Educator response: the science behind the headline

Welcome to Week 2 when you’ll be considering the biases we bring to what we read and gain a perspective on the factors that influence how journalists present scientific evidence. By the end of the week you’ll know how to refer back to the original research, how to interpret scientific terms and make sense of statistics.

Here is a full analysis of the scientific paper you investigated in Step 1.13. You may like to compare your answers with our conclusions but please note we’ve provided a far more in-depth analysis than we asked you to complete.

What kind of study was this?

This is a systematic review, based on a meta-analysis which pooled the results of all available observational studies to investigate the associations between diet and depression.

What were the study’s main results and conclusion? (additional comment from the Educator)

The main results showed 1) the Mediterranean diet was associated with a lower incidence of depression by including four longitudinal studies; 2) Dietary Inflammatory Index was associated with a lower incidence of depression in four longitudinal studies.

The author concluded ‘a healthy diet, particularly a traditional Mediterranean diet and avoiding a pro-inflammatory diet, is associated with reduced risk of depressive symptoms or clinical depression’. The author also concluded (in the ‘Conclusions’ section) that 1) with the problem of reverse causality being acute in the context of diet and depression, there is a clear need for more prospective studies; 2) while recent intervention studies provide preliminary evidence, further clinical trials are required to validate the current results.

What were the strengths and limitations of this type of study?

As you learned in Step 1.11, this systematic review is based on a meta-analysis; a method of combining results from separate studies to draw broader, overall conclusions about a hypothesis. Although this study type provides the strongest available evidence it has several limitations, including the fact that some of the data included in the studies may be flawed. The analysis may also include data derived from different methods for measuring variables, making direct comparisons impossible.

How could we interpret and apply the current study’s results in our life? (additional comment from the Educator)

The meta-analysis pooled the results from observational studies, which resulted in several limitations, such as 1) the potential influence of other confounding factors; and 2) cause and effect can’t be proven between the diet and disease outcomes. As the authors stated, the results of this meta-analysis will require clinical trials to validate the current findings in the future. Nevertheless, having a healthy lifestyle including a healthy diet is important for your physical and/or mental health.

What’s your analysis of the headline?

The Guardian headline suggested ‘Eating junk food raises risk of depression’, but the original scientific publication investigated the link between diet quality and risk of depressive outcomes. The headline therefore oversimplified the research findings.