* Population studies typically involve tens or hundreds of thousands of people. This population study involved 702 people in Brazil – 80% of them women.
* It claimed that vegetarian and plant-based diets were associated with a lower incidence of Covid-19 than omnivore diets. There were no claims that diet made any difference to the severity or duration of Covid-19.
* There were many issues with the paper.
* The diet was self-reported. The incidence of Covid-19 was self-reported. We don't know if the self-reported Covid-19 was based on self-diagnosed symptoms or a(n unreliable) test.
* All groups in this study consumed animal foods. The term 'plant-based' diet implies vegan but there weren't enough vegans to study. Participants were divided into omnivores, flexitarians (who consumed meat up to 3 times a week and could consume unlimited fish, eggs and dairy – what I would call omnivores) and vegetarians/vegans combined (and thus a group consuming eggs and dairy).
* The usual healthy person confounder was present and very relevant to Covid-19. Those in the so-called 'plant-based' group were far less likely to be black, far less likely to be overweight or obese and far less likely to have comorbidities – all known risk factors for Covid-19. These factors were adjusted for, but we can't adjust for a completely different person.
* The claimed plausible mechanism for why those eating more plants (because eating only plants wasn’t studied) might self-report lower Covid-19 incidence did not withstand scrutiny.
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