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Surprising Side Effects Fast Food Has on Your Immune System, Says Science

Is it all bad? We take a look at the research.
FACT CHECKED BY Kiersten Hickman

Good things don't come easy: Irma Thomas sang about it in the 1960s, and it's been common knowledge ever since. Fast food is perhaps the least complex way to consume calories on any given day. It tracks, then, that the burger-and-fries diet can't be "good"— it's simply too easy. This is more than just hearsay or a hunch, though. Studies have warned about the negative effects fast food has on the brain and mental health, and we've written extensively about the negative effects a quick fast-food meal can have on all parts of your body, from your skin to your waistline.

In today's especially infection-averse world, it makes sense to consider how fast food might affect another aspect of a person's well-being: the immune system. We dissected a couple of compelling studies on the topic and found that, yes, fast food is ultimately harmful to the immune system. But it's a little more complicated than that. Here's what you need to know, and if you're looking for quick meals that aren't from the drive-thru, check out our list of 100 Easiest Recipes You Can Make.

Your body reacts as if fast food is a bacterial infection.

fast food

In 2018, the University of Bonn ran a now-somewhat-iconic study exploring fast food and the immune system. They placed a group of mice on what they determined to be a "Western" diet: high in fat, high in sugar, and low in fiber. Essentially, a model for fast-food "nutrition."

After one month, they found that the animals' immune systems were having an interesting reaction. They'd "developed a strong inflammatory response throughout the body." The study compared this response to the way your immune system would react after being infected with "dangerous bacteria."

Also, did you know Fast Food Can Be as Addictive as This Illegal Drug?

Over time, fast food makes your immune system more aggressive.

fast food and chips

The longer a body is exposed to unhealthy food, the more aggressive the immune system will become. This sounds like it might be a good thing—who wouldn't want a powerful immune system that's ready to go to bat? But that system isn't meant to be in a constant state of intense activation, and when it is, it completely reprograms.

Speaking of, These Foods Can Weaken Your Immune System, Say Experts.

The immune system doesn't regulate when the fast-food intake stops.


The study went on to show that once the immune system develops this response to fast food, there's no turning back. When the mice returned to their low-fat diets (i.e. "quit fast food"), their inflammation levels did drop, but the way their immune cells had been reprogrammed stayed the same.

"It has only recently been discovered that the innate immune system has a form of memory," said professor Dr. Eicke Latz, director of the Institute for Innate Immunity of the University of Bonn, in response to the study. "After an infection, the body's defenses remain in a kind of alarm state, so that they can respond more quickly to a new attack."

Here are Instant Ways to Reduce Your Inflammation, According to a Doctor.

This response is linked to diabetes and cardiovascular disease.


The University of Bonn study linked the inflammatory immune response to conditions like type 2 diabetes and cardiovascular diseases.

"These long-term changes may be involved in the development of arteriosclerosis and diabetes, diseases linked to Western diet consumption," reads the statement on the study.

So while we always knew fast food was unhealthy, the way it messes with your immune system could make it even more dangerous than expected.

Fast food could make your immune system weaker.


In the name of presenting both sides, we also looked into a few studies that show a connection between high sugar consumption and a suppressed immune system.

Considering fast food is largely sugar and refined carbohydrates, which your body processes as sugar, there is an argument that your trip to the drive-through could actually be weakening your immune system. One doctor stated in an article published by Piedmont Healthcare, "the next time you reach for junk food, realize that you not only are affecting your weight, but you may be letting down your resistance to bacteria, viruses, and parasites."

Either way, the connection between fast food and your immune system is clear: the happy meal does not make for a happy immune system.

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Kaley Roberts
Kaley Roberts is a food writer. Read more about Kaley