Comment about the article: «Understanding of different front-of-package labels by the Spanish population: Results of a comparative study»

Dear Sir,

We have read with great interest the article entitled “Understanding of different front-of-package labels by the Spanish population: results of a comparative study”.¹ This study addresses the perception of the participants regarding the nutritional quality of certain foods by presenting 5 types of front-of-package labels.

However, we would like to comment on some methodological aspects that may benefit similar studies in the future.

This article is classified as an experimental study. While it complies with the characteristic randomization of a study of this type, we see that it lacks a control group, since all the participants were shown some type of front-of-package labeling. For this reason, it should be classified as a quasi-experimental study, since such studies do not necessarily have the two groups (experimental and control).^2,3

In addition, the material and methods section does not specify whether the participants received any prior training regarding the concepts of: “High nutritional quality”; “Intermediate nutritional quality”; “Low nutritional quality”. Therefore, the objective of the study was actually the subjective assessment of each participant, conditioned to his or her personal level of prior knowledge, beliefs and criterion. Likewise, it should have been specified whether the nutritional information was still visible at the time of the presentation of the food to the consumer without the front-of-package labelling. Alternatively the criterion by which both the participants and the investigators classified the nutritional quality of the food should have been specified.

In the case of the reference front-of-package label (Rls label), the latter is not designed to classify food according to its nutritional profile or quality, but only to report the amount of nutrients it contains. The same applies to the octagons (warning symbol), which likewise are not designed to classify the overall nutritional quality of each food, but are used to provide a warning about some component that is present in large amounts. Therefore, they should not be used to classify food according to its nutritional quality as was done in the study. We think it should have been mentioned whether the participants had already had prior exposure to the different types of labeling or had been familiarized with some of them, as this could constitute a limitation of the study, since the results may have been affected due to a better understanding of the already known front-of-package labels versus those never seen before.