
Data Sources: We performed a search of MEDLINE, PubMed (publisher-supplied), PsycINFO, and the Cochrane Central Register of Controlled Trials for studies published through May 25, 2016. Studies included in the 2010 USPSTF review were re-evaluated for potential inclusion. We supplemented searches by examining reference lists from related articles and expert recommendations and searched federal and international trial registries for ongoing trials.
Study Selection: Two researchers reviewed 10,045 titles and abstracts and 351 full-text articles against prespecified inclusion criteria. Eligible studies were those that evaluated the effectiveness of a behavioral intervention targeting improved diet, increased physical activity, decreased sedentary time, or a combination of these targets among adults without known hypertension, dyslipidemia, diabetes, impaired fasting glucose or glucose tolerance, or a combination of these factors. Studies among adults without these risk factors but with other characteristics that may still put them at elevated risk for CVD (e.g., being overweight or having obesity, having a family history of CVD or diabetes, having high-normal blood pressure) were included. Studies focused on the primary prevention of CVD among persons with traditional CVD risk factors or weight loss were excluded from this review, as they were the focus of other USPSTF reviews and recommendations. Studies that recruited participants from primary care or the broader health care system, took place in primary care or included primary care staff, or were deemed to be potentially feasible for primary care were eligible for inclusion. Studies had to take place in a developed country and be published in the English language to be included. We conducted dual independent critical appraisal of all provisionally included studies and abstracted all important study details and results from all studies rated fair or good quality. Data were abstracted by one reviewer and confirmed by another.
Data Analysis: Data on health outcomes and harms were sparsely reported, and the specific outcomes measured differed across trials, precluding meta-analysis, so we summarized those data in tables and narratively. For intermediate health outcomes and physical activity behavioral outcomes, we ran random effects meta-analyses using the DerSimonian and Laird method to calculate the pooled differences in mean changes (for continuous data) and pooled odds ratio (for binary data). We examined statistical heterogeneity among the pooled studies using standard chi-squared tests and estimated the proportion of total variability in point estimates using the I2 statistic. Meta-analyses for each dietary outcome found considerable statistical heterogeneity (I2>88%) that could not be adequately explained. Thus, we did not present the pooled estimates for these outcomes. We used meta-regression to explore potential effect modification by various study, population, and intervention characteristics, such as study quality, link to primary care, intervention focus, intervention intensity, and baseline characteristics. We generated funnel plots and conducted tests for small-study effects for all pooled analyses. Using established methods, we assessed the strength of evidence for each key question.
Results: We included 88 trials reported in 145 publications. We carried forward 50 trials from our previous review; 38 new trials were added. Of the 88 included trials, 12 reported health outcomes (KQ 1) (e.g., CVD events, self-reported quality of life), 34 reported intermediate health outcomes (KQ 2) (e.g., lipid, blood pressure, and glucose levels; weight measures), 86 reported behavioral outcomes (KQ 3) (i.e., objective or self-reported measures of diet, physical activity, or sedentary time), and 14 reported harms (or lack thereof) of a counseling intervention (KQ 4). The majority of the trials took place in the United States and were conducted within or recruited from a primary care setting. There was great diversity in the interventions that were tested; 23 trials focused on healthful diet and physical activity, another 24 on healthful diet only, and 44 on physical activity only. Intervention intensity (total minutes of contact) ranged from 3 to 2,340 minutes (39 hours), with a mean of 6 hours and 11 minutes. Low-intensity interventions were mostly mailed, print-based interventions, whereas medium- and high-intensity interventions involved one-on-one individual and telephone counseling and group sessions.
Health outcomes: Four trials (all in the original review) of high-intensity diet-only interventions reported no differences in all-cause or CVD-related mortality between intervention and control groups at 3 to 15 years of followup. Also, there were no consistent findings for the effects on CVD events over 8 to 15 years of followup. Results of 10 trials (mostly physical activity interventions) showed general improvements in quality of life over 6 to 12 months among intervention groups, but there was no consistent benefit of the intervention compared with control conditions.
Intermediate outcomes: There was evidence of small, statistically significant improvements in systolic blood pressure (mean difference [MD], −1.26 mm Hg [95% confidence interval (CI), −1.77 to −0.75]; k=22), diastolic blood pressure (MD, −0.49 mm Hg [95% CI, −0.82 to −0.16]; k=23), low-density lipoprotein cholesterol level (MD, −2.58 mg/dL [95% CI, −4.30 to −0.85]; k=13), and total cholesterol level (MD, −2.85 mg/dL [95% CI, −4.95 to −0.75]; k=19) at 6 to 12 months associated with healthful diet and/or physical activity interventions. For adiposity outcomes, interventions were associated with improvements in body mass index (MD, −0.41 kg/m2 [95% CI, −0.62 to −0.19]; k=20), weight (MD, −1.04 kg [95% CI, −1.56 to −0.13]; k=20), and waist circumference (MD, −1.19 cm [95% CI, −1.79 to −0.59]; k=17) although there was considerable statistical heterogeneity (I2 >90%) in all of these analyses, and therefore pooled results should be interpreted with caution. Very few studies reported the effects of the interventions beyond 12 months. There was evidence of a dose-response effect, with an association between increasing intervention intensity and larger improvements in intermediate outcomes, but insufficient evidence to assess the effects of low-intensity interventions alone on intermediate outcomes. There was no evidence of an association with high-density lipoprotein cholesterol, triglycerides, or fasting glucose level and limited evidence on the effects of interventions on incident hypertension, dyslipidemia, and diabetes.
Behavioral outcomes: There was consistent evidence that behavioral interventions generally improved participants’ dietary intake and physical activity levels at 6 to 12 months of followup. Between-group differences for dietary outcomes were in the magnitude of 65 kcal/day (favoring the control group) to −500 kcal/day (favoring the intervention group) in total energy intake (k=11), 0.8 to −11 percentage points in the percent of calories from fat (k=15), −0.3 to −4.1 percentage points in the percent of calories from saturated fat (k=9), and approximately −380 to nearly −1,400 mg/day of sodium (k=6). Effects on fruit and vegetable intake ranged from between-group differences of −0.2 servings/day (favoring the control group) to 2.2 servings/day (favoring the intervention group) (k=16); between-group differences in grams of fiber per day ranged from 1 to 2.5 g/day in favor of the intervention group (k=6). Persistent effects of the interventions were seen over time for all dietary outcomes among studies that reported multiple time points. Physical activity interventions (with or without dietary messages) resulted in an approximate 35-minute increase in physical activity per week compared with control groups (k=27). Additionally, intervention group participants had a 32-percent higher odds of meeting physical activity recommendations compared with those in the control group (k=16). Studies that limited enrollment to participants with suboptimal levels of physical activity at baseline (generally below the recommended level of 150 minutes/week) resulted in greater increases in physical activity compared with those that did not limit enrollment based on baseline physical activity levels. In contrast to findings for intermediate outcomes, there was no evidence of effect modification based on intervention intensity.
Adverse events: Across 14 trials, there were no serious adverse events related to counseling, although we did not hypothesize that these counseling interventions would result in serious harms (i.e., unexpected or unwanted medical attention). There was no consistent evidence that the incidence of injuries, falls, or adverse cardiovascular events were different among participants in physical activity interventions and those in control groups.
Limitations: Our focus on counseling interventions that take place in or were considered feasible for primary care among adults without risk factors for CVD or known CVD is relatively narrow. This systematic review represents only a subset of a much larger body of literature on diet and physical activity interventions. There was very limited evidence on the effectiveness of interventions aimed at reducing time spent in sedentary behaviors.
Conclusions: The results of our updated systematic review are generally consistent in magnitude with our 2010 review on this topic. In general, diet and physical activity behavioral interventions for generally unselected adults who were not targeted for counseling based on their CVD risk resulted in consistent modest benefits across a variety of important intermediate health outcomes, including blood pressure, low-density lipoprotein, and total cholesterol levels as well as adiposity, with evidence of a dose-response effect with higher intensity interventions resulting in greater improvements. Small-to-moderate improvements were also seen in dietary and physical activity behaviors. Very limited evidence exists on health outcomes or harmful effects of these interventions. The improvements we saw, however, in intermediate and behavioral health outcomes could translate into long-term reduction in CVD-related events, with minimal to no harms, if such changes were maintained over time.