When it comes to practical and nutritious snacks, you can’t ignore apples. It’s a filling option that you can take with you when you get out of the house to do things, or toss in your lunch bag to work.

So is an apple a day really that useful? There is no official statement that exists where the statement shows specifically about the effects of this fruit on the body and health.

But a 2015 study confirmed that a minority of adults who lived a healthy lifestyle and consumed apples appeared to need fewer prescriptions than others.

Would you rather enjoy this fruit whole, slice it with almond butter, or add it to your salad? All are equally good for your health. You may want to know some of the following unwanted side effects that apples can have on your immune system. So here are some of the wonders, benefits and surprising side effects that this little fruit has on your immune system.

1. Quercetin in apples helps keep inflammation under control
Apples are a rich source of phytochemicals such as quercetin, which is known for its antioxidant and anti-inflammatory effects that help regulate the body’s immune response. This is the essence of how it works.

Free radicals not only damage your body’s cells, they also activate genes that trigger an increased inflammatory response. Chronic inflammation is linked to many serious illnesses and health problems, but fortunately, studies have shown that quercetin can reduce markers of inflammation.

Red apples, in particular, appear to be high in flavonoids. Also, don’t peel your apples or you’ll miss out on these health benefits—because quercetin is exclusively found in the skin.

But quercetin is not the only antioxidant that apples contain. Apples also contain a number of other flavonoids, such as catechins, epicatechins, procyanidins, phloridzin, coumaric acid, chlorogenic acid, and gallic acid, which have inflammatory and immune system benefits.

In fact, when compared to other popular fruits, apples have the second highest level of antioxidant activity and the highest proportion of free phenolics.

Research has shown that these types of phytochemicals regulate inflammatory and immune responses, while protecting the body from oxidative stress. Keep in mind, though, that the flavonoids in apples are mostly concentrated in the skin and tend to be higher in dark red varieties.

2. Pectin in Apples Supports Gut Health
Did you know that most of your immune system is located in the digestive tract? That means that keeping your microbiome healthy and balanced is key to ensuring your body is ready to fight infection.

Apples can help support gut health because they provide a certain type of soluble fiber called pectin. One 2010 study found that when women ate two apples a day, they increased the good bacteria in their gut in just two weeks.

According to a 2019 study published in Frontiers of Microbiology, one apple contains nearly 100 million bacterial cells. It should be noted that the study also found that organic apples appeared to have an advantage over conventionally grown apples, as organic apples offered a greater variety of bacteria.

It’s no secret that vitamin C is one of your body’s best defenses when it comes to warding off colds and other ailments. However, what you may not realize is that vitamin C plays many different roles in boosting your immune system.

3. Fiber in Apple Turns Immune Cells Into Anti-inflammatory
Studies have shown that simply by consuming more vitamin C, you can increase the levels of antioxidants in your blood by 30% and in turn, this can help your body’s defenses to prevent inflammation.

A 2017 review published in the journal Nutrients found that vitamin C also strengthens the epithelial barrier against pathogens and protects your cells against environmental oxidative stress.

One large apple contains about 10.3 mg of vitamin C, which may not be a lot, but apples provide 11.4% of your RDA. Plus, research also reveals that the antioxidant activity in one serving of apples (100 grams) is equivalent to 1,500 milligrams of vitamin C.

If there’s one thing apples have, it’s fiber. One medium apple offers 4.4 grams to 25 grams of fiber. So, what does that have to do with your immune system? A 2010 University of Illinois study found that the soluble fiber found in apples changes the “personality” of immune cells from pro-inflammatory to anti-inflammatory.

In fact, the mice fed the soluble fiber were only half as sick as the other group and recovered 50% faster after the scientists induced the disease in all of them.

One study claims that the reason for this effect is that soluble fiber triggers increased production of an anti-inflammatory protein called interleukin-4.