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Discussion
Because it has been confirmed that African Americans have an increased burden of chronic disease risk that is exacerbated by unhealthy diets and limited physical activity, interventions for diet and physical activity behavior modification may alleviate this burden. Several studies published since 2000 were available for review, and based on the current literature, diet and physical activity interventions targeting African Americans need to be refined. This review evaluated the most current literature on diet and physical activity interventions among African Americans, and we emphasize that clinical progress was a major consideration in our review. The evidence shows that nutrition and physical activity lifestyle modifications alone can significantly improve predictors of various clinical outcomes in African Americans, but more research is needed to substantiate the clinical significance of the outcomes.
In a more recent, similar review, Pezmeki and Jennings examined physical activity outcomes without evaluating the effect of the behavior change on various health outcomes. Seven interventions included in our analysis overlapped with the previous review. Because the review by Pezmeki and Jennings aimed to examine physical activity outcomes exclusively, we saw a need to fill a gap in the literature by presenting a comprehensive examination of studies that promoted diet and physical activity behavior change to improve health outcomes, including major clinical indicators.
Although all 19 of the studies we reviewed demonstrated significance in various clinical outcomes, the most frequently reported variables were weight, BMI, SBP, and DBP. It was apparent that the African American participants in populations targeted by selected interventions were obese and prehypertensive. Mean decreases in SBP and DBP were sufficient to decrease blood pressure but not the number of people diagnosed with prehypertension. Although BMI remained in the obese range for participants in all 19 studies, mean weight loss reported amounted to approximately 3.0% of initial body-weight. Unfortunately, we did not find enough evidence to comment on the effect of diet and physical activity interventions on other clinical outcomes, including lipid and blood glucose levels.
Our findings are consistent with published research results that support using community-based settings for implementing interventions to improve diet and physical activity among African Americans. Our findings also indicate that churches may be useful in reaching communities beyond their congregations for study participation; several studies successfully recruited and reported changes among participants who did not attend church at the study's location. In addition, we found that some of the highest participant retention rates were among programs conducted in churches.
Eleven studies did not report using behavior theory in their intervention design, and this omission may indicate a weakness in the analyzed results of those studies. Unfortunately, compared with a past review of physical activity interventions among African Americans little progress has been made in increasing the number of studies that use health behavior theory in intervention program design. Research designed with a theoretical foundation better predicts and validates whether lifestyle interventions will promote changes in health behaviors while also providing a means to evaluate change processes in health behavior. Only about one-third of health-behavior–change studies conducted from 2000 through 2005 and reviewed by Painter et al reported using behavior theory in intervention design. Our results indicate a slightly higher proportion; 42.0% of studies used behavior theory models. Furthermore, of the 8 studies that used a behavior theory, 7 reported significant results, whereas the remainder of studies all reported significant results. It is possible that studies examined may lack explicit reporting of the use of behavior theories. We suggest that common health behavior theories be incorporated into intervention design, applied more thoroughly in research beyond mere consideration of their definition, tested in African Americans, and modified as necessary to better suit the population.
This review found no differences in select clinical outcomes (eg, weight, SBP, and DBP) between programs that offered physical activity education and those that offered physical activity plus diet education, although few physical activity-education only interventions were available for comparison. One study included in this review was noteworthy in that it found no differences in body composition (weight, waist circumference, and BMI) at a 6-month interval between participants who received a diet education intervention and those who received a diet plus physical activity intervention. This lack of difference suggests that both diet and physical activity should be considered major components of a lifestyle behavior change intervention until further evidence is available and examined. Other comparison issues noted were the lack of homogeneity among the education tools used in interventions and our inability to determine which specific education tools were used. Without this information, it is hard to generalize, repeat, and retest successful education programs as the NIH DPP has done.
Compared with programs aimed at improving physical activity and diet in predominately white populations, mean attendance and retention rates at programs for African Americans were lower. The mean attendance rate for studies with predominantly white participants was 95.0% compared with 58.0% for studies in our review with predominantly African American participants. In addition, studies with mostly white participants reported a mean retention rate of 87.0% compared with a mean of 80.0% reported for studies with mostly African American participants. Several studies identified effective retention practices for African American research participants, but because culture plays a central role in behavior choices, generic health messages may conflict with the cultural beliefs of minority populations. The increasing prevalence of coronary vascular disease among African Americans illustrates the need for culturally relevant associations between food and health, including the use of culturally tailored intervention components, such as lifestyle-change education to lower coronary vascular disease risk by modifying, not eliminating, cultural foods to improve diet and by suggesting culturally acceptable and attractive modes of physical activity. It is still necessary to improve both African American attendance and retention rates for health interventions. However, more than half of the studies in the current investigation (n = 10) did not report an attendance rate, thereby making attendance unavailable for evaluation. Not reporting attendance is notable because program attendance is imperative for participants to acquire the knowledge and skills needed to modify health behaviors.
Our study had limitations. Our review was only as good as the available studies analyzed. Not all included studies used randomization for participant allocation, and some of the results may show allocation bias. Another limitation is publication bias. Many relevant studies that were unpublished because of nonsignificant results would have been included in this review if published. Other analyzed studies did not use control groups for comparison, which may have introduced some experimenter bias for the overall conclusions.
This review provides researchers with current information on intervention program effectiveness and provides policy makers and health care practitioners with evidence about whether nutrition education and physical activity promotion interventions are valuable methods for improving the health of African Americans. The authors identified from the reviewed literature a common protocol for implementation of lifestyle interventions to prevent chronic disease in African American adults (Appendix). To our knowledge, there is no previously published analysis that encompasses all variables considered in this systematic review.
Nutrition and physical activity interventions promote positive changes in the health behaviors of adult African Americans by providing them with knowledge and resources about disease prevention. The reviewed studies have shown that these health interventions had a positive effect on the participants' dietary choices and physical activity habits, which translated to clinically relevant outcomes in communities, churches, and health clinics. Using health education and interventions designed to teach African American adults about healthy choices (eg, proper nutrition and adequate exercise) empowers them to make necessary lifestyle changes. Thus, potential exists for reducing preventable risks for diseases and comorbidities while positively affecting the health of the community. Future interventions should incorporate theoretical models appropriate for health-related issues and randomized controlled trial design into the basis of their programming, because this gives credence to evidence-based research.
The current literature suggests that more research is needed to determine the cost and sustainability of lifestyle intervention programs. We noticed in our review that the costs of designing and implementing interventions were rarely published, offering no guidance as to what the typical costs are of interventions. Additionally, a cost-benefit analysis would facilitate the awareness and spread of information about public policy and funding allocation. Sustainability of improved diet and physical activity behavior is also rarely noted. Programs are implemented and results are documented, but whether targeted populations are able to further or maintain progress after the cessation of the intervention is still in question.
Further research is required to substantiate the link between the intervention-induced diet and physical activity changes and related disease-risk biochemical markers. Such data could be documented on a clinical level, and the information on population disease-risk characteristics could become available. This type of data also adds to the potency of the argument for funding public education programs. Although many interventions have proven successful for African American populations, filling the information gaps will promote and substantiate further progress of intervention research and a subsequent improvement in overall health of African Americans and a reduction in population health disparities.
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