RESEARCH AND PRACTICE
Images of a Healthy Worksite: A Group-Randomized Trial for Worksite Weight Gain Prevention With Employee Participation in Intervention Design I. Diana Fernandez, MD, PhD, MPH, Nancy P. Chin, PhD, MPH, Carol M. Devine, PhD, Ann M. Dozier, RN, PhD, Camille A. Martina, PhD, Scott McIntosh, PhD, MA, Kelly Thevenet-Morrison, MS, and Hongmei Yang, PhD
Sixty-eight percent of adults residing in the United States are overweight or obese,1 and these conditions affect more than 1.4 billion adults worldwide.2 Traditional obesity control strategies, which have focused on changing diet and physical activity (PA) behaviors, provide significant individual benefits3 but are considered insufficient to reduce population disease burdens,4,5 for which broad, population-based approaches are needed.6 In addition to individual biology and behaviors, the physical, social, and cultural environment appears to contribute to the upward trend in population estimates of overweight and obesity7,8 by facilitating high-energy, low-nutrient diets and reducing the need to be physically active to perform activities of daily life.9 Worksites are feasible self-contained environments with established communication systems in which interventions manipulating the food and PA environment and the social marketing of lifestyle changes can be implemented. Given that 58.4% of the US population aged 16 years or older is employed,10 worksite interventions have the potential to reach large number of adults11 and can foster the participation of employees in project development and sustainability.12---14 Moreover, participatory worksite interventions address workers’ needs, priorities, and interests and allow strategies to be adapted to the realities of individual sites.13 There is also a business case for weight control programs. In comparison with their nonobese counterparts, overweight and obese employees have higher absenteeism rates, have more work limitations, and are less productive.15---18 With these issues in mind, the National Heart, Lung, and Blood Institute developed the Obesity Prevention in the Worksite initiative, a population-based approach to promoting
Objectives. We assessed the effects of a worksite multiple-component intervention addressing diet and physical activity on employees’ mean body mass index (BMI) and the percentage of employees who were overweight or obese. Methods. This group-randomized trial (n = 3799) was conducted at 10 worksites in the northeastern United States. Worksites were paired and allocated into intervention and control conditions. Within- and between-groups changes in mean BMIs and in the percentage of overweight or obese employees were examined in a volunteer sample. Results. Within-group mean BMIs decreased by 0.54 kilograms per meter squared (P = .02) and 0.12 kilograms per meter squared (P = .73) at the intervention and control worksites, respectively, resulting in a difference in differences (DID) decrease of 0.42 kilograms per meter squared (P = .33). The within-group percentage of overweight or obese employees decreased by 3.7% (P = .07) at the intervention worksites and increased by 4.9% (P = .1) at the control worksites, resulting in a DID decline of 8.6% (P = .02). Conclusions. Our findings support a worksite population strategy that might eventually reduce the prevalence of overweight and obesity by minimizing environmental exposures to calorically dense foods and increasing exposures to opportunities for energy expenditure within worksite settings. (Am J Public Health. 2015;105:2167–2174. doi:10.2105/AJPH.2014.302397)
behavioral change through environmental interventions that address prevention and control of weight gain.19 Prior to this initiative, worksite trials were either limited scope interventions, targeting a few aspects of the food or PA environment,9,20---23 or broader scope efforts simultaneously targeting risk factors for cardiovascular disease and cancer (e.g., smoking, diet).24---28 In addition, few studies addressed environmental influences related to excessive weight gain. Here we report the results of Images of a Healthy Worksite, one of the studies that is part of the Obesity Prevention in the Worksite initiative; this comprehensive nutrition and PA intervention was designed to promote healthy lifestyles and to stop the shift to the right of the population body mass index (BMI) curve. In this study, worksites were designated to receive an environmental intervention, and
October 2015, Vol 105, No. 10 | American Journal of Public Health
employees participated in intervention design. We hypothesized that mean BMIs among employees at the intervention worksites and the percentages of employees who were overweight or obese would not increase over a 2-year period or would increase less than at control worksites.
METHODS The study, which consisted of 2 phases, was conducted from 2005 to 2010 at a nonunionized manufacturing, research, and development company with multiple sites in the northeastern United States. In phase 1, we collected qualitative data to gain a broad understanding of the social and cultural roles of food and PA among workers as well as to elicit workers’ perspectives on potential interventions that would be socially feasible and
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culturally acceptable.29 In phase 2, we conducted a nested group-randomized trial with a main effects design to assess changes in the worksite environment resulting from an intervention promoting healthy lifestyles through portion control, healthy diets, and PA. The unit of randomization and analysis was the worksite. We used a nested cross-sectional design to test the effects of the intervention on the entire worksite population as opposed to individual members as in a nested cohort design. Consequently, we assessed 2 cross-sectional samples of employees within worksites, one at baseline and another after the completion of the intervention. We enrolled 12 worksites and matched them a priori into pairs according to type of work (blue or white collar), because of suggested differences in blue- and white-collar employees’ responses to worksite interventions,30 and presence or absence of a cafeteria on the premises, which could have affected the implementation of our intervention. We ensured that all worksites were geographically and administratively independent of each other to avoid experimental contamination between worksites in different arms of the trial. Intervention allocation (within pairs) was achieved through simple randomization. After randomization and prior to our baseline assessments, the company was restructured, resulting in the closing of 3 participating worksites (one pair and one member of another pair). With the assistance of company collaborators, we identified a replacement worksite, resulting in a total of 5 matched pairs. Volunteer samples of full-time employees within worksites were eligible to participate in assessments if they were aged 18 years or older. There were no exclusions by BMI category or other chronic conditions because the intervention addressed small lifestyle changes that could be adopted regardless of any underlying conditions.
at team meetings during baseline data collection. During postintervention data collection, informational activities related to participant enrollment were more restricted. Study staff set up information desks for recruitment and assessments scheduled at different times and locations to accommodate employees and production schedules. Employees received a small incentive for enrollment ($4 cash value) and were eligible for cash drawings ($100) upon returning their surveys. Trained project staff took anthropometric measures and distributed surveys collecting information on demographic characteristics, diet and PA behaviors, and job-related characteristics at baseline and postintervention. Participants and project staff were unaware of worksite assignments at the baseline assessments. We used a Tanita electronic scale to measure employees’ weight (in kilograms) and a Shorr measuring board stadiometer to measure their height (to the nearest 0.1 cm) in street clothing and without shoes in a private place. We also gathered data on participants’ age, marital status, education, income, and smoking status. Because of potential race/ ethnicity-specific differences in participation in and responses to our intervention, participants were asked to categorize their race/ethnicity as one of the following: White, Black/African American, Native Hawaiian or Pacific Islander, Native American or Alaska Native, Asian, or Hispanic/Latino. Race was collapsed into White, African American, and other. We used the transtheoretical model to assess participants’ current stage of behavior change with respect to their diet and PA habits (precontemplation, contemplation, action, or maintenance).31 Items focusing on their confidence in changing their habits and the importance of doing so were scored from 0 to 10 (with lower scores indicating less confidence or importance). We used the Job Content Questionnaire32 to assess job insecurity and job demands associated with employees’ weight status.33,34
Recruitment and Data Collection Baseline and postintervention data were collected from February to October 2006 and January to June 2009, respectively. Interventions were implemented sequentially at each worksite after completion of the baseline assessments. Employees were informed of the study through e-mails, flyers, and presentations
Intervention We used the epidemiological triad adapted to obesity (employees’ biological and behavioral influences as the host, energy balance as the agent, and the obesogenic environment) as a model for understanding the problem of obesity from a population perspective and
2168 | Weight Control | Peer Reviewed | Fernandez et al.
identifying potential intervention sources.7 The goal of our intervention was to use social marketing strategies (e.g., demonstration events such as health fairs) to create a synergy between a worksite environment offering easy access to healthy choices and employees’ awareness of the connection of nutrition and PA behaviors with lifelong health and disease prevention.35 To develop intervention strategies tailored to each worksite and to build social support and employees’ capacity36 to address environmental contributors to weight gain, we formed employee advisory boards (EABs) including 5 to 10 employees from different levels of the company along with food service representatives, one of the study team members, and a group facilitator. Findings gleaned from phase 1 of the study and intervention strategies based on previous evidence were presented to each EAB for its input. EAB members surveyed their coworkers on the content of feasible interventions, and potential intervention strategies from all sources were compiled. A criterion selection matrix37 with a 5-point scale (on which lower scores indicated less importance) for each criterion (ease of implementation, potential employee participation, potential employee reach, probable acceptance by employees, cost to employee, and cost to project) was used to make decisions on potential interventions. Interventions with the highest scores were identified for implementation, and those with midrange scores were further discussed with the EABs for possible later implementation. The final intervention plan included common strategies for all worksites designed by the research team based on previous studies and worksite-specific strategies planned by the EABs on the basis of the selection matrix. The intervention strategies are presented according to epidemiological triad component and whether they were initiated by the research team or the employees. The following intervention strategies were initiated by the research team to increase employee awareness and build capacity: d
Awareness workshops conducted at different times to accommodate shift work (e.g., “Packing a Healthy Lunch,” “The Optimal Workout”);
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RESEARCH AND PRACTICE
d
d
d
d
d
d
d
d
Brochures on nutrition and PA (e.g., “Grocery Store Grab Bag,” “Stretching at the Workplace”); “Make the Right Choice” stickers placed on vending machines; Monthly newsletters with information on upcoming events, monthly recipes, and topic of the month; Healthy beverage signs; Monthly cafeteria nutrition promotions (e.g., taste tasting of whole grains and lowsodium soup, how to save 100 calories a day); Educational posters on wellness and tear-off table tents in common areas (e.g., “Portion Puzzles,” “Look to the Label,” “Dips and Sauces”); Website with wellness information, walking route maps, a member’s forum, and a chat session with a dietitian; and Taste testing of low-fat and no-fat salad dressings.
The following intervention strategies were initiated by the EABs to increase employee awareness and build capacity:
d
The following intervention strategies were initiated by the EABs to reduce energy intake and increase energy expenditure: d
d
d
d
d
d
d
d
d
d
d
d
Awareness workshops (e.g., “Healthy Holiday Eating,” “Find Time for Fitness”); Orientations at worksite gyms (2 worksites, implemented by research staff); Wellness books for worksite library (1 worksite); Bioimpedance scale for self-monitoring (1 worksite); “You’ve Been Caught” promotion (distribution of cards to employees making a healthy choice while at work) (1 worksite); and Health and wellness fairs on diet and nutrition, obesity, stress, cardiovascular disease, smoking risks, and PA (2 worksites).
The following intervention strategies were initiated by the research team to reduce energy intake and increase energy expenditure: d
d
d
d
Mapping and promotion of indoor and outdoor walking routes; Signs promoting stairway use; Chef training workshop (led by a registered dietitian) focusing on healthy cooking and identifying main dishes to offer in half portions; “Buy 3, Get 1 Free” punch cards (equivalent to a 40% price reduction per purchase)
Outdoor power walks (2 worksites); Treadmills and elliptical machines (1 worksite); Larger room to improve fitness facilities (1 worksite); Competitions on team fitness with pedometers, Frisbee golf, or bocce tournaments (1 worksite); “Veggie Bar Thursday” (1 worksite); Fruit basket deliveries to night shift employees; and Inclusion of healthy items in vending machines accompanied by taste testing (1 worksite without a cafeteria).
Finally, the following interventions were initiated by the research team to support a healthy worksite environment: d
d
promoting half portions, healthy entrees, and fruits and vegetables; and Promotion of healthy snack purchases from vending machines with stickers (‘buy 3, get 1 free’) redeemable for a free snack.
d
d
Support and promotion of environmental changes and new policies initiated by the company (e.g., farmer’s market, free gym); Social support for healthy lifestyles through the implementation of EABs in each intervention building; and Commitment of worksite food contractors in planning, policy, and intervention implementation.
Statistical Analysis Our primary and secondary outcomes were changes in average worksite BMIs (weight in kilograms divided by the square of height in meters) and the proportion of employees who were overweight or obese (BMI of ‡ 25), respectively. We first examined within-group changes in outcomes over time (e.g., changes in BMI from baseline to postintervention). The difference in differences (DID) in average worksite BMIs and in the percentage of employees who were overweight or obese was used to assess intervention effects. The 2 cases in which BMIs were plus or minus 3 standard deviations from the mean were considered outliers and were excluded from our analyses.
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Our analyses were conducted in accord with the intention to treat principle, which allowed us to appropriately infer the effects of instituting environmental interventions on the outcomes of interest regardless of worksite compliance. Worksites were matched a priori to ensure balance between the intervention and control conditions according to worksite characteristics, as opposed to a test of whether intervention effects were different across strata (pairs) defined by group characteristics. Therefore, we conducted an unmatched analysis. To test our primary hypothesis regarding changes in mean BMIs, we used a linear mixed effects model to conduct both unadjusted and adjusted time by condition analyses. In addition to the fixed effects of condition, time, and their interaction, each model included 3 random effects to account for positive intraclass correlations (one for correlation among employees within a worksite, one for correlation among employees within time by worksite survey, and one for random variation among employees). In the adjusted analysis, we controlled for unbalanced covariates between arms (P < .1) at baseline or postintervention resulting from the cross-sectional nature of the nested design; another reason for this strategy was to avoid confounding or reduced power.38 To test our secondary hypothesis regarding changes in overweight or obesity, we similarly conducted unadjusted and adjusted analyses by logistic mixed models to assess the effects of time, condition, and their interaction on the odds of overweight and obesity. We used density plots to graph the study population BMI distribution at baseline and postintervention by study arm. The trial was designed to have (1) 80% power to detect a minimum difference of 0.8 BMI units (SD = 5.0) over 2 years39,40 at a significance level of .05, (2) an over-time correlation of 0.5, and (3) an intraclass correlation coefficient below 0.0005 with clusters of unequal sample size.38,41 We used SAS/STAT version 9.2 (SAS Institute Inc, Cary, NC) to conduct all of our analyses.
RESULTS The study worksite and participant flowchart is shown in Figure 1. Five pairs of
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Worksites – 6 Pairs
Received Allocated Control Condition = 5
Total Workforce = 4470 Cross-Sectional Sample Mean Worksite Size = 890 Employees Range: 90 – 1319 n = 1547 Employees
Total Workforce = 3630 Cross-Sectional Sample Mean Worksite Size = 955 Employees Range: 214–1498 n = 1068 Employees
Total Workforce = 3557 Cross-Sectional Sample Mean Worksite Size = 793 Employees Range: 89 – 1052 n = 839 Employees
Total Workforce = 2657 Cross-Sectional Sample Mean Worksite Size = 576 Employees Range: 157–915 n = 345 Employees
Analysis
Received Allocated Intervention Condition = 5
Baseline Assessment
Randomized Within 5 Pairs
Follow-Up Assessment
Allocation
Enrollment
Lost 1 pair because of company restructuring
Worksite Analyzed = 5 Participants = 2386 Unadjusted Analysis Excluded = 1 - Outlying BMI 4 - Missing Height and Weight Participants Analyzed = 2381
Worksite Analyzed = 5 Participants = 1413 Unadjusted Analysis Excluded = 1 - Outlying BMI
Adjusted Analysis Excluded = 247 - Survey Nonresponse (10%) 252 - Missing Values on Covariates (11%) 1882 - Participants Analyzed
Adjusted Analysis Excluded = 224 - Survey Nonresponse (15%) 74 - Missing Values on Covariates (6%) 1114 - Participants Analyzed
Participants Analyzed = 1412
Note. BMI = body mass index.
FIGURE 1—Images of a Healthy Worksite study flowchart.
worksites remained in the study throughout. Because this was an environmental intervention, all employees at the intervention worksites were exposed to the intended treatment. A total of 3799 employees were assessed at the baseline and postintervention points. The intervention and control arms were unbalanced at baseline or postintervention (or both) with respect to job insecurity, job demand, education, income, race, gender, and some of the stages of change measures (Table 1). The participants were mostly middle aged, male, and highly educated, with earnings of more than $60 000 a year and a mean BMI
in the overweight category. The characteristics of the cross-sectional samples at baseline and postintervention by study arm were relatively similar with a few exceptions (e.g., the percentages of African American and female employees were higher in the control group than in the intervention group at the postintervention point). Model-fitting parameters showed an intraclass correlation coefficient of 0 for the response variable (BMI).
Effects on Mean Body Mass Index The within-group mean BMI decreased significantly at the intervention worksites after 2 years of the intervention (by 0.51 kg/m2; P = .03)
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and decreased nonsignificantly at the control worksites (by 0.20 kg/m2; P = .6; Table 2). The DID analysis showed the expected results (a decrease of 0.31 kg/m2; P = .46). The adjusted analysis revealed the same trends in withinworksite mean BMI changes (decreases of 0.54 kg/m2; P = .02, and 0.12 kg/m2; P = .73, at the intervention and control worksites, respectively) and a larger DID result in the expected direction (a decrease of 0.42 kg/m2; P = .33).
Effects on Percentages of Overweight or Obese Employees The unadjusted model showed that, within groups, the percentage of overweight or obese employees decreased over time at intervention worksites (by 4.5%; P = .02) and increased at control worksites (by 3.3%; P = .23). The DID between-arms results favored the intervention worksites (a decrease of 7.8%;, P = .02). In the adjusted model, within-worksite changes in the percentage of overweight or obese employees were of a different magnitude but remained in the same direction (decreases of 3.7%; P = .07, and increases of 4.9%; P = .1, at the intervention and control worksites, respectively), resulting in a net difference of 8.6% favoring the intervention in the DID analysis (P = .02).
Body Mass Index Distribution by Time and Condition At the intervention worksites, the curve of the adjusted BMI distribution shifted to the left between the baseline and postintervention points and was narrower to the expense of the right tail of the distribution (Figure 2). The area under the curve for BMIs below 24.9 (corresponding to healthy weight categories) was larger at postintervention. At the control worksites, the baseline and postintervention curves practically overlapped.
DISCUSSION The Images of a Healthy Worksite study was a worksite-randomized trial that tested environmental interventions targeting prevention of weight gain. A distinctive feature of this study was the participation of EABs that included company employees. Our results suggest that, after 2 intervention years, there was a favorable trend toward a larger decline in
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TABLE 1—Characteristics of the Cross-Sectional Samples (Baseline and Postintervention), by Study Arm: Images of a Healthy Worksite Study, 2005–2010 Baseline
Postintervention
Intervention Group (n = 1547), Mean 6SD or No. (%)
Control Group (n = 1067), Mean 6SD or No. (%)
P
Age, y
47.7 67.47
47.4 67.84
BMI, kg/m2
28.6 65.50
28.6 65.55
7.2 62.67
Psychological job demand scoreb BMI categoryc
Characteristic
Job insecurity scorea
Intervention Group (n = 839), Mean 6SD or No. (%)
Control Group (n = 345), Mean 6SD or No. (%)
P
.51
49 67.82
49.7 68.17
.18
.85
28.2 65.50
28.7 65.57
.75
7.3 63.32
.01
7.4 63.75
7.1 66.09
.02
31.9 68.72
32.5 610.81
.6
31.5 612.16
31.2 619.89
.78
.3
.03
1544 (100)
1068 (100)
837 (100)
344 (100)
Healthy weight
392 (25.4)
297 (27.8)
246 (29.4)
76 (22.0)
Overweight
631 (40.8)
407 (38.1)
354 (42.1)
153 (44.4)
Obese
521 (33.7)
364 (34.1)
237 (28.3)
115 (33.6)
1403 (100)
887 (100)
718 (100)
273 (100)
Secondary or less
241 (17.2)
201 (22.7)
131 (18.3)
74 (27.1)
College or less
882 (62.9)
561 (63.4)
454 (63.2)
165 (60.4)
Graduate level
280 (20.0)
124 (14.0)
133 (18.5)
34 (12.5)
1251 (100)
766 (100)
607 (100)
223 (100)
335 (26.8)
237 (30.9)
169 (27.8)
77 (34.2)
438 (72.2)
146 (65.5)
Educationc
Income, $c < 60 000 ‡ 60 000
916 (73.2)
529 (69.1)
1401 (100)
883 (100)
1285 (91.7)
African American Other
Racec
< .001
.04
.06
725 (100)
273 (100)
790 (89.5)
655 (90.3)
239 (87.6)
63 (4.5)
42 (4.8)
33 (4.6)
26 (9.5)
53 (3.8)
51 (5.8)
37 (5.1)
8 (2.9)
Genderc
1547 (100)
1068 (100)
838 (100)
345 (100)
Male
1054 (68.1)
594 (55.6)
493 (58.8)
216 (62.6)
493 (31.9)
474(44.4)
345 (41.2)
129 (37.4)
Importance of changing diet habits in the next 30 days (positive response)c
818 (58.5)
601 (66.3)
.001
401 (55.2)
163 (58.4)
.36
Confidence in changing diet habits in the next 30 days (positive response)c
981 (70.6)
675 (75.2)
.02
517 (72.2)
207 (76.7)
.16
Importance of changing PA habits in the next 30 days (positive response)c
832 (61.4)
623 (70.5)
< .001
412 (59.5)
180 (68.4)
.01
Confidence in changing PA habits in the next 30 days (positive response)c
996 (72.3)
670 (75.5)
.09
500 (71.4)
210 (78.4)
.03
1402 (100)
907 (100)
< .001
725 (100)
280 (100)
.01
Precontemplation
107 (7.6)
49 (5.4)
47 (6.5)
15 (5.4)
Contemplation
335 (23.9)
230 (25.4)
134 (18.5)
36 (12.9)
Action
111 (7.9)
112 (12.4)
56 (7.7)
38 (13.6)
Maintenance
849 (60.6)
516 (56.9)
488 (67.3)
191 (68.2)
1400 (100)
907 (100)
725 (100)
280 (100)
50 (3.6)
22 (2.4)
23 (3.2)
8 (2.9)
145 (10.4)
120 (13.3)
62 (8.6)
33 (11.8)
75 (5.4)
58 (6.4)
34 (4.7)
15 (5.4)
1130 (80.7)
707 (77.0)
606 (83.6)
224 (80.0)
Stage of change: PAc
1402 (100)
906 (100)
726 (100)
278 (100)
Precontemplation
95 (6.8)
51 (5.6)
45 (6.2)
21 (7.6)
Contemplation
472 (33.7)
370 (40.8)
210 (28.9)
91 (32.7)
Action
200 (14.3)
120 (13.3)
109 (15.0)
46 (16.6)
Maintenance
635 (45.3)
365 (40.3)
362 (49.9)
120 (43.2)
White
Female
Stage of change: fruit consumptionc
Stage of change: vegetable consumptionc Precontemplation Contemplation Action Maintenance
.08
.002
Images of a Healthy Worksite: A Group-Randomized Trial for Worksite Weight Gain Prevention With Employee Participation in Intervention Design I. Diana Fernandez, MD, PhD, MPH, Nancy P. Chin, PhD, MPH, Carol M. Devine, PhD, Ann M. Dozier, RN, PhD, Camille A. Martina, PhD, Scott McIntosh, PhD, MA, Kelly Thevenet-Morrison, MS, and Hongmei Yang, PhD
Sixty-eight percent of adults residing in the United States are overweight or obese,1 and these conditions affect more than 1.4 billion adults worldwide.2 Traditional obesity control strategies, which have focused on changing diet and physical activity (PA) behaviors, provide significant individual benefits3 but are considered insufficient to reduce population disease burdens,4,5 for which broad, population-based approaches are needed.6 In addition to individual biology and behaviors, the physical, social, and cultural environment appears to contribute to the upward trend in population estimates of overweight and obesity7,8 by facilitating high-energy, low-nutrient diets and reducing the need to be physically active to perform activities of daily life.9 Worksites are feasible self-contained environments with established communication systems in which interventions manipulating the food and PA environment and the social marketing of lifestyle changes can be implemented. Given that 58.4% of the US population aged 16 years or older is employed,10 worksite interventions have the potential to reach large number of adults11 and can foster the participation of employees in project development and sustainability.12---14 Moreover, participatory worksite interventions address workers’ needs, priorities, and interests and allow strategies to be adapted to the realities of individual sites.13 There is also a business case for weight control programs. In comparison with their nonobese counterparts, overweight and obese employees have higher absenteeism rates, have more work limitations, and are less productive.15---18 With these issues in mind, the National Heart, Lung, and Blood Institute developed the Obesity Prevention in the Worksite initiative, a population-based approach to promoting
Objectives. We assessed the effects of a worksite multiple-component intervention addressing diet and physical activity on employees’ mean body mass index (BMI) and the percentage of employees who were overweight or obese. Methods. This group-randomized trial (n = 3799) was conducted at 10 worksites in the northeastern United States. Worksites were paired and allocated into intervention and control conditions. Within- and between-groups changes in mean BMIs and in the percentage of overweight or obese employees were examined in a volunteer sample. Results. Within-group mean BMIs decreased by 0.54 kilograms per meter squared (P = .02) and 0.12 kilograms per meter squared (P = .73) at the intervention and control worksites, respectively, resulting in a difference in differences (DID) decrease of 0.42 kilograms per meter squared (P = .33). The within-group percentage of overweight or obese employees decreased by 3.7% (P = .07) at the intervention worksites and increased by 4.9% (P = .1) at the control worksites, resulting in a DID decline of 8.6% (P = .02). Conclusions. Our findings support a worksite population strategy that might eventually reduce the prevalence of overweight and obesity by minimizing environmental exposures to calorically dense foods and increasing exposures to opportunities for energy expenditure within worksite settings. (Am J Public Health. 2015;105:2167–2174. doi:10.2105/AJPH.2014.302397)
behavioral change through environmental interventions that address prevention and control of weight gain.19 Prior to this initiative, worksite trials were either limited scope interventions, targeting a few aspects of the food or PA environment,9,20---23 or broader scope efforts simultaneously targeting risk factors for cardiovascular disease and cancer (e.g., smoking, diet).24---28 In addition, few studies addressed environmental influences related to excessive weight gain. Here we report the results of Images of a Healthy Worksite, one of the studies that is part of the Obesity Prevention in the Worksite initiative; this comprehensive nutrition and PA intervention was designed to promote healthy lifestyles and to stop the shift to the right of the population body mass index (BMI) curve. In this study, worksites were designated to receive an environmental intervention, and
October 2015, Vol 105, No. 10 | American Journal of Public Health
employees participated in intervention design. We hypothesized that mean BMIs among employees at the intervention worksites and the percentages of employees who were overweight or obese would not increase over a 2-year period or would increase less than at control worksites.
METHODS The study, which consisted of 2 phases, was conducted from 2005 to 2010 at a nonunionized manufacturing, research, and development company with multiple sites in the northeastern United States. In phase 1, we collected qualitative data to gain a broad understanding of the social and cultural roles of food and PA among workers as well as to elicit workers’ perspectives on potential interventions that would be socially feasible and
Fernandez et al. | Peer Reviewed | Weight Control | 2167
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culturally acceptable.29 In phase 2, we conducted a nested group-randomized trial with a main effects design to assess changes in the worksite environment resulting from an intervention promoting healthy lifestyles through portion control, healthy diets, and PA. The unit of randomization and analysis was the worksite. We used a nested cross-sectional design to test the effects of the intervention on the entire worksite population as opposed to individual members as in a nested cohort design. Consequently, we assessed 2 cross-sectional samples of employees within worksites, one at baseline and another after the completion of the intervention. We enrolled 12 worksites and matched them a priori into pairs according to type of work (blue or white collar), because of suggested differences in blue- and white-collar employees’ responses to worksite interventions,30 and presence or absence of a cafeteria on the premises, which could have affected the implementation of our intervention. We ensured that all worksites were geographically and administratively independent of each other to avoid experimental contamination between worksites in different arms of the trial. Intervention allocation (within pairs) was achieved through simple randomization. After randomization and prior to our baseline assessments, the company was restructured, resulting in the closing of 3 participating worksites (one pair and one member of another pair). With the assistance of company collaborators, we identified a replacement worksite, resulting in a total of 5 matched pairs. Volunteer samples of full-time employees within worksites were eligible to participate in assessments if they were aged 18 years or older. There were no exclusions by BMI category or other chronic conditions because the intervention addressed small lifestyle changes that could be adopted regardless of any underlying conditions.
at team meetings during baseline data collection. During postintervention data collection, informational activities related to participant enrollment were more restricted. Study staff set up information desks for recruitment and assessments scheduled at different times and locations to accommodate employees and production schedules. Employees received a small incentive for enrollment ($4 cash value) and were eligible for cash drawings ($100) upon returning their surveys. Trained project staff took anthropometric measures and distributed surveys collecting information on demographic characteristics, diet and PA behaviors, and job-related characteristics at baseline and postintervention. Participants and project staff were unaware of worksite assignments at the baseline assessments. We used a Tanita electronic scale to measure employees’ weight (in kilograms) and a Shorr measuring board stadiometer to measure their height (to the nearest 0.1 cm) in street clothing and without shoes in a private place. We also gathered data on participants’ age, marital status, education, income, and smoking status. Because of potential race/ ethnicity-specific differences in participation in and responses to our intervention, participants were asked to categorize their race/ethnicity as one of the following: White, Black/African American, Native Hawaiian or Pacific Islander, Native American or Alaska Native, Asian, or Hispanic/Latino. Race was collapsed into White, African American, and other. We used the transtheoretical model to assess participants’ current stage of behavior change with respect to their diet and PA habits (precontemplation, contemplation, action, or maintenance).31 Items focusing on their confidence in changing their habits and the importance of doing so were scored from 0 to 10 (with lower scores indicating less confidence or importance). We used the Job Content Questionnaire32 to assess job insecurity and job demands associated with employees’ weight status.33,34
Recruitment and Data Collection Baseline and postintervention data were collected from February to October 2006 and January to June 2009, respectively. Interventions were implemented sequentially at each worksite after completion of the baseline assessments. Employees were informed of the study through e-mails, flyers, and presentations
Intervention We used the epidemiological triad adapted to obesity (employees’ biological and behavioral influences as the host, energy balance as the agent, and the obesogenic environment) as a model for understanding the problem of obesity from a population perspective and
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identifying potential intervention sources.7 The goal of our intervention was to use social marketing strategies (e.g., demonstration events such as health fairs) to create a synergy between a worksite environment offering easy access to healthy choices and employees’ awareness of the connection of nutrition and PA behaviors with lifelong health and disease prevention.35 To develop intervention strategies tailored to each worksite and to build social support and employees’ capacity36 to address environmental contributors to weight gain, we formed employee advisory boards (EABs) including 5 to 10 employees from different levels of the company along with food service representatives, one of the study team members, and a group facilitator. Findings gleaned from phase 1 of the study and intervention strategies based on previous evidence were presented to each EAB for its input. EAB members surveyed their coworkers on the content of feasible interventions, and potential intervention strategies from all sources were compiled. A criterion selection matrix37 with a 5-point scale (on which lower scores indicated less importance) for each criterion (ease of implementation, potential employee participation, potential employee reach, probable acceptance by employees, cost to employee, and cost to project) was used to make decisions on potential interventions. Interventions with the highest scores were identified for implementation, and those with midrange scores were further discussed with the EABs for possible later implementation. The final intervention plan included common strategies for all worksites designed by the research team based on previous studies and worksite-specific strategies planned by the EABs on the basis of the selection matrix. The intervention strategies are presented according to epidemiological triad component and whether they were initiated by the research team or the employees. The following intervention strategies were initiated by the research team to increase employee awareness and build capacity: d
Awareness workshops conducted at different times to accommodate shift work (e.g., “Packing a Healthy Lunch,” “The Optimal Workout”);
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d
d
d
d
d
d
d
d
Brochures on nutrition and PA (e.g., “Grocery Store Grab Bag,” “Stretching at the Workplace”); “Make the Right Choice” stickers placed on vending machines; Monthly newsletters with information on upcoming events, monthly recipes, and topic of the month; Healthy beverage signs; Monthly cafeteria nutrition promotions (e.g., taste tasting of whole grains and lowsodium soup, how to save 100 calories a day); Educational posters on wellness and tear-off table tents in common areas (e.g., “Portion Puzzles,” “Look to the Label,” “Dips and Sauces”); Website with wellness information, walking route maps, a member’s forum, and a chat session with a dietitian; and Taste testing of low-fat and no-fat salad dressings.
The following intervention strategies were initiated by the EABs to increase employee awareness and build capacity:
d
The following intervention strategies were initiated by the EABs to reduce energy intake and increase energy expenditure: d
d
d
d
d
d
d
d
d
d
d
d
Awareness workshops (e.g., “Healthy Holiday Eating,” “Find Time for Fitness”); Orientations at worksite gyms (2 worksites, implemented by research staff); Wellness books for worksite library (1 worksite); Bioimpedance scale for self-monitoring (1 worksite); “You’ve Been Caught” promotion (distribution of cards to employees making a healthy choice while at work) (1 worksite); and Health and wellness fairs on diet and nutrition, obesity, stress, cardiovascular disease, smoking risks, and PA (2 worksites).
The following intervention strategies were initiated by the research team to reduce energy intake and increase energy expenditure: d
d
d
d
Mapping and promotion of indoor and outdoor walking routes; Signs promoting stairway use; Chef training workshop (led by a registered dietitian) focusing on healthy cooking and identifying main dishes to offer in half portions; “Buy 3, Get 1 Free” punch cards (equivalent to a 40% price reduction per purchase)
Outdoor power walks (2 worksites); Treadmills and elliptical machines (1 worksite); Larger room to improve fitness facilities (1 worksite); Competitions on team fitness with pedometers, Frisbee golf, or bocce tournaments (1 worksite); “Veggie Bar Thursday” (1 worksite); Fruit basket deliveries to night shift employees; and Inclusion of healthy items in vending machines accompanied by taste testing (1 worksite without a cafeteria).
Finally, the following interventions were initiated by the research team to support a healthy worksite environment: d
d
promoting half portions, healthy entrees, and fruits and vegetables; and Promotion of healthy snack purchases from vending machines with stickers (‘buy 3, get 1 free’) redeemable for a free snack.
d
d
Support and promotion of environmental changes and new policies initiated by the company (e.g., farmer’s market, free gym); Social support for healthy lifestyles through the implementation of EABs in each intervention building; and Commitment of worksite food contractors in planning, policy, and intervention implementation.
Statistical Analysis Our primary and secondary outcomes were changes in average worksite BMIs (weight in kilograms divided by the square of height in meters) and the proportion of employees who were overweight or obese (BMI of ‡ 25), respectively. We first examined within-group changes in outcomes over time (e.g., changes in BMI from baseline to postintervention). The difference in differences (DID) in average worksite BMIs and in the percentage of employees who were overweight or obese was used to assess intervention effects. The 2 cases in which BMIs were plus or minus 3 standard deviations from the mean were considered outliers and were excluded from our analyses.
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Our analyses were conducted in accord with the intention to treat principle, which allowed us to appropriately infer the effects of instituting environmental interventions on the outcomes of interest regardless of worksite compliance. Worksites were matched a priori to ensure balance between the intervention and control conditions according to worksite characteristics, as opposed to a test of whether intervention effects were different across strata (pairs) defined by group characteristics. Therefore, we conducted an unmatched analysis. To test our primary hypothesis regarding changes in mean BMIs, we used a linear mixed effects model to conduct both unadjusted and adjusted time by condition analyses. In addition to the fixed effects of condition, time, and their interaction, each model included 3 random effects to account for positive intraclass correlations (one for correlation among employees within a worksite, one for correlation among employees within time by worksite survey, and one for random variation among employees). In the adjusted analysis, we controlled for unbalanced covariates between arms (P < .1) at baseline or postintervention resulting from the cross-sectional nature of the nested design; another reason for this strategy was to avoid confounding or reduced power.38 To test our secondary hypothesis regarding changes in overweight or obesity, we similarly conducted unadjusted and adjusted analyses by logistic mixed models to assess the effects of time, condition, and their interaction on the odds of overweight and obesity. We used density plots to graph the study population BMI distribution at baseline and postintervention by study arm. The trial was designed to have (1) 80% power to detect a minimum difference of 0.8 BMI units (SD = 5.0) over 2 years39,40 at a significance level of .05, (2) an over-time correlation of 0.5, and (3) an intraclass correlation coefficient below 0.0005 with clusters of unequal sample size.38,41 We used SAS/STAT version 9.2 (SAS Institute Inc, Cary, NC) to conduct all of our analyses.
RESULTS The study worksite and participant flowchart is shown in Figure 1. Five pairs of
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Worksites – 6 Pairs
Received Allocated Control Condition = 5
Total Workforce = 4470 Cross-Sectional Sample Mean Worksite Size = 890 Employees Range: 90 – 1319 n = 1547 Employees
Total Workforce = 3630 Cross-Sectional Sample Mean Worksite Size = 955 Employees Range: 214–1498 n = 1068 Employees
Total Workforce = 3557 Cross-Sectional Sample Mean Worksite Size = 793 Employees Range: 89 – 1052 n = 839 Employees
Total Workforce = 2657 Cross-Sectional Sample Mean Worksite Size = 576 Employees Range: 157–915 n = 345 Employees
Analysis
Received Allocated Intervention Condition = 5
Baseline Assessment
Randomized Within 5 Pairs
Follow-Up Assessment
Allocation
Enrollment
Lost 1 pair because of company restructuring
Worksite Analyzed = 5 Participants = 2386 Unadjusted Analysis Excluded = 1 - Outlying BMI 4 - Missing Height and Weight Participants Analyzed = 2381
Worksite Analyzed = 5 Participants = 1413 Unadjusted Analysis Excluded = 1 - Outlying BMI
Adjusted Analysis Excluded = 247 - Survey Nonresponse (10%) 252 - Missing Values on Covariates (11%) 1882 - Participants Analyzed
Adjusted Analysis Excluded = 224 - Survey Nonresponse (15%) 74 - Missing Values on Covariates (6%) 1114 - Participants Analyzed
Participants Analyzed = 1412
Note. BMI = body mass index.
FIGURE 1—Images of a Healthy Worksite study flowchart.
worksites remained in the study throughout. Because this was an environmental intervention, all employees at the intervention worksites were exposed to the intended treatment. A total of 3799 employees were assessed at the baseline and postintervention points. The intervention and control arms were unbalanced at baseline or postintervention (or both) with respect to job insecurity, job demand, education, income, race, gender, and some of the stages of change measures (Table 1). The participants were mostly middle aged, male, and highly educated, with earnings of more than $60 000 a year and a mean BMI
in the overweight category. The characteristics of the cross-sectional samples at baseline and postintervention by study arm were relatively similar with a few exceptions (e.g., the percentages of African American and female employees were higher in the control group than in the intervention group at the postintervention point). Model-fitting parameters showed an intraclass correlation coefficient of 0 for the response variable (BMI).
Effects on Mean Body Mass Index The within-group mean BMI decreased significantly at the intervention worksites after 2 years of the intervention (by 0.51 kg/m2; P = .03)
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and decreased nonsignificantly at the control worksites (by 0.20 kg/m2; P = .6; Table 2). The DID analysis showed the expected results (a decrease of 0.31 kg/m2; P = .46). The adjusted analysis revealed the same trends in withinworksite mean BMI changes (decreases of 0.54 kg/m2; P = .02, and 0.12 kg/m2; P = .73, at the intervention and control worksites, respectively) and a larger DID result in the expected direction (a decrease of 0.42 kg/m2; P = .33).
Effects on Percentages of Overweight or Obese Employees The unadjusted model showed that, within groups, the percentage of overweight or obese employees decreased over time at intervention worksites (by 4.5%; P = .02) and increased at control worksites (by 3.3%; P = .23). The DID between-arms results favored the intervention worksites (a decrease of 7.8%;, P = .02). In the adjusted model, within-worksite changes in the percentage of overweight or obese employees were of a different magnitude but remained in the same direction (decreases of 3.7%; P = .07, and increases of 4.9%; P = .1, at the intervention and control worksites, respectively), resulting in a net difference of 8.6% favoring the intervention in the DID analysis (P = .02).
Body Mass Index Distribution by Time and Condition At the intervention worksites, the curve of the adjusted BMI distribution shifted to the left between the baseline and postintervention points and was narrower to the expense of the right tail of the distribution (Figure 2). The area under the curve for BMIs below 24.9 (corresponding to healthy weight categories) was larger at postintervention. At the control worksites, the baseline and postintervention curves practically overlapped.
DISCUSSION The Images of a Healthy Worksite study was a worksite-randomized trial that tested environmental interventions targeting prevention of weight gain. A distinctive feature of this study was the participation of EABs that included company employees. Our results suggest that, after 2 intervention years, there was a favorable trend toward a larger decline in
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TABLE 1—Characteristics of the Cross-Sectional Samples (Baseline and Postintervention), by Study Arm: Images of a Healthy Worksite Study, 2005–2010 Baseline
Postintervention
Intervention Group (n = 1547), Mean 6SD or No. (%)
Control Group (n = 1067), Mean 6SD or No. (%)
P
Age, y
47.7 67.47
47.4 67.84
BMI, kg/m2
28.6 65.50
28.6 65.55
7.2 62.67
Psychological job demand scoreb BMI categoryc
Characteristic
Job insecurity scorea
Intervention Group (n = 839), Mean 6SD or No. (%)
Control Group (n = 345), Mean 6SD or No. (%)
P
.51
49 67.82
49.7 68.17
.18
.85
28.2 65.50
28.7 65.57
.75
7.3 63.32
.01
7.4 63.75
7.1 66.09
.02
31.9 68.72
32.5 610.81
.6
31.5 612.16
31.2 619.89
.78
.3
.03
1544 (100)
1068 (100)
837 (100)
344 (100)
Healthy weight
392 (25.4)
297 (27.8)
246 (29.4)
76 (22.0)
Overweight
631 (40.8)
407 (38.1)
354 (42.1)
153 (44.4)
Obese
521 (33.7)
364 (34.1)
237 (28.3)
115 (33.6)
1403 (100)
887 (100)
718 (100)
273 (100)
Secondary or less
241 (17.2)
201 (22.7)
131 (18.3)
74 (27.1)
College or less
882 (62.9)
561 (63.4)
454 (63.2)
165 (60.4)
Graduate level
280 (20.0)
124 (14.0)
133 (18.5)
34 (12.5)
1251 (100)
766 (100)
607 (100)
223 (100)
335 (26.8)
237 (30.9)
169 (27.8)
77 (34.2)
438 (72.2)
146 (65.5)
Educationc
Income, $c < 60 000 ‡ 60 000
916 (73.2)
529 (69.1)
1401 (100)
883 (100)
1285 (91.7)
African American Other
Racec
< .001
.04
.06
725 (100)
273 (100)
790 (89.5)
655 (90.3)
239 (87.6)
63 (4.5)
42 (4.8)
33 (4.6)
26 (9.5)
53 (3.8)
51 (5.8)
37 (5.1)
8 (2.9)
Genderc
1547 (100)
1068 (100)
838 (100)
345 (100)
Male
1054 (68.1)
594 (55.6)
493 (58.8)
216 (62.6)
493 (31.9)
474(44.4)
345 (41.2)
129 (37.4)
Importance of changing diet habits in the next 30 days (positive response)c
818 (58.5)
601 (66.3)
.001
401 (55.2)
163 (58.4)
.36
Confidence in changing diet habits in the next 30 days (positive response)c
981 (70.6)
675 (75.2)
.02
517 (72.2)
207 (76.7)
.16
Importance of changing PA habits in the next 30 days (positive response)c
832 (61.4)
623 (70.5)
< .001
412 (59.5)
180 (68.4)
.01
Confidence in changing PA habits in the next 30 days (positive response)c
996 (72.3)
670 (75.5)
.09
500 (71.4)
210 (78.4)
.03
1402 (100)
907 (100)
< .001
725 (100)
280 (100)
.01
Precontemplation
107 (7.6)
49 (5.4)
47 (6.5)
15 (5.4)
Contemplation
335 (23.9)
230 (25.4)
134 (18.5)
36 (12.9)
Action
111 (7.9)
112 (12.4)
56 (7.7)
38 (13.6)
Maintenance
849 (60.6)
516 (56.9)
488 (67.3)
191 (68.2)
1400 (100)
907 (100)
725 (100)
280 (100)
50 (3.6)
22 (2.4)
23 (3.2)
8 (2.9)
145 (10.4)
120 (13.3)
62 (8.6)
33 (11.8)
75 (5.4)
58 (6.4)
34 (4.7)
15 (5.4)
1130 (80.7)
707 (77.0)
606 (83.6)
224 (80.0)
Stage of change: PAc
1402 (100)
906 (100)
726 (100)
278 (100)
Precontemplation
95 (6.8)
51 (5.6)
45 (6.2)
21 (7.6)
Contemplation
472 (33.7)
370 (40.8)
210 (28.9)
91 (32.7)
Action
200 (14.3)
120 (13.3)
109 (15.0)
46 (16.6)
Maintenance
635 (45.3)
365 (40.3)
362 (49.9)
120 (43.2)
White
Female
Stage of change: fruit consumptionc
Stage of change: vegetable consumptionc Precontemplation Contemplation Action Maintenance
.08
.002
