Could Eating Cabbage and Fermented Vegetables Reduce Severe Outcomes of COVID-19?

During the COVID-19 pandemic you may be getting questions from your clients about how food and nutrients may help prevent or treat the coronavirus. The following analysis by a dietetic student looks at a study in adults related to eating fermented vegetables. 

 

A recent narrative review compared COVID-19 mortality rates between and within countries, with a nutrition lens (1). This review led the authors to hypothesize that the severity of COVID-19 outcomes may be reduced through the consumption of foods such as cabbage and fermented vegetables.  

 

Analysis Details
A review of two ecological studies (2,3) suggested that there was a statistically significant association between a higher consumption of cabbage, cucumber and fermented vegetables and lower COVID-19 mortality rates. While there are notable limitations to ecological research (further discussed below), it is biologically plausible that cabbage and fermented vegetables could have a protective role on COVID-19 outcomes. The sulforaphane precursors found in cabbage and the Lactobacillus found in fermented vegetables both activate the nuclear factor (erythroid-derived 2)-like 2 (Nrf2), a regulator of cellular anti-oxidative response (4-6). Nrf2 has been shown to protect against many of the factors that increase the risk of severe COVID-19 outcomes, including insulin resistance, inflammation and endothelial damage (7,8). Microbiome changes of the gut resulting from live bacterial cultures in fermented vegetables might also provide protective measures against COVID-19, although further studies are needed to prove whether this is the case (9,10). 

 

A few limitations must be considered when analyzing this article. First, the authors did not perform a robust systematic review with risk of bias assessments, given the lack of original research on the topic. Additionally, the hypothesis of this review relied heavily on data from two ecological studies (2,3), making ecological fallacy a concern. While data compiled through ecological studies can be useful in showing possible associations between variables, results may be misinterpreted for a number of reasons. Most notably, data used for ecological studies comes from populations, rather than individuals, and as such, may have been impacted by a large number of possible confounding factors. For example, COVID-19 mortality rates could be confounded by location-specific factors such as the pandemic policies in place within each country (11), proportion of frontline workers (12) or levels of chronic disease within the population (13). Furthermore, the two ecological studies (2,3) supporting the hypothesis are preprints and therefore have not yet undergone peer review.

 

Bottom Line
The authors acknowledged that this review was intended to generate hypotheses for future studies. Further research is needed to determine if the consumption of cabbage, cucumber and fermented foods can reduce the severity of outcomes resulting from COVID-19.