In this cluster-randomised controlled trial, we evaluated a 10-weeks multi-component intervention to improve dietary quality of out-of-home food consumption conducted on an Asian university campus. The intervention increased the proportion of consumers having at least one healthier out-of-home dish per week. In particular, the intervention increased the consumption of dishes prepared with the healthier oil blend and dishes prepared with lower-sodium salt. In terms of dietary intakes from out-of-home dishes, the intervention decreased the intakes of monounsaturated and total fat.
The intervention mainly increased the consumption of healthier oil blend prepared dishes and lower-sodium salt prepared dishes. These two types of healthier dishes were incorporated by default during dish preparation by the food vendors. Decals stating the use of healthier oil were displayed at point-of-purchase. The intervention did not significantly change the consumption of the other two types of healthier dishes, the lower-calorie- and brown rice-dishes. Both lower-calorie dishes and brown rice were highlighted by decals at the point-of-purchase and stall directories, but were not the default option (except for two stalls which had 20% or less brown rice incorporated in all chicken rice dishes). This finding suggests that environmental dietary interventions are more likely to be successful when the healthier ingredients are used by default. This supports the theory that habitual human behaviour tends to be automatically cued by the environment without much conscious awareness or deliberation (43). This strong disposition to go with default options during decision making, can therefore be capitalized to promote healthier eating behaviours (44). Conventionally, a default is viewed as ‘the option provided to the consumer if they do not explicitly state their preference’ (45). In this study, with the default being oil used in food preparation, participants did not have alternatives (e.g. foods cooked with high saturated-fat oil) to choose from at the food centre. Our finding is consistent with the results of an experiment conducted in a Dutch university on the choice of bread and topping combinations by students and staff (46). A strong default effect was observed in the study when the majority of the participants chose to go with the default option (whole wheat, brown or white bread) and deemed it to be attractive, regardless of the type of topping offered.
Although the intervention resulted in a higher proportion of participants consuming dishes cooked with healthier oil blends (35–37% substitution of palm oil with soy bean oil), the saturated fat and poly-unsaturated fat intakes were comparable between arms, and the mono-unsaturated fat intake from out-of-home foods was reduced in the intervention arm. The decreased total fat intake in the intervention arm may partly explain the decreased mono-unsaturated fat intake. However, in sensitivity analyses (Supplementary Table 3), when fatty acid intakes were expressed as a percentage of energy from total fat, the mono-unsaturated fat intake reduction in the intervention arm was not statistically significant while increases in polyunsaturated fat intake in the intervention arm were. These changes in relative intake of fatty acids may be due to the fatty acid composition of the healthier oil relative to palm oil. Specifically, the healthier oil blend had lower mono-unsaturated fatty acid percent (6%), lower saturated fatty acid percent (10%) and higher poly-unsaturated fatty acid percent (20%) compared with the default palm oil used in control centers and during pre-intervention. The healthier oil blend was still relatively high in saturated fat. Ten intervention cooked food stalls (32%) were observed to have used additional one or more cooking oil/fat (e.g. margarine and/or butter). These findings highlight the need to consider increasing percentages of palm oil substitution with healthier oils and encouraging the use of healthier cooking fats and unblended oils like soy bean or canola oil.
We also observed a modest increase in dietary fibre consumption from out-of-home dishes in the intervention group after adjusting for pre-intervention dietary fibre and energy intakes. However, this exploratory finding may be due to chance. Further trials may be warranted to establish this finding.
Our finding that offering brown rice, and promoting brown-rice and lower-calorie dishes did not significantly increase their consumption is consistent with similar interventions in other countries. A worksite cafeterias trial conducted in the Netherlands which displayed a “Choices” logo, did not improve lunchtime food choices (47). The authors suggested that menu labelling might be more salient to consumers who are already in the preparation and action phase in the Transtheoretical Model of Behavior Change (48) with regard to healthier eating. Likewise, point-of-purchase prompts did not result in a significant change in choice of lower-salt instead of regular soup or lower-fat instead of regular croissants in a Dutch hospital (49). In Belgian university canteens, posting of nutrition information using a 3-star rating system with a descriptor of unhealthy nutrient contents also did not significantly improve meal choices or nutrient intakes (15). Contrary to these findings, when a traffic-light food labelling program was implemented at a worksite canteen in Taiwan the availability of healthier main dishes and the proportion of consumers utilising the traffic-light food label to select food increased significantly (28).
Unlike the use of healthier oils, dishes prepared with lower-sodium salt were not highlighted to consumers in the HDP. There is evidence to suggest that signalling changes in salt content to consumers can be counter-productive. Reduced-salt labels have been suggested to induce negative taste expectations of soups and compensatory actions such as adding more salt (50). As sodium content can be gradually reduced without consumers noticing a difference, and as people adapt to lower sodium content of dishes over time, using covert, rather than overt approaches to reduce sodium consumption has been suggested (50). When product reformulation was compared to an information provision campaign in the United Kingdom government’s salt reduction programme, the observed decline in dietary salt intake was largely attributed to product reformulation (51). Food labelling might be less effective due to its reliance on consumers’ attention, ability to interpret the labels and willingness to choose the healthier option (51).
Policies that restrict the availability of unhealthier food options are sometimes viewed as an infringement of personal choices (15). However, this is less likely to be a concern for changes such as the type of fat that may not considerably alter the sensory properties of food. Similar approaches such as restricting the use of trans-fat containing oils has successfully removed trans-fat from the food supply with little consumer objection (52). A more salient consideration for such interventions is the willingness of food vendors to use healthier oils. Apart from removing the price barrier by subsidising healthier oils, the implementation of this intervention was led by facilities management and received strong institutional support. This finding is aligned with other studies which show that institutional support is a key determinant of intervention success (53). Oil substitution in menu reformulation is more covert as compared to substituting white rice with brown rice (54) and offering brown rice as the default may pose other challenges. Nevertheless, taken together, findings from our study and previous studies suggest that menu reformulation should be prioritized before menu labelling to improve dietary quality of out-of-home dishes as it is less dependent on consumers’ utilization of information provided (55,56).
The strength of our study lies in evaluation of the program in a real-world setting using a rigorous cluster-randomized design study. The use of food diaries enabled the collection of detailed dietary information. Our study also had several limitations. While we planned for a systematic sampling approach to recruit participants, a convenience sampling was employed for feasibility reasons. Participants who were willing to participate may have been more interested in healthy eating as compared to those who did not participate. However, this is likely to be applicable to both the intervention and the control centers and hence may not affect internal validity. Our study results may be more generalizable to other IHLs and workplaces where there is likely to be greater institutional control over the implementation of the intervention. The higher than expected dropout rate (39%) in our study was also observed in other dietary worksite interventions (53). Post-intervention data were collected near exam period which may have contributed to participants not returning food diaries. In addition, similar to other dietary interventions, the study was conducted as an open trial due to the difficulty in blinding both researchers and participants to the changes introduced from the intervention. The 10-weeks intervention duration may have been insufficient to capture dietary habits such as replacing white rice with wholegrain rice which may require a longer duration to develop. Our outcomes evaluation had to end at 10 weeks as the semester was going into vacation period and it was logistically more feasible for OCA to start implementing the HDP at control centers during the vacation period.
The outcome data may be influenced by social desirability biases as the food diaries were self-reported. Post-intervention total energy intake per day reported by both intervention arms were higher than pre-intervention intakes reported. This could have been due to more frequent reminders sent from our study team to participants to report all foods consumed out-of-home during post-intervention. We assessed the uptake of lower-sodium salt-prepared dishes but did not examine the impact of these dishes on the participants’ sodium intake as we were uncertain about the precise amounts used by the vendors. A large increase in proportion of consumers having at least one healthier oil blend prepared dish in the control arm was observed post-intervention. This observation might have been due to contamination. Although we tried to limit contamination by selecting participants who were frequent diners at a given food centre, it is possible that motivated participants from control centers may have switched to eating at the intervention centers due to availability of healthier food options. However, this would result in an underestimation of the intervention effects. As with other dietary worksite interventions (53), we did not assess the change in frequency of healthier dishes or quality of dishes taken at home for comparison with the dietary behaviour at school/work. As during pilot testing, we found that respondent burden for recording all foods consumed was high which could potentially increase drop-out. Hence any compensatory actions taken at home (e.g. preparation of healthier home-made dishes) could not be assessed.