This study reports on key outcomes for the MYP, which is the first community-based intervention to target reductions in unhealthy weight gain among Tongan adolescents, a population group undergoing rapid age-related increases in obesity prevalence. The MYP targeted selected behaviours in village and school settings and aimed to build the capacity of communities and schools to promote healthy eating, physical activity and healthy weight in adolescents. While there was a 1.5% relative reduction in body fat percentage in the intervention group, there was no difference between the intervention and comparison groups for the other anthropometric outcomes. Furthermore, the intervention group showed no consistent patterns of improved dietary and physical activity patterns and indeed showed a relative reduction in quality of life.
Changes in body composition and behaviours
The improvements in body fat percentage in the absence of improved outcomes in BMI and BMI-z is difficult to interpret. These findings could be explained by sufficient increases in physical activity to ensure that weight gain comes mainly from increases in lean mass rather than fat mass (32). While the MYP intervention activities did have a strong focus on increasing physical activity, the relevant behavioural indicator variables we measured (self-reported activity during school, after school and on the weekends, transport to and from school and screen-based behaviours) did not show any suggestion of increased physical activity in the intervention group relative to the comparison group. Differences in pubertal development between the groups may have been another explanation for the observed outcomes but this was not directly measured. However, body fat percentage was calculated using gender-specific equations that included age, height and weight for male adolescents and height and weight for female adolescents (28). Additionally, analyses were adjusted for age, gender and duration to control for differences in pubertal developments.
Also, we did not observe any clear pattern of improved eating patterns over the intervention period. While it was not known what types of food and drink students brought from home for lunch, it is likely that lunches brought from home would have been more healthy than the energy-dense, nutrient-poor food and drink that could be purchased at school (33), especially the commonly available deep-fried pancakes, noodles and sweetened drinks. Likewise, intervention students reported decreases in the purchase of snack foods on the way home from after school, but overall this was offset by increased consumption of soft drinks, biscuits/chips/snacks, takeaway foods, and chocolates and sweets at home. Taken together, these results indicate that while fewer students purchased unhealthy food on the way home from school, more of these items were available at home. Further examination of the purchasing patterns of Tongan adolescents is needed, given the high consumption of soft drinks and the very high prevalence of obesity.
There are a number of factors that may have contributed to the minimal findings with regard to the anthropometric and behavioural changes. First, whole-of-community intervention programmes have long establishment phases and the real momentum in the MYP programme was occurring at the end of the intervention period (19). Undertaking measurements at the start and end of the intervention period truncated the total duration of intervention time – three school years is shorter than three calendar years because of the school holidays when adolescents are harder to access. Second, the intensity of the dose delivered by the MYP may have been insufficient to effect beneficial anthropometric and behavioural changes. Certainly, the intervention dose was reduced when intervention activities were severely disrupted during two significant national events: the 80-day mourning period following the death of the King in September 2006 and a subsequent period of major civil unrest that erupted 2 months after the death of the King. Some intervention activities were not implemented at all as a result of the mourning period. Third, policy-based interventions during the MYP were limited, and while some efforts were made to implement school food policies, the enforcement of these was minimal. The fourth, and probably most important reason for the lack of beneficial anthropometric and behavioural outcomes, relates to socio-cultural factors. Tonga is a society with very strong socio-cultural influences that underpin food-related behaviours (34), physical activities and body size perceptions (35). These socio-cultural factors include the strong values of love, nurturing and respect that underpin food selection, distribution, volumes and consumption (10,12), the high status afforded certain obesogenic foods like confectionery in contemporary Tonga (3,13) and the low status of fruit and vegetables, which are not seen as an essential component of a meal (12). In terms of physical activity, there are strong expectations that adolescent girls in Tonga should be engaged in home-based activities (chores and homework) after school and recreational physical activity is discouraged (36). The relative energy expended in chores is likely to be significantly less than in recreational physical activities and sports (37). A greater integration of strategies to address these and other socio-cultural factors into the intervention may have strengthened the ‘dose’ of the overall intervention and led to more beneficial outcomes. While preliminary socio-cultural interviews informed the intervention, the short lead-in time prior to intervention activities limited the full extent to which socio-cultural factors could be conducted and integrated into the intervention (38). It must also be highlighted that the lower levels of weight gain observed in male adolescents compared to the female adolescents during the project indicates the importance that gender plays in values, behaviours and lifestyle. The role of gender was perhaps insufficiently considered in the development of the intervention programmes, and future interventions and research must include greater consideration of the impacts of gender on adolescents.
In hierarchical societies with a collective ethos, such as Tonga, interventions that target social groupings, e.g. families, schools and churches, may be more effective than those that rely on individual behaviour changes. Furthermore, a multi-pronged approach that engages government leaders to implement policies, community leaders to role model and influence practices, and families to influence adolescents' behaviours may be more effective in societies that are hierarchically organized than only targeting a specific age group, e.g. adolescence, that has relatively little status or autonomy. It seems that the community capacity-building approach taken in MYP was probably necessary but not sufficient for slowing the rapid weight gain in this population. Other innovative strategies will need to be tested to address the powerful socio-cultural barriers to healthy weight in the Tongan community.
One of the measures of quality of life showed a smaller increase in the adolescents from Tongatapu (intervention group) compared to the less urbanized, outer island of Vava'u (comparison group). The interpretation of this finding is uncertain and a potential explanation may be that adolescents on the main island are exposed to more pressure in terms of achieving high examination results and obtaining employment or overseas tertiary education places. Further analyses or studies will be needed to explore this issue.
The strengths of MYP were that it was the first major, solutions-based approach to an enormous health problem in Tonga and that it used a whole of community approach targeting the critical period of adolescence. Solid conclusions which advance knowledge can usually be made from such solutions-oriented research (39)– in this case, that the intervention did not have sufficient duration, intensity or integration of socio-cultural factors to bring about the desired changes in reducing overweight and obesity among Tongan adolescents. The major caveat to the strength of this conclusion is that the quasi-experimental approach of having three districts on a more urbanized island for the intervention populations and a more rural island for the comparison population intrinsically runs the risks of false positive conclusion (type 1 error) or false negative conclusion (type 2 error). In this instance, we have made a negative conclusion about the impact of MYP so a type 2 error is possible. For example, the trajectory of weight gain of adolescents on Vava'u may naturally be lower because they lead a more traditional lifestyle compared to those on Tongatapu who watched significantly more television and consumed more canned corned mutton and soft drinks than adolescents on Vava'u and Ha'apai (3,13).Therefore, it is possible that MYP was successful in reducing unhealthy weight gain by moving the trajectory of weight gain in the adolescents on Tongatapu down to the same trajectory as the Vava'u adolescents, thus showing up as no difference in trajectories. However, there is no evidence from the behavioural data that the adolescents on Tongatapu made significant progress towards healthier behaviours and the null result remains the most likely true conclusion. Other designs, such as cluster randomized trials, were considered for MYP but rejected because of other design considerations such as achieving sufficient clusters and the high risk of the interventions contaminating the comparison populations in a small island nation like Tonga. Cluster effects associated with the practicalities of data collection, such as differences in seasonality of measurements (e.g. clashing with school ‘seasons’ for examinations or inter-school sports) or measuring each arm of the study in blocks, can potentially add bias to the measurements of both behaviours and quality of life. In addition, the lower numbers of completed behavioural questionnaires completed at follow-up may have introduced some bias to those results, and are difficult to interpret.
One of the major lessons learned during the MYP project was around the nature of the interventions needed for populations where socio-cultural factors are strong determinants of eating, physical activity and body size perceptions. Qualitative studies on these socio-cultural factors were conducted in Tonga prior to the start of the intervention and these informed the development of the MYP action plan as well as the intervention. Subsequent quantitative and qualitative studies were conducted which helped to inform the interventions. However, the extremely strong impact of socio-cultural factors on behaviours and body size in this population and the inevitable delays in collection and analysis and feedback of the socio-cultural data were underestimated.
The school food policy was the only policy to be implemented in intervention schools between 2006 and 2008 but this policy was neither audited nor enforced. The implementation of more policies relating to food and physical activity environments would have provided high-level support for the MYP intervention. For example, the National Non-Communicable Diseases Committee has highlighted the need for a compulsory physical education policy for schools (40). Policies to encourage students to be physically active at school, either at lunch time or during physical education periods, would have supported the MYP action plan. National-level policies and regulations that promote physical activity would increase opportunities to be active outside school hours, e.g. more control of dogs and more footpaths. More emphasis on the wider food environment is also needed, through the use of policy to influence pricing and accessibility of healthy foods (13).