A small pilot study examines the reduction in the consumption of ultra-processed foods among patients with depression

This study provides new insights into the possible link between the consumption of ultra-processed foods and mental health, in this case amongst people with depression. Unlike previous studies, which have mainly observed an association between higher consumption of ultra-processed foods and an increased risk of depression, this study assesses what happens when consumption is reduced in people who already have this disorder.

The results show that during the period in which consumption of ultra-processed foods was reduced, participants reported lower scores for symptoms of depression and anxiety than during the period in which they followed their usual diet. Furthermore, the intervention was well received by the participants, although reducing their intake of these foods to such a significant extent was not particularly easy.

The study involved 20 people with depression and a high intake of ultra-processed foods. Throughout the study, participants alternated between their usual diet and a diet in which the consumption of ultra-processed foods was considerably reduced, whilst keeping other factors such as medication, therapy, exercise and sleep unchanged.
These results are interesting because they suggest that diet may play a complementary role in the management of depression. However, they should be interpreted with caution. This is a pilot study with a very small sample size, and changes in symptoms of depression and anxiety were not the primary objective of the study. Furthermore, it does not allow us to determine whether the results are specifically due to the reduction in ultra-processed foods or to other associated dietary changes, such as alterations in calorie, fat or sugar intake. Larger studies will therefore be needed to confirm these findings and gain a better understanding of the mechanisms involved.

This study provides new insights into the possible link between the consumption of ultra-processed foods and mental health, in this case amongst people with depression. Unlike previous studies, which have mainly observed an association between higher consumption of ultra-processed foods and an increased risk of depression, this study assesses what happens when consumption is reduced in people who already have this disorder.

The results show that during the period in which consumption of ultra-processed foods was reduced, participants reported lower scores for symptoms of depression and anxiety than during the period in which they followed their usual diet. Furthermore, the intervention was well received by the participants, although reducing their intake of these foods to such a significant extent was not particularly easy.

The study involved 20 people with depression and a high intake of ultra-processed foods. Throughout the study, participants alternated between their usual diet and a diet in which the consumption of ultra-processed foods was considerably reduced, whilst keeping other factors such as medication, therapy, exercise and sleep unchanged.
These results are interesting because they suggest that diet may play a complementary role in the management of depression. However, they should be interpreted with caution. This is a pilot study with a very small sample size, and changes in symptoms of depression and anxiety were not the primary objective of the study. Furthermore, it does not allow us to determine whether the results are specifically due to the reduction in ultra-processed foods or to other associated dietary changes, such as alterations in calorie, fat or sugar intake. Larger studies will therefore be needed to confirm these findings and gain a better understanding of the mechanisms involved.

The study published in JAMA Psychiatry by Chagwedera et al. as a Research Letter is a crossover trial conducted on 20 people diagnosed with depression (Patient Health Questionnaire-9 >=5), who had a high intake of ultra-processed foods (UPFs) and at least one metabolic problem (excess weight, dyslipidaemia, insulin resistance or hypertension), and in which the intervention consisted of removing UPFs from the patients’ diets. The results show that 19 participants completed the intervention, reducing their UPF intake on average, whilst also experiencing a reduction in symptoms of depression and anxiety. Another interesting finding from the study was the modest ease with which UPFs could be removed from the diet, and, consequently, the inherent difficulty of following a UPF-free diet today.

This is a small-scale study, in which the reduced symptoms of depression and anxiety were secondary analyses of the trial; the primary outcome was to assess the feasibility of the intervention, the duration of which is not specified in the main paper. Furthermore, given the outcomes studied, and despite the cross-over methodology, it cannot be entirely ruled out that part of the observed protective effect is due to a care bias, whereby participants’ levels of depression and anxiety might improve simply because they felt cared for and listened to. Nevertheless, the results are consistent with previous findings from longitudinal studies linking a higher risk of depression to higher consumption of UFP, including those from a Spanish cohort: the SUN Project (Gómez-Donoso C, et al. Eur J Nutr 2020).

For all these reasons, the suggestive findings of this study raise new questions regarding the possible mechanism linking high consumption of these products to mental health, and highlight the need to carry out further prospective studies and randomised trials to gain a better understanding of this relationship and implement appropriate preventive measures.

This is a reasonably well-designed pilot study to assess whether reducing ultra-processed foods is feasible, but it is insufficient to demonstrate that such a reduction improves depression. Only 20 people took part; the age diversity and the selected characteristics of the group limit the generalisability of the findings. The authors themselves regard the improvement in symptoms as exploratory.

The result is consistent with previous studies linking ultra-processed foods to depression and with trials suggesting benefits from improving diet. However, it does not allow us to distinguish whether the potential benefit stems from reducing the level of processing or from changes in nutrients and calorie intake.
Each participant followed both diets, in a randomly assigned order, and was asked to keep their diet and other habits consistent. This helps to control for some confounding factors, but knowing which diet one is on may influence expectations, and consumption was assessed via questionnaires.

Furthermore, recommending a change does not mean it is easy to maintain. The study does not adequately characterise participants’ financial resources, educational background or access to food and cooking facilities. Its main contribution is to justify larger trials that assess both the benefits and the feasibility of implementing the changes in everyday life. It does not yet provide sufficient grounds to recommend this intervention as a treatment for depression or as a replacement for current therapies.

This is a small-scale exploratory study that examines whether a reduction in the consumption of ultra-processed foods improves indicators of depression. The study takes the form of a ‘letter to the editor’, which means it does not carry the same weight as an original article. In this case, only the results of the depression tests for the two study groups are presented, which does not allow for an exploration of physiological explanations.

The significance of the study lies in the fact that this is the first time a clinical trial has been conducted for this purpose. Furthermore, whilst there is a wealth of scientific literature on the potential harmful effects of ultra-processed foods, the vast majority of studies are observational in nature, which do not allow for the establishment of cause-and-effect relationships. Numerous researchers have highlighted the need to carry out randomised controlled trials, such as this one, in order to determine such causality.

The study design is a crossover study, meaning that all participants consumed both proposed diets: their usual diet, high in ultra-processed foods, and the intervention diet, low in ultra-processed foods. However, the article does not mention the duration of the intervention or the system used for classifying foods and defining ultra-processed foods, which is usually the NOVA framework. Furthermore, the sample size is very small (only 19 participants completed the trial).

These limitations, along with others stated by the authors themselves in the article, mean that the study cannot be regarded as more than an exploratory piece of research, despite the fact that the results clearly show that reducing the consumption of ultra-processed foods significantly lowers the scores on the depression tests administered.

In light of these results, the appropriate course of action is to repeat the clinical trial, increasing the sample size and improving the experimental design, so that the results are more robust. In any case, although to a lesser extent, it contributes to the scientific evidence regarding the adverse health effects of consuming ultra-processed foods.

The main limitations of the study are:

• Exploratory nature: the improvement in depressive and anxiety symptoms was not the primary objective of the study.
• Unknown mechanism: the improvement cannot be linked to a reduced intake of any particular type of ultra-processed food.
• Subjective measurement of consumption: the intake of ultra-processed foods was assessed via self-report, without the use of objective measures.

Furthermore, this was a small (20 participants) and open-label pilot study; consequently, the results should be regarded as preliminary and should serve to generate new hypotheses. Therefore, intervention studies with a larger number of participants and objective measures of ultra-processed food consumption are needed, which should also investigate the mechanisms involved.