Strengths and limitations
SECONDARY
There are several strengths and limitations of the study methods that should be acknowledged. First, the small sample size is a limitation, reducing the statistical power to detect an effect of the intervention on diet-related GHGEs. Second, for the intervention group, change in diet-related GHGEs could be correlated to app usage (i.e., adherence to the intervention), which was assumed equal for all participants in the intervention group, but may not be. As such, it is a limitation that there was no data on participant adherence to the intervention available, as this possible explanation for the null findings cannot be excluded. However, the null findings are more likely due to the primary aim of the intervention, as it did not encourage participants to follow a low GHGE diet per se, although considerable content was provided on reducing red and processed meat intake and increasing plant-based food intake. Finally, the presented research benefits from analysing randomized data, thus reducing the effects of confounding variables.The use of a validated FFQ to assess dietary intake is a strength. Furthermore, the FFQ included a large number of items, thus is likely to cover a considerable proportion of the diet. However, as in any study utilizing an FFQ, some limitations remain, for example the use of self-reported data and possible introduction of social desirability and/or recall bias. As such, FFQ assessments can sometimes underestimate true dietary intake. To address these limitations, missing information on portion size was added using Swedish standard values. Furthermore, any inaccuracies in assessing dietary intake are likely to occur at both baseline and 3m follow up, within both the intervention and control. Therefore, all participant dietary intake is likely subject to the same potential measurement error, thus reducing the impact of the noted limitations on the findings.In terms of assessing the environmental impact of diet as a whole, it is important to acknowledge that GHGEs constitute only one indicator of environmental impact: land use, water use, and eutrophication potential among others are also important to consider. However, based on information available for the purposes of this study, only GHGEs have been included, thus presenting a limitation to the full assessment of environmental impact of diet. Furthermore, as with any study utilizing GHGE data, there are strengths and limitations of the methods applied in determining the GHGE value of FFQ items. In this study, GHGE values were obtained from multiple secondary sources, in which different LCA studies may have allocated GHGEs differently, hence potentially introducing some error. Such differences in GHGE values for the same food item can occur due to, for example, growing and production methods, weather and soil conditions, and transport. However, two-thirds of the GHGE values in this study were determined from one source, and the GHGE values for all FFQ items are estimated to the same system boundary. This enables accurate comparisons between different items and categories. Furthermore, using an LCA to determine GHGEs provides an estimated value, rather than a precise figure. To address this limitation, where necessary, adjustments of post-farm emissions and weight changes were made to FFQ items based on Swedish-specific standards and previous Swedish literature [