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COVID and Evolutionary Fitness

...no amount of social justice, kindness-washing, science denial, or normalization of the obesity epidemic through social media campaigns will change the fact that obesity isn’t a lifestyle choice, it’s a disease.


by Marc Peruzzi

To a layperson, there was nothing visually novel about New York City’s COVID wards in the spring of 2020. Health care providers fully kitted up in PPE is common operating procedure in an age of antibiotic resistant pathogens. The public didn’t see the bodies piling up in makeshift morgues. At most we witnessed COVID in the gaunt and distant eyes of New York’s frontline workers; warriors from an unseen war broadcast on the evening news. 

To those ICU veterans, though, one COVID marker was unmistakable as they walked through those wards. In New York City, where only 22 percent of the population is obese, a full 37 percent of the COVID patients admitted to ICU were. Among the obese were young people. “We had teenagers on the ICU floor,” says Dr. Jennifer Lighter, an epidemiologist at NYU Hospital and the Pediatric Stewardship Director with NYU School of Medicine. “The young people that got sicker in the ICU were obese. Every teenager I cared for was obese. The most obese patients that were admitted to the hospital, those with BMIs greater than 40, were three times more likely than anyone except patients over age 80 to be placed on a ventilator.” 

At first, obesity and COVID were only linked anecdotally. Doctors saw obese patients in beds. But then New York City’s hospitals—disparate entities in normal times—morphed into one cohesive laboratory. Obesity data was sparse in Asia and Europe, but in the U.S., where that pandemic has been burning hot for 40 years and is routinely noted upon hospital admittance, the information poured in. A team of NYU researchers, including Dr. Lighter, sprang into action, tabulating data and developing artificial intelligence style “decision trees” to make sense of what was happening. The goal wasn’t to fully understand why obesity was a risk factor in COVID, the more immediate concern was simply to prove that it was. Do that quickly and lives could be saved. Within a few weeks, the researchers determined that, after old age, obesity was the single largest driver of New York City area COVID related ICU admissions and deaths.

Researchers at NYU and Johns Hopkins have already hypothesized about why the pairing of COVID and obesity is so lethal. Three broad factors are at play. The first is that the obese almost universally suffer from some form of compromised lung function. In the simplest view, this is a matter of physics. It’s more difficult to expand your diaphragm and draw in breath when you’re loaded down with belly fat. But along with the physics come other pulmonary risks like asthma, or lung capacity that’s simply diminished by a lack of aerobic exercise. And as a population, the obese—discounting sumo wrestlers and some NFL lineman—are out of shape.

The second theory is that the fat itself is at play. Fat is metabolically living tissue, rich with immune cells called cytokines. In the obese, those cytokines constantly light up in search of invader cells—both real and imagined—driving systemic inflammation during normal life. Add a novel virus like COVID to the mix and those already overreactive cells go haywire with the cytokines targeting COVID recruiting non-specific immune cells in a mustering of forces gone bonkers. The resulting immune system “storm” attacks not just the COVID virus, but the entire body. One particularly deadly fallout of this inflammation is a condition known as hypercoagulation or rampant blood clotting. Such clots lead to heart attacks, strokes, and death. Cytokine storms and hypercoagulation kill most COVID patients. 

The third hypothesis (and all three can be true simultensoulsy) is that the fat tissue in obese patients not only drives the disproportionate response of a confused immune system, but serves as a habitat for the virus. The same ACE2 receptor cells that the virus bonds with in human lungs are abundant in visceral fat. That’s almost certainly not lethal in itself—fat doesn’t breathe or beat like the lungs and heart. But if fat cells let COVID replicate, then that’s bad news for the obese. We now know that with COVID, the total viral load drove the loss of life among Italy’s (largely trim) health care workers. It’s believed they were taking in so much virus through the eyes, nose, and mouth over time that the body couldn’t mount a sustained defense. If excess body fat contributes to such an extreme viral load from within, that might help explain why Americans—the most obese people of any large nation—suffered the world’s most COVID deaths by June of 2020.

Now that we know that obesity is the second largest COVID comorbidity behind extreme old age, researchers are questioning our response to COVID. After the initial lockdown and the ramp-up in testing, telling the U.S. population to stay in their homes might have been bad advice. “Increased focus on social distancing and being more vigilant about at-risk groups might be the better way,” says NYU’s Dr. Christopher Petrilli, a lead author of that early work identifying obesity as a COVID risk factor. “People that are locked down and out of work can’t exercise or afford healthy foods. The prolonged shutdown devastated the economy—and the economy is patients.”    

As devastating as the COVID virus is to America’s obese, it’s important to remember that COVID is merely a simple organism that, like all life on earth, only exists to replicate itself. There is no malice in a virus. Killing hosts is an evolutionary dead end. The best way for the COVID virus to reproduce is to jump from host to host with more efficacy than the common cold—and apparently even fewer symptoms in most people. That is precisely why more lethal viruses like Ebola tend not to result in pandemics—so far anyway. Extreme old age is often lethal with the flu. With COVID, it’s extreme old age and obesity. But the virus doesn’t intend that lethality. It’s only intent, in Darwin’s terms, is to survive on earth at this moment in time.  

As an active and healthy reader of Mountain magazine, you might not think the connection between obesity and COVID is linked to you. And in many ways that’s true. Obesity is a disease that afflicts the poor disproportionately—indefatigable and wealthier mountain people tend to do just fine. But even in the nation’s fittest state of Colorado, obesity is on the rise. If you applied today’s obesity rates in Colorado to the national numbers a few decades ago, it would be one of the fattest states in the country. Like COVID, obesity is a public health concern that can kill millions and has the ability to threaten the outdoor recreation business. And that means we all need to do our part to fight it. That includes reminding loved ones and public officials that no amount of social justice, kindness-washing, science denial, or normalization of the obesity epidemic through social media campaigns will change the fact that obesity isn’t a lifestyle choice, it’s a disease. Also, survival of the fittest isn’t just about birds in the Galapagos. 

That message was lost when our public health officials in the Coronavirus Task Force told people to stay home in early 2020. Staying at home is not good for obesity. Instead, the task force should have been telling the nation to avoid others and get fit outdoors, because in terms of personal health and the health of the species—fitness matters.


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