The right foods can prevent you from getting sick and help you recover quicker if you do fall ill. Here's how to build a strong immune system and help your body fight off the bad guys.

You got sneezed on in the subway. Coughed on in the coffee shop. Your colleagues keep coming to work when they should be calling in sick. And your kids are bringing home illnesses you never even heard of. How the heck are you supposed to stay healthy?

It might seem like seasonal illness is out of your control. And, yeah, sometimes, sick happens. But you have more power than you think.

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Your immune system is an incredible thing. The bacteria in your gut is actually a powerful army willing to fight on your behalf, but only if you feed them properly. And if you do get sick, certain foods can help you recover quicker. What you eat today can determine whether or not you get sick tomorrow.

Here's how to build a strong immune system and help your body fight off the bad guys.

The immune system is your best line of defense.
OK, gang, it's time to layer on the armor and bolster our defenses. (And I'm not just talking about scarves and winter coats, though those are probably good to have around too.) To stay healthy, energetic and sick-day-free, we have to strengthen our immune systems.

Here's how the immune system works: Our body's battle for immunity begins in the mouth. Bet you didn't know that your saliva contains powerful antimicrobials like lysozyme, alpha-amylase and lactoferrin.

Any germs that sneak past those will confront our stomach's hydrochloric acid.

Then, should they survive, they'll go up against the proteins and chemical compounds in our digestive system that break down bad bacteria.

Finally, our own personal good bacterial population goes to work. They prevent bad bacteria from entering our bloodstream or taking root in our small intestine and colon. Those good bacteria are called probiotics. Think of them as an army against illness.

Feed your bacteria army.
The GI tract comprises over 70 percent of the immune system. That's home to our good gut bacteria, which fight off a whole lot of yucky stuff.

If you want those bacteria to work for you, you've got to feed 'em. They love to chow down on nutrient-dense, fiber-rich whole foods. But processed foods, fats and sugars? Not so much. That's why a balanced whole-foods diet is your best insurance against all kinds of viruses and infections.

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In other words, if your diet is lousy, you'll get sick more often and stay sick for longer. Eating poorly while you're sick will only make you sicker. Good nutrition, on the other hand, enables your body to deliver a swift roundhouse kick straight to those germy invaders.

Prebiotics and probiotics.
Want a ready-to-roll squadron of healthy bacteria? Here's how to keep the soldiers well fed.

Prebiotics (aka bacteria food) help nourish our good microbial friends. Essentially, prebiotics are a form of semi-digestible fiber. You should get at least two to three servings of prebiotic-rich foods each day (more if you're unhealthy and need extra support from your gut flora).

Some of the best whole-food sources of prebiotics are:

* Vegetables: asparagus, garlic, Jerusalem artichokes, leeks and onions
* Carbs: barley, beans, oats, quinoa, rye, wheat, potatoes and yams
* Fruits: apples, bananas, berries, citrus fruits, kiwifruit
* Fats: flaxseed and chia seeds

You can also take a prebiotic supplement. Just remember, supplements are exactly that -- an addition to the real foods you're eating, not a replacement for them.

Meanwhile, probiotics (the bacteria themselves) help us stay healthy and recover faster once we get sick.

If you're healthy, aim for one to two servings of probiotic-rich foods each day (more if you are trying to prevent or alleviate a medical problem).

Some of the best whole-food sources of probiotics are:

* Dairy: yogurt, cheese and kefir with live and active cultures
* Fermented vegetables: pickles, sauerkraut, kimchi
* Fermented soy: miso, tempeh
* Miscellaneous: soy sauce, wine, kombucha

You can also take a probiotic supplement to give your healthy gut bacteria an extra helping hand -- just check with your doctor first. Eating lots of prebiotics and probiotics will help you fight off viruses and bacterial infections. But even the healthiest diet can't protect you from every invader. Sometimes we just get sick.

How to get un-sick.
We've been told a million times there's no cure for the common cold. But is there a way to at least speed up recovery when we're sick? As a matter of fact, there is. Certain foods can help you kick that crummy feeling quicker. For example:

* Garlic: It acts as an antibiotic and lessens the severity of colds and other infections.

* Chicken soup: Yep, chicken soup actually works. It provides fluids and electrolytes and may contain anti-inflammatory properties that decrease cold symptoms. You have to eat real chicken soup though -- the kind you make from simmering a chicken carcass -- not the kind from a can.

* Green tea: It boosts the production of B cell antibodies, helping us rid ourselves of invading pathogens.

* Honey: It has antibacterial and antimicrobial properties and helps suppress coughs. A few teaspoons in a cup of green tea are all you need.

* Elderberries: These have antiviral properties and are loaded with phytonutrients. Elderberry extract may reduce the duration of colds and other upper respiratory tract infections.

What about "feed a cold, starve a fever"?
Should we really fast while feverish? While there could be a degree of truth to the old saying, our bodies are complicated. Science hasn't given us a firm, one-size-fits-all answer yet.

Here's all you really need to know: Listen to your body. Our own appetite cues probably give us the clearest picture of what we should eat (or avoid eating) when we're sick.

For example, very few of us want to eat when suffering from influenza or gastroenteritis. That's because flu-like bugs and bacterial infections create inflammation that leads to appetite suppression. So, if your body's telling you not to eat, you should probably listen.

What are you eating most of the time?
It's cool to think about the power of specific foods, but if you really want to give your immune system a boost, consider how you eat most of the time. For example:

* How much are you eating? Consistently over- or undereating could compromise how the immune system responds to invaders. If your diet is broken, it's time to fix it.

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* What's your fat intake like? Chowing down on an abundance of fats (especially saturated fats and omega-6 fatty acids) could harm your gut and compromise your immune system. On the other hand, a moderate intake of healthy fats, such as nuts, olive oil and avocados, can supply a good source of vitamin E, which may help minimize your risk of influenza and respiratory infections.

* Hooked on sugar? Added sugars and high-glycemic-load diets may reduce white blood cell function and encourage inflammation, damaging your overall immune system.

* Getting enough protein? On the other hand, dietary protein insufficiencies and/or depletions in iron and zinc may lower overall immunity. In general, one palm-size portion of protein for women and two palm-size portions for men should be included at each meal.

* Are you eating the rainbow? Lots of fruit and vegetables are needed to get the vitamins and minerals your immune system needs. That includes iron, zinc, magnesium, manganese, selenium, copper, folic acid and vitamins A, C, D, E, B6 and B12. So, boys and girls, do what your mother told you and eat your veggies.

Remember: An overall, healthy balanced diet that supports your immune system is your best bet to avoid getting sick in the first place.