The growing incidence of chronic diseases has, in part, contributed to increased political and societal pressures to ensure public funds are allocated to the provision of services with known effectiveness. In other words, there is a call to action to ensure the programs and services implemented across Canada in population and public health are effective, and that they will result in improved health outcomes for Canadians. There is some evidence to suggest that current practices related to the promotion of healthy dietary behaviours may not adequately address inequities in health, and may even increase disparities. The purpose of this paper is to identify and summarize research findings on the effectiveness of population based interventions on community-based diet and nutrition, which was identified as a priority topic area in the annual report of the Ontario Chief Medical Officer of Health to the legislative assembly.
The health-evidence.ca registry was searched for reviews on diet and nutrition in May 2011. A standardized quality assessment tool was used to assess the methodological quality of each identified review by two independent reviewers. All search results were limited to reviews rated as being of strong methodological quality. Extracted data included age of participants studied in the review, research design, methodological quality rating, details of the interventions evaluated, details describing which outcomes where evaluated as well as how they were measured, and outcome data.
The diet and nutrition search identified 33 high quality reviews, 17 of which reported on outcomes of interest to this review. Outcomes evaluated included: improving diet (N=10), weight change (N=5), and body mass index (BMI) (N=5). Participants studied ranged from healthy adults to obese adults and adults diagnosed with pre-diabetes, as well as children, adolescents, and ethnic and low income populations. The interventions evaluated varied significantly across the reviews but can be classified as follows: improving diet, weight management, fruit and vegetable consumption, nutrition education, sodium reduction, cognitive/behavioural change strategies, lifestyle interventions, self-help interventions, and incentives.
Exposure to cognitive/behavioural change strategies results in statistically significant large effects on eating behaviours among adults. The evidence supports the provision of behavioural change interventions, particularly self monitoring plus one other self regulating intervention such as intention formation, feedback on performance, goal setting and review of behavioural goals, to improve healthy eating. While behavioural and education-based nutrition strategies are associated with healthier diets, there is some evidence to suggest that nutrition interventions may be associated with increased health disparities. For example, children from higher income families experience greater improvements in diet (e.g. healthier eating) compared to children from lower income families following exposure to a healthy eating intervention, and that White children consume fewer grams of fat per day compared to Black children. In addition, ethnic minority individuals were reported more likely to drop out of studies than White participants.
The evidence also illustrates that community based interventions significantly increase fruit and vegetable consumption among preschoolers and school-aged children, and among adults when the intervention is implemented in a workplace setting. However, the magnitude of effect may be insufficient to result in clinically significant health benefits. The most effective community-based interventions provided clear messages about increasing fruit and vegetable consumption; incorporated behavioural theories and goals, provided a consistent framework for implementation and evaluation; provided longer, more intensive interventions rather than one or two contacts; actively involved influential people such as family members; and targeted those whose knowledge and/or fruit and vegetable intake was low. Tailored nutrition education in comparison to general nutrition education appears to be a particularly promising practice among populations with low SES and different ethnicities, but not amongst adults in the general population. Finally, much of the evidence suggests that community-based diet and nutrition interventions are not associated with a positive impact on body mass index among children, adolescents, or adults although there is some evidence to suggest these interventions may be effective among those diagnosed with pre-diabetes.
Overall the evidence suggests that interventions targeted at weight loss are effective, particularly among those who are obese or have established high risk factors (pre-diabetes). However, significant effects, while still present in the medium term, (i.e. 2-3 years post intervention), are not maintained in the long term (5 years). Incentives were effective in reducing weight, although impact in the long term is not known. The impact of incentives on subgroup populations such as those with low socioeconomic status or different ethnicities has not been studied to date.
This review of the literature represents many systematic reviews and meta-analyses, primary studies and thousands of people. To some extent, the results illustrate that many population health and public health programs are associated with benefits to various populations, particularly related to outcomes such as healthy eating. However, there remains cause for concern given some of the evidence suggests that various interventions may in fact widen health disparities. As a result, higher SES and white populations benefit more from certain interventions than those from low SES and non-white populations. Much more research is needed to fully explore if and how interventions impact heath outcomes in different sub populations. However, the evidence presented here provides some direction for moving forward with practice, draws attention to some areas that require ongoing evaluation, and identifies some practices that may not be producing the expected impact and therefore should be examined critically in terms of future investment. While a great deal has been accomplished in population and public health programs there is still much work to be done!