Introduction

Obesity increases risk for a number of diseases, including hypertension, type 2 diabetes, dyslipidemia, coronary artery disease, osteoarthritis, and postmenopausal breast cancer (1). The prevalence of obesity has increased significantly over the past 30 years, and ~32% of adults in the United States are now obese (2). The prevalence of obesity is particularly high among black women (54%), and close to 15% of black women are considered extremely obese (Class III obesity) (2). Morbidity and mortality from many obesity-related diseases are also higher among black women than among white women. For example, data from the National Health and Nutrition Examination Survey (NHANES) 1999–2002 showed that the age-adjusted prevalence of diagnosed diabetes was much higher in black women than in white women (12.2% vs. 4.5%) (3). Non-Hispanic black women also had higher age-adjusted mortality rates for cardiovascular disease (322.5 vs. 231.7 per 100,000) and colorectal cancer (21.6 vs. 14.5 per 100,000) than non-Hispanic white women in 2005 (ref. 4).

Efforts to develop and evaluate weight loss programs for black women are needed (5). A number of large randomized trials have examined weight loss among white women. Overall, there are fewer interventions that have focused specifically on black women, even though data suggest that ~68% of obese black women are trying to lose weight (6). Nonetheless, in a recent trial that compared the Zone, Atkins, Ornish, and LEARN diets, only 6% of participants were black (7). Even in studies where black women are well-represented, the results are often less than encouraging (8,9). For example, in the Diabetes Prevention Program, approximately half as many black participants as white participants achieved the 7% weight loss goal at 6 months (10).

A number of qualitative studies have provided some insight into weight loss among black women and underscore the need for culturally proficient weight loss interventions (11,12). These studies emphasized the importance of addressing social support, honoring the importance of traditional foods, especially in terms of taste and texture, respecting the significant psychological and physical challenges to incorporating daily physical activity, and offering strategies for weight loss maintenance and behavioral changes that lead to weight loss (11,12).

With the importance of culture in mind, we developed a culturally proficient weight loss and maintenance intervention for black women. The Obesity Reduction Black Intervention Trial (ORBIT) was designed to test the efficacy of this approach. This article presents the results of the 6-month weight loss program for 213 black women aged between 30 and 65 years.

Methods and Procedures

Study design

Full Institutional Review Board approval was obtained from the University of Illinois at Chicago (UIC), where the trial is being conducted. ORBIT is a randomized controlled trial of a culturally adapted 6-month weight loss intervention followed by a 1-year weight loss maintenance intervention. The study was conducted in two cohorts. Recruitment for cohort 1 began in May 2005 and ended in August 2005. Recruitment for cohort 2 began in July 2006 and ended in September 2006. Recruitment strategies included a mass e-mail that was sent to all UIC faculty, staff, and students (~36,000 recipients) and face-to-face recruitment at local grocery stores, churches, and nearby health care centers. Women who were interested in the program were asked to complete a short eligibility interview. Eligibility criteria included: female, self-identified as African American or black, aged between 30 and 65, BMI between 30 and 50 kg/m², able to participate in a program requiring 30 min of uninterrupted walking or other moderate activity, able to attend class at scheduled times, and return of a medical approval form signed by a physician. Exclusion criteria included: planning to move from the area during the intervention, pregnant, nursing, planning a pregnancy over the course of the 18-month intervention, use of illegal drugs, intake of >2 alcoholic drinks per day on a daily basis, treatment for cancer in the past 5 years (excluding skin cancer other than melanoma), inability to exercise due to emphysema, chronic bronchitis, or asthma, use of medically prescribed weight loss medication, participation in a formal weight loss program, and use of a cane, walker, or wheelchair to enhance mobility (cohort 2 only). Eligible women who gave informed consent and completed a baseline interview were randomized to either the intervention group or the control group. Data were collected at baseline and at the end of the 6-month weight loss intervention.

Measures

All data collection personnel were trained and certified in interviewing and anthropometric measurements. All questionnaires were interviewer-administered.

Demographics and anthropometrics. The sociodemographic questionnaire inquired about date of birth, education, income, occupation, employment status, and marital status. Height was measured to the nearest 0.1 cm using a Seca 214 portable stadiometer (Seca, Hanover, MD), and weight was measured to the nearest 0.1 kg using a Tanita BWB-800 digital scale (Tanita Corporation of America, Arlington Heights, IL). Participants removed their shoes and any heavy outer clothing for the anthropometric measurements. BMI was then computed from height and weight.

Dietary intake. Dietary intake was measured using the Block '98 Food Frequency Questionnaire (FFQ) (13). The Block FFQ asks about frequency of consumption in the past year and usual portion size for 110 different food items. The food list was developed using food intake data from the NHANES III. Separate lists were developed using data from blacks, non-Hispanic whites, and Hispanics, to ensure that the final food list would include foods that are frequently consumed among these population groups. Validity for the Block FFQ was established in a number of studies, including comparisons to plasma and multiple days of diet recalls (14,15). The Eating at America's Table study used four 24-h recalls collected over the course of a year as a reference measure to estimate the correlation between true nutrient intake and intake measured by the 1995 Block FFQ (16). For women, the deattenuated correlations from the measurement error model were 0.45 for energy, 0.66 for fat (% kcal), and 0.80 for fiber adjusted for energy intake (16). Data from the Block '98 were used to calculate nutrient intake, food group intake, and other dietary variables, including the Healthy Eating Index (HEI) (17). The HEI is a measure of overall diet quality developed by the US Department of Agriculture's (USDA) Center for Nutrition Policy and Promotion. Components of the index include servings of the five food groups in the USDA's Food Guide Pyramid (18), total fat and saturated fat as a percentage of energy, sodium, cholesterol, and variety. Scores range from 0 to 100, with a higher score reflecting a healthier diet.

Physical activity. Physical activity was measured using the International Physical Activity Questionnaire-Long Format (IPAQ) (19). The long IPAQ is designed to assess self-reported physical activity during the past 7 days. Items assess physical activity across a diverse set of domains, including leisure time physical activity, domestic and yard physical activity, work-related physical activity, and transport-related physical activity. Participants are asked to only report activity that they engaged in for at least 10 min at a time. The psychometric properties of the IPAQ compare favorably to other commonly used self-reported physical activity measures. Specifically, test–retest reliability was good (Spearman's r = 0.79), though criterion validity was only fair to moderate (Spearman's r = 0.33, 95% confidence interval 0.26–0.39, for the comparison between long-form IPAQ data and accelerometer data) (19).

Weight Loss Intervention

The development and delivery of the intervention were based on Social Cognitive Theory (20) and thus focused on changes in cognitions, behaviors, and social support related to weight loss. According to Social Cognitive Theory, modeling or observational learning is a powerful contributor to behavioral change (20). Individuals are more likely to model behavior that has a positive outcome, as well as the behavior of someone similar to themselves. The intervention provided ample opportunity for observational learning to occur, both via the interventionists and fellow participants. The intervention also presented multiple avenues to enhance self-efficacy, with repeated rehearsal of stimulus control, problem solving and other weight loss strategies, as well as the opportunity for monthly motivational interviewing (MI) sessions.

In addition to Social Cognitive Theory, the intervention incorporated tenets related to the practice of culturally competent research (21). Culturally sensitive interventions require the recognition of the beliefs and practices of the particular social, ethnic, and age group for whom the intervention is being developed, appreciation of the roles these factors play in participants' lives, and considerate incorporation into the intervention (21). To create a culturally sensitive intervention we incorporated information gained from focus groups (22), a pilot intervention (23), and related scientific literature (5). We focused on food, family, music, social roles and relationships, and spirituality/religion. For example, in discussing dietary changes, acknowledgment was given to the importance of food in the African-American culture and ways to integrate this value with healthful eating. We also offered specific information on alternatives to traditional foods that reduced caloric and fat content but did not sacrifice flavor. Several sessions included discussions of how family and social relationships could serve as both sources of support and barriers to lifestyle changes. Participants strategized about how to address family resistance, create healthy menus that all family members would enjoy, and maintain healthful behaviors in the face of social pressure and events. Importantly, the intervention groups themselves became a valuable source of support for their members, and seeing each other was a major incentive for attending classes. Although music may seem like a minor component, participants recognized music as a facilitator for physical activity, and the intervention supported this in its use of high tempo, high energy music that the participants enjoyed. The physical activity intervention also addressed barriers to physical activity such as hair care, safety, weather, access, and time. The intervention respected the importance of religion and worship in many participants' lives and recognized the ways in which their faith influenced their perspectives on health. Finally, the intervention incorporated body image and reasons for weight loss (24,25).

The weight loss intervention was conducted in a small group format and met twice weekly on the university campus. Participants were also offered monthly MI sessions. All participants were encouraged to adopt a low-fat, high-fiber diet with increased fruit and vegetable consumption and to increase their physical activity. Dietary objectives included reducing dietary fat to <30% of total daily calories, increasing dietary fiber to a minimum of 25 g per day, and increasing fruit and vegetable consumption to a minimum of five servings per day. Most women entered the program at very low levels of fitness. Exercise objectives included exercising at a moderate-to-vigorous level a minimum of 3–4 times per week for at least 30 min. One meeting each week was 90 min long. This meeting included a 30–40 min didactic session in which the group leaders led discussions related to diet, physical activity, and weight loss. These discussions often included hands-on activities such as weighing and measuring foods according to one's typical portions and then according to recommended portions, a field trip to the grocery store to practice reading food labels and to compare and contrast various food choices, creating weekly meal plans, and preparing a healthier version of a particular dish. The didactic session was followed by a physical activity session that incorporated aerobic activity as well as strength and flexibility training. To increase variety, some physical activity sessions included salsa dancing, African dancing, belly dancing, yoga, and Pilates. The second meeting of each week was 60 min in length and included a 30–40 min physical activity class and discussions of topics related to increasing regular physical activity.

In addition to group sessions, participants were encouraged to attend monthly individual MI sessions with a trained interventionist. These sessions were conducted face to face or over the phone, lasting ~20–30 min. Each MI session addressed either diet or physical activity. The goal of MI is to assist individuals to work through their ambivalence about behavior change within a supportive climate where they feel comfortable expressing both the positive and negative aspects of their current behavior.

Control intervention

Women in the control group received newsletters that covered general health and safety topics on a weekly basis throughout the 6-month period. In addition, a staff member who was not affiliated with the weight loss intervention telephoned control participants once a month. In this call, participants were offered the opportunity to ask questions or express concerns about the information contained in the weekly newsletter.

Statistical analysis

The primary aim of the study was to estimate the efficacy of a culturally proficient 6-month weight loss intervention followed by a 1-year maintenance intervention. The secondary aim was to assess changes in diet and physical activity at 6 months and 18 months after randomization. Data from the 6-month weight loss intervention are reported here; the maintenance intervention is still in progress.

SAS v. 9.1 (SAS Institute, Cary, NC) was used for all analyses. The Block '98 FFQs were sent to NutritionQuest (Berkeley, CA) for scoring. Participants with total energy <500 or >5,000 kcal/day were excluded from all analyses of dietary intake. This exclusion is relatively standard and has been used in a number of large dietary trials, including INTERMAP (26). The IPAQ was scored according to the November 2005 long-form scoring protocol (27). All physical activity variables were log-transformed before testing to improve normality, after adding 1 to all values to eliminate values of 0. The approximate geometric means of the physical activity variables for each group at baseline and 6 months were calculated by exponentiating the arithmetic means of the log-transformed values, then subtracting 1 from the result.

Differences in baseline characteristics between the intervention and control groups were tested for significance using the Wilcoxon rank sum test for income, t-tests for all other continuous variables, and ²-tests for employment and marital status. Tests for baseline differences were conducted for all randomized women, then repeated for the subset of women with data from the 6-month visit.

Spearman's correlation coefficients were used to test the associations between BMI change and class attendance or MI attendance among women in the intervention group. Analysis of covariance was used to test for differences between the intervention and control groups after the 6-month weight loss intervention, controlling for cohort and the baseline value. All physical activity variables were log-transformed as described above before they were entered in the analysis of covariance.

Differences in retention and attendance between cohorts within the intervention group were tested for significance using a ²-test for retention and t-tests for attendance. In addition, a subgroup analysis was performed to investigate whether the efficacy of the ORBIT intervention varied by baseline BMI. An interaction term for intervention group baseline BMI was included in the model, first with baseline BMI as a continuous variable, then with baseline BMI as a categorical variable (Class I (30 to <35 kg/m²), Class II (35 to <40 kg/m²), and Class III (40 kg/ m²) obesity). The Pearson correlation between BMI change and baseline BMI among intervention women was also calculated. Finally, one-way ANOVA was used to test for differences in mean BMI change between women in the intervention group who began the study in the Class I, Class II, and Class III obesity subgroups.

Results

Participants

A total of 213 women were randomized; 107 to the intervention group and 106 to the control group. At baseline, there were no statistically significant differences between women randomized to the intervention and control groups. However, among the subset of women with valid diet data at baseline and 6 months, the mean HEI score at baseline was higher in the control group than in the intervention group (Mean = 56.0 (s.d. = 10.6) vs. Mean = 52.3 (s.d. = 12.6), P = 0.03). Women in the control group who had physical activity data at 6 months also reported more moderate physical activity than intervention women (geometric mean = 85.0 min/day vs. 65.7 min/day, P = 0.03). Participant characteristics are presented in Table 1.

Table 1 - Participant characteristics at baseline, ORBIT.

Full table (27K)

Retention and attendance

One hundred (93.5%) women in the intervention group and 98 (92.5%) women in the control group completed both the baseline and the 6-month assessment. Participants in the intervention group attended a mean of 53% of the intervention classes (total = 47 for cohort 1 and 46 for cohort 2) and 53% of MI sessions (total = 6) (Table 2). There was a significant correlation between BMI change and overall class attendance (Spearman's r = 0.46, P < 0.001). However, the correlation between BMI change and MI attendance was significant for cohort 1 (Spearman's r = 0.41, P = 0.002), but not for cohort 2 (Spearman's r = 0.09, P = 0.54).

Table 2 - Retention, class attendance^a, and attendance at motivational interviewing (MI) sessions for women in the intervention group, 6-month weight loss intervention, ORBIT.

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BMI and weight

The average BMI at baseline was 39.2 (5.7) kg/m², and 44% of randomized participants had a BMI over 40 kg/m². As shown in Table 3, there was a significant difference between groups in both BMI and weight at 6 months, controlling for baseline value and cohort (P < 0.001). Women in the intervention group lost an average of 3.0 kg (s.d. = 4.9 kg), compared to a gain of 0.2 kg (s.d. = 3.7 kg) in the control group. In the intervention group, mean BMI decreased by 1.14 kg/m² (s.d. = 1.88 kg/m²), whereas the mean BMI increased by 0.10 kg/m² (s.d. = 1.37 kg/ m²) in the control group. Weight change was not uniform within groups. For example, in the intervention group, 26% of participants lost 5% of their initial body weight, 25% lost 2.5 to <5%, 29% lost 0 to <2.5% and 20% gained weight. By comparison, in the control group 61% gained weight and only 5% lost 5% of their body weight.

Table 3 - BMI and weight at baseline and after 6-month weight loss program, ORBIT.

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The efficacy of the ORBIT intervention did not appear to vary significantly by baseline BMI. When an interaction term for intervention group baseline BMI was included in the regression model, there was no significant interaction, whether baseline BMI was represented as a continuous variable (P = 0.72) or a categorical variable (Class I, Class II, Class III obesity, P = 0.50). Similarly, the correlation between baseline BMI and BMI change for women in the intervention group was not significant (r = –0.02, P = 0.83). For intervention women in obesity Class I at baseline, the mean (s.d.) BMI change was –1.21 (1.66) kg/m²; for women in obesity Class II, BMI change was –1.16 (1.39) kg/m², and for women in obesity Class III, it was –1.06 (2.35) kg/m². These means were not significantly different (P = 0.94).

Dietary intake

Table 4 shows the dietary intake data. Overall, the women consumed a high-calorie, high-fat, and low-fiber diet at baseline. At the postintervention visit, there was a significant difference between groups in fruit consumption, with women in the intervention group increasing their intake from 1.31 (s.d. = 1.02) servings/day to 1.86 (s.d. = 1.21) servings/day. There was also a significant difference between groups in the HEI score. The mean score of women in the intervention group increased from 52.3 (s.d. = 12.6) to 63.0 (s.d. = 12.3), moving the women from the lower to the middle range of the "needs improvement" category. There were no significant differences between the groups at the postintervention visit in total energy, dietary fat, dietary fiber, or vegetable consumption.

Table 4 - Diet at baseline and after 6-month weight loss program, ORBIT.

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Physical activity

Table 5 shows self-reported physical activity at baseline and postintervention. Women in the intervention group reported more vigorous activity (P < 0.001) and moderate-to-vigorous physical activity (P = 0.01) than women in the control group postintervention, controlling for baseline activity and cohort. Women in the intervention group reported walking more than women in the control group, but this difference was not statistically significant (P = 0.07). The difference in moderate activity at 6 months was statistically significant (P = 0.05).

Table 5 - Physical activity at baseline and after 6-month weight loss program, ORBIT.

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Discussion

This article documents the feasibility and efficacy of a 6-month culturally proficient weight loss intervention designed for black women. Over 25% of the women randomized to the intervention group lost 5% of their initial body weight over the course of the 6-month intervention, compared to only 5% of women in the control group. Mean weight loss for women in the intervention group was 3.0 kg, whereas women in the control group gained an average of 0.2 kg. Although this weight loss is relatively modest, it is consistent with the results reported for other weight loss programs conducted with black women (23,28,29,30). In addition, weight losses of 5% have been shown to alleviate the burden of many chronic diseases, including hypertension and diabetes (31,32). These results should be considered in the context of data showing an average weight gain of 0.5–1 kg per year in untreated, obese individuals (33). In this study, the control group gained on average 0.2 kg over the 6-month period.

Although members of the intervention group lost significantly more weight than members of the control group, weight change in the intervention group varied widely, from a 19.2 kg weight loss to 6.5 kg weight gain. This variability has important implications for the design of future weight loss interventions. In most behavioral weight loss programs, treatment is provided uniformly to all participants regardless of response (34). Future studies might explore the feasibility and efficacy of intensifying intervention efforts depending on participants' response to treatment.

Overall, women in the intervention group made significant changes in their dietary and physical activity patterns. Although there was no significant difference in energy intake between groups at 6 months, women in the intervention group did report consuming more fruit than women in the control group. A higher intake of fruits and vegetables has been associated with smaller increases in BMI (35). In addition, overall diet quality, as measured by the HEI, was higher for women in the intervention group than for women in the control group. Studies suggest that focusing on diet quality may be more important for producing weight loss than targeting a single nutrient (e.g., dietary fat) (36).

Women in the intervention group also exhibited improvements in their physical activity patterns, with increases noted for both moderate and vigorous activity. This is an important behavioral change given the benefits of physical activity for weight loss and maintenance of weight loss, including energy expenditure and its association with decreased energy intake and improved eating patterns (37,38,39). It is likely that at least some of the increase in physical activity was related to the women's participation in ORBIT's biweekly exercise classes. Although many women were able to successfully integrate regular physical activity into their lives outside of class, for others this remained a significant challenge. Many worked full time and/or served as caregivers to children, elderly parents or grandchildren, a common condition for many African-American women. As a result, time, energy, and motivation were the three primary barriers to engaging in physical activity. Despite discussions of ways to overcome these barriers, the most common solution was attending the ORBIT classes. This is of concern because the long-term benefits of exercise require ongoing participation in physical activity, and it is likely that many women stopped exercising once classes were no longer offered. Future interventions may need to concentrate on linking participants with physical activity resources that are regularly available in their communities.

The ORBIT 6-month results should be interpreted with the limitations of the study in mind. Self-report of diet and physical activity is not optimal. Under-reporting of food intake by obese individuals is a well-known problem when studying diet and obesity (40). Just as dietary intake is often under-reported, physical activity is often over-reported when assessed by self-report (41). Moreover, there is evidence to support the hypothesis that overweight and obese individuals have a greater tendency than normal-weight individuals to overestimate physical activity (42). Also, because the study was voluntary, asked for an 18-month commitment, and required that women obtain physician approval, we expect that participants were more highly motivated than average, potentially creating a biased sample. A further limitation is the use of BMI as the primary measure of obesity. The health risks associated with obesity may not be captured by this single measurement, and body fat distribution plays an important role in the risks associated with obesity (43,44). Finally, although control participants received regular contact from study staff, the trial did not strictly control for attention, leaving open the possibility that observed differences between groups were due to attention alone. However, a true attention placebo group would have required holding twice-weekly classes, which would have required a significant fraction of the resources available for the study and would almost certainly have been poorly attended (45). In an earlier study with an attention placebo group, attention alone did not result in significant behavior change (46). No-treatment control groups have been used effectively in a number of large randomized trials, including the Women's Health Initiative (47) and the Weight Loss Maintenance trials (48).

In conclusion, women in the ORBIT intervention group lost significantly more weight than women in the control group. However, mean weight loss after 6 months was fairly modest, and only 26% of women in the intervention group lost at least 5% of their initial weight. Clearly, further efforts are needed to enhance the effectiveness of weight loss programs among black women. Such efforts will need to recognize the sociocultural experiences of black women, and interventions will need to go beyond the individual and include the community and the built environment.

Disclosure

The authors declared no conflict of interest.

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Acknowledgments

The ORBIT study is supported by the National Cancer Institute (CA105051). We thank all of the women who gave of their time to participate in the study. We also thank our project coordinator and recruitment and intervention staff, whose efforts to effectively recruit participants, conduct the intervention, and retain the women in the study helped advance our knowledge of this population. Finally, we thank Jacqueline Restrepo, Beth Schneider, and Guadalupe Compean for their technical assistance.