Kiwi

Kiwis contain between 90 and 110 milligrams of vitamin C — more than an average orange. They are a good source of potassium, an important mineral for strong muscles and nerves, plus immune-boosting vitamin E. They are also packed with flavonoids and carotenoids — antioxidants that promote respiratory health, heart health and optimum well-being, says Suki Hertz, M.S., R.D., nutrition professor at the Culinary Institute of America. Cut kiwis in half and scoop out the flesh for a fruit salad or mash up and stir into plain yogurt.

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Papaya

Papayas are praised for their anti-inflammatory properties. They're also an excellent source of vitamin C—one medium papaya supplies 313 percent of your daily requirement, explains Hertz. Additionally, they are a great source of beta-carotene, a phytonutrient that gets converted to vitamin A in your body and keeps eyes, skin and mucous membranes moist. Have a few slices for breakfast in the morning or blend some with orange juice for a tropical smoothie.

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Ginger

If you feel a cold coming on ward it off with ginger, which can alleviate cold symptoms and clear nasal passages. It also promotes digestive health, reduces gas pains and relaxes the intestinal tract, explains Hertz. If you find yourself battling a stomach bug or winter cold, try steeping slices of fresh ginger in hot water for a soothing and healthy morning drink.

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Pumpkin Seeds

Pumpkin seeds are packed with vitamins, amino acids and minerals, including zinc. Zinc helps the immune system by acting as an antioxidant and minimizing damage to cell membranes from free radicals, explains Hertz. Pumpkin seeds are delicious alone or sprinkled in yogurt, oatmeal or cereal. For a sweet and spicy breakfast on the go, try this energy mix.

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Wheat Germ

Full of essential vitamins and fats, wheat germ, the nutrient source of the wheat grain, can help give your immune system a boost. It's also high in vitamin E, an antioxidant that helps fight inflammation, says Hertz. Sprinkle wheat germ in yogurt, oatmeal or cold cereal.

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Beets

Give your morning glass of orange juice a boost by blending it with cooked beets — just remember to strain it before serving. Packed with antioxidants and magnesium, a mineral that assists with nerve and muscle function, beets are also especially rich in folate. This B vitamin helps prevent serious birth defects and is important for women of childbearing age and for heart health, explains Hertz.

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Flax Seeds

Flax seeds are chock-full of important nutrients and minerals, including vitamin E, an antioxidant that keeps cells healthy, and alpha-linolenic acid, a vegetarian source of omega-3 fatty acids. To obtain these healthy fats, flax seeds must be ground first, explains Hertz. A coffee grinder works perfectly for this.

Famous for their nutty flavor, flax seeds can be sprinkled on yogurt, oatmeal or cold cereal. Flax oil is another option and a good way to add important nutrients to smoothies. Both flax seeds and flax oil are highly perishable and should be kept in the refrigerator for up to three months.

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Lemons

Besides being packed with vitamin C, lemons promote healthy bacteria, rather than the type that can cause viruses and colds. Hertz suggests using lemon in place of sugar and salt, both of which can weaken the immune system. In the morning, try squeezing some on fresh fruit instead of sprinkling with sugar.

Blueberries

It's no wonder blueberries are called a superfood — they have more antioxidants than any other fruit or vegetable. They are also one of the highest-ranking foods in anthocyanidins (cancer-fighting antioxidants) and are excellent sources of vitamin C, manganese and fiber, says Hertz. Start your morning with this Greek yogurt parfait, a beautiful dish that delivers a healthy mix of berries.

Eggs

Egg yolks are a good source of selenium, a powerful mineral that supports a healthy immune system. Research on eggs is proving they are not the heart-disease villains they were once thought to be, explains Hertz. The protein in the whites is of the highest value, and the yolks, although high in dietary cholesterol, are relatively low in saturated fat.

Tofu

People who don't eat enough protein tend to load up on carbs, which can increase blood sugar levels and weaken the immune system. Tofu is a complete protein and a good source of calcium and omega-3 fatty acids, all of which can strengthen the immune system, says Hertz. For a high-protein drink that's good on the go, try this quick smoothie.

Quinoa

Quinoa (pronounced keen-wa) is commonly referred to as a grain, but it's actually a seed that can be cooked. A super food, quinoa is one of the few "complete proteins" of the plant world, meaning it supplies all of the essential amino acids that are found in meat, poultry or fish, such as lysine, which helps with tissue repair, says Hertz. In the morning, swap white or whole-wheat bread with a multigrain loaf that's loaded with quinoa, bulgur and millet.

Grapefruit and Oranges

Everyone knows that citrus is chock-full of vitamin C, and it's also packed with powerful antioxidants and is low in calories, says Hertz. For a healthy breakfast that's sure to strengthen your immune system, try a fruit salad that combines three types.

Cottage Cheese

Cottage cheese contains selenium, a powerful antioxidant that can strengthen the immune system, says Hertz. To give your immune system a boost, try this breakfast parfait which combines cottage cheese with vitamin C-rich papaya and wheat germ.