Your immune system is always chugging away, defending you from bacteria, viruses, and other germs and protecting you from everything from common colds to cancer. While no one food will magically fight off the flu, adding these foods to your day will give your immune system a fighting chance through cold season and beyond.

Before we get to the day to day what to eat, what should you do if you feel a cold coming on NOW?

The latest and greatest research states that taking 8 grams of vitamin C a day starting at the first signs of a cold will reduce its length and 80 mg/day of zinc acetate lozenges may cut the length of your cold by more than half. So grab those first and then read on!

Immunity Boosting Foods

Garlic: Garlic everyday keeps the doctor away! British researchers found that people who had garlic everyday for 12 weeks were two thirds less likely to catch a cold! Allicin, an active ingredient, was credited for garlic’s potent powers. Pro tip: In order to get the most bang for your bite, let crushed or chopped garlic sit for 10 minutes before cooking, which allows enzymes to create more flu-fighting allicin. If you have a stomach (and mouth) of steel, try eating garlic raw. You can also find ways to add raw garlic into your diet, like in salsa, hummus, or salad dressing, or roast whole heads of garlic. Pop directly in your mouth or smear over whole grain bread for a delicious snack.

Yogurt: Your gut contains - wait for it - ten times more cells (in the form of bacteria) than are in the rest of your entire body. Researching this complex “microbiome” in each of us is currently all the rage. While the bacteria in our gut help us break down food and provide some vitamins, it has also been found that they affect everything from hunger, how fat in our diet affects weight gain, and even our immune systems. One study found that people who had yogurt daily took a third less sick days than those who didn’t. Due to processing, not all yogurt is high in probiotics, so look for the "Live & Active Cultures" logo to ensure you're getting a healthful boost.

Brazil Nuts: Just one of these nuts provides all the selenium you need each day. This nutrient is necessary for the production of white blood cells and proteins that help immune cells communicate with one another. Love oysters? Selenium is also especially high in shellfish.

Tea: According to a Harvard study, drinking tea boosts the immune system’s messengers, interferons, by tenfold, allowing for a speedy reaction time when you encounter harmful invaders like bacteria, viruses and even tumor cells. Luckily the amino acid responsible for tea’s immune boosting abilities, L-theanine, is in decaf tea, too, since it takes 5 cups of black or green tea to get these results. To get an even bigger boost, researchers at Purdue found that adding a splash of lemon helps increase the amount of antioxidants the body can absorb.

Oats, Barley, Mushrooms and Seaweed: What do all of the above have in common? Beta-glucans. This type of fiber has been found to help activate macrophages and natural killer, white blood cells that gobble up and kill invaders. Thanks to this boost in the immune system, beta glucans have been linked to reducing the length of the flu.

Stand Out Nutrients

Protein: Protein forms the building blocks of all the body's cells, including the cells and antibodies that make up your immune system. When the body is deficient in protein it cannot make these immune boosting cells. To find your optimal intake, take your weight and divide by 2.2 (to convert to kilograms). Multiply this number by 0.8 and 1 to find your daily range of protein.
Best sources: Try a wide variety of lean, high quality protein sources, like low-fat meats, seafood, poultry, eggs, beans, nuts and seeds.

Vitamin A: This fat-soluble vitamin helps regulate the immune system. It also keeps our first barrier between us and the outside world - our skin, and the surfaces that line the mouth, stomach, intestines and respiratory system - healthy so they can keep out invaders. While it’s important to get enough vitamin A, it can also be easy to get too much of a type of vitamin A, retinol, if your main sources are supplements and fortified foods. A healthier bet is to eat real foods that contain substances the body can convert to vitamin A, like beta carotene. Bonus, these real foods also tend to have other healthy goodies for your bod - and your immune system, like vitamin C and fiber.
Best Sources: Sweet potatoes, carrots, kale, spinach, red bell peppers, apricots, eggs, and cantaloupes.

Vitamin C: You’ve probably heard that vitamin C is good for colds, but why? Vitamin C is used by various white blood cells - phagocytes (which eat invaders) and t-cells (which help destroy pathogens or make antibodies.) Not only is it important to get enough vitamin C to keep your immune system fending off attacks, but new research shows that the duration of the common cold can actually be shortened by taking large doses of vitamin C. The researchers suggest taking 8 grams of vitamin C at the first signs of a cold.
Best Source: Citrus fruits (like oranges, lemons), red bell pepper, strawberries, kiwis, and dark leafy green vegetables.

Zinc: It’s estimated that about 12% of Americans and 40% of older Americans are deficient in this important nutrient, which is essential for the development and activation of the white blood cells that help destroy invading bacteria and viruses and make antibodies. Even a minor deficiency may up your risk for infection. Zinc deficiency is even more common in vegetarians, since vegetarian zinc sources are harder to absorb. If eating more meat isn't an option and you’d like to up your zinc intake, soak beans and grains to reduce zinc-snaring phytates. If you take mineral supplements, try taking them at a different time of day than when you’re eating zinc rich foods or supplements as they can compete for absorption. And if you feel a cold coming on now? New research has found that getting 80 mg/day of zinc acetate lozenges through the duration of a cold can increase your recovery rate by three times!  
Best Sources: Red meat, poultry, pork, seafood (especially oysters), beans, nuts, whole grains, fortified cereals and dairy products.