Obesity and the Flu: Five Questions with Bariatric Surgeon Dr. Francisco Guzman

2D digital illustration made from hand drawn elements depicting viruses.

Skies are gray, the weather can’t seem to make up its wintery mind, and we’re in the throes of flu season. In recent years, we’ve seen several studies digging deeper into the link between a more severe flu response in people with obesity. We sat down with bariatric surgeon Fransciso Guzman, MD, to learn what that means.

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Will you provide some background on how obesity can affect your body’s response to the flu?

Obesity has been identified as an independent risk factor for a whole host of complications, especially in the setting of other illnesses. Meaning that because obesity is a pro-inflammatory state it plays a negative role in how our immune system fights off or responds to infections, and respiratory viruses are no exception.

Why does that pro-inflammatory state have such a negative impact on our immune system?

Normally, we have two immune systems—an innate one and an adaptive one. Obesity impacts both. The innate one is the first line of defense, especially after new viruses that the body hasn't encountered, like the flu. Each flu season it's been shown that these interferons or proteins that help the body fight off infections are not as well-expressed in obesity. Also, the number and quality of T-cells, which is the other type of cell that works in the other immune system response is also deficient. It affects all aspects of infection; you would be shedding the virus for a longer period of time too.

Does that also affect the efficacy of the flu vaccine?

It affects everything immune-related. Obesity impairs your immune response to the flu and to the flu vaccine as well because of that pro-inflammatory state. So, you have a higher risk of being admitted to the hospital and higher chances of requiring ICU admission or even death. After your body crosses that threshold of BMI 30 or more, then it just increases proportionately. The heavier you are, the higher the risk.

Is the BMI threshold basically an indicator of that pro-inflammatory state? Does it happen over time as weight is gained?

The cutoff that has been used to establish this heightened risk is broken down into the obesity classifications that we normally think of, BMI 30, 35, 40, 45. The way research established that risk is after BMI 30, that risk starts to creep up. They found that after a BMI of 30, the risk of hospitalization increases, especially after 40, the risk of ICU admission is greater, and the risk of death is greater. But how that is manifested at a molecular level, how those changes are evolving along the spectrum, I don't think we know that.

What’s your advice for people as they navigate flu season? 

I just want to reinforce what we already know: the best way to protect everyone is to get vaccinated. That's the only thing that has been shown to help. The thinking used to be that independent risk factors for serious outcomes after the flu were just people with diabetes or people with heart disease. And because the great majority of patients with obesity have both of those things, they thought it wasn't the obesity itself. 

However, it's been shown that patients with obesity without cardiovascular disease and without diabetes also have a higher risk of complications. So, obesity is just a compilation of risks, just as it is for the patient with cardiovascular disease, the patient with diabetes. The only way to address that or try to mitigate that risk is through vaccination. Because you can't really fix obesity overnight, the only thing you can do is still vaccinate.


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