This week: Three years into the pandemic, the link between Covid and BMI is still tenuous, and the science still shaky .

March 27, 2023

In this week’s episode of Rethinking Wellness, religious-studies scholar and author Alan Levinovitz (Natural and The Gluten Lie) joins us to discuss the problems with framing eating and wellness practices as “natural,” the weird parallels between gun culture and wellness culture, the tricky balance between empathizing with why people are driven to harmful wellness practices and being clear in calling out misinformation, the need for nuance when discussing the connection between physical and psychological issues, and more.

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And now for this week’s first question. Just a content note (CN) that there are “o-words” in the question and my answer, which is unfortunately sometimes unavoidable when talking about research (though it’s in the context of a critical analysis of that research). The same CN goes for all studies linked below.

Thanks, Rachel, for that great question. Before I answer, just my standard disclaimer:

These answers are for informational and educational purposes only, aren’t a substitute for individual medical or mental health advice, and don’t constitute a provider-patient relationship.

I’ve been meaning to do an update about the science on Covid and weight, and your question comes at a good time—as it happens, a new study just came out last month that is the best research I’ve seen to date about this question.

I say it’s the best because of its rigorous design: it’s a type of study called an “umbrella review,” which analyzes all the results from systematic reviews and meta-analyses (SR-MAs) on a given topic. SR-MAs are themselves reviews of all the studies that exist to date on a particular research question, and as such they’re considered one of the best forms of scientific evidence. But a significant limitation of SR-MAs is that poor-quality primary studies can lead to a poor-quality synthesis (aka “garbage in, garbage out”). Umbrella reviews can be a powerful way to cut through that noise, if they’re conducted well and critically examine the quality of the evidence according to established guidelines, which this umbrella review does.

It reviewed a total of 24 SR-MAs on the association between “obesity” and mortality in patients with Covid-19 and found that two-thirds of them were of “critically low quality” and another 29 percent were of “low quality.” A staggering 83 percent of the reviewed SR-MAs had “very low” certainty of evidence.

Only one systematic review and meta-analysis was of “moderate quality”—and that one found no significant link between high BMI and mortality.

In other words: The best available evidence to date does not show a link between higher weight and Covid death.

The researchers attribute the overall dismal showing of the reviewed SR-MAs to the “rushed” nature of systematic reviews in a pandemic, which is understandable when the need for scientific evidence is pressing and immediate. This has been true of systematic reviews during Covid-19 in general (not just about body size), the researchers explain.

But when flawed science helps drive a misinformed narrative that higher weight definitively increases the risk of Covid mortality, it creates unnecessary panic and helps perpetuate anti-fat bias.

So there isn’t actually good evidence that higher weight is linked to a greater risk of death from Covid, but what about disease severity? Are higher-weight people more likely to be hospitalized for Covid, admitted to the ICU, or given mechanical ventilation?

Probably not, recent research suggests.

As a very large observational study published earlier this year found, “obesity alone does not increase the risk of worse clinical outcomes after COVID-19 infection.” Among more than 55,000 patients who tested positive for Covid, the researchers found that higher-weight patients didn’t have an increased risk of hospitalization, ICU admission, mechanical ventilation, or death when controlling for high blood pressure and diabetes—two conditions that are independently associated with worse Covid outcomes, regardless of body size.

In fact, the researchers found, if anything higher BMI may help reduce risks: “obesity without comorbidity is associated with a lower risk of ICU admission, mechanical ventilation, and mortality in comparison with patients of normal weight,” they write (emphasis mine).

A 2021 study of roughly 250 people also may suggest a protective effect from higher weight. Like the 2023 study, it found that “obesity” wasn’t associated with an increased risk of hospitalization for Covid—and when the researchers controlled for “cardiorespiratory fitness,” higher BMI was linked to lower risk (though they acknowledge that this finding may not be generalizable beyond the study population, which only included people “who were able to perform an exercise stress test on a treadmill.”)

I’ll be on the lookout for any umbrella reviews of studies on Covid severity and BMI, which may be able to provide more insight. But there’s enough evidence to at least warrant serious skepticism of the popular belief that high BMI increases Covid severity. As is often the case with these kinds of apparent associations, there can be other things at play (like preexisting disease, or fitness, or weight-biased medical care) that account for the perceived link.

I hope that’s helpful in thinking through your response to this commercial, Rachel, and thanks again for the great question.

Bonus question: It feels a little like cheating to include this question, but several people have asked it now, so I thought I’d answer:

Thanks so much for your kind words! YES, The Wellness Trap will definitely be released as an audiobook, and yours truly is the narrator :) You can preorder it on Audible, Audiobooks.com, or other fine audiobook retailers.

​Ask your own question about anything related to diet and wellness culture (including non-food-related wellness trends) for a chance to have it answered in an upcoming edition of the newsletter or podcast.

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Here’s to thinking critically about the evidence,

Christy

P.S. Don’t miss my conversation with Alan Levinovitz, religious-studies scholar and author of Natural and The Gluten Lie, on Rethinking Wellness. We discuss the problems with framing eating and wellness practices as “natural,” the weird parallels between gun culture and wellness culture, the tricky balance between empathizing with why people are driven to harmful wellness practices and being clear in calling out misinformation, and more.

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