Feeding your body certain foods may help keep your immune system strong. If you're looking for ways to prevent winter colds and the flu, your first step should be a visit to your local grocery store. Plan your meals to include these 15 powerful immune system boosters.

1. Citrus fruits

Most people turn to vitamin C after they've caught a cold. That’s because it helps build up your immune system. Vitamin C is thought to increase the production of white blood cells. These are key to fighting infections.

Popular citrus fruits include:

• grapefruit
• oranges
• tangerines
• lemons
• limes
• clementine

Because your body doesn't produce or store it, you need daily vitamin C for continued health. Almost all citrus fruits are high in vitamin C. With such a variety to choose from, it's easy to add a squeeze of this vitamin to any meal.

2. Red bell peppers

If you think citrus fruits have the most vitamin C of any fruit or vegetable, think again. Ounce for ounce, red bell peppers contain twice as much vitamin C as citrus. They’re also a rich source of beta carotene. Besides boosting your immune system, vitamin C may help maintain healthy skin. Beta carotene helps keep your eyes and skin healthy.

3. Broccoli

Broccoli is supercharged with vitamins and minerals. Packed with vitamins A, C, and E, as well as many other antioxidants and fiber, broccoli is one of the healthiest vegetables you can put on your table. The key to keeping its power intact is to cook it as little as possible — or better yet, not at all.

4. Garlic

Garlic is found in almost every cuisine in the world. It adds a little zing to food and it's a must-have for your health. Early civilizations recognized its value in fighting infections. According to the National Center for Complementary and Integrative Health Trusted Source, garlic may also help lower blood pressure and slow down hardening of the arteries. Garlic’s immune-boosting properties seem to come from a heavy concentration of sulfur-containing compounds, such as allicin.

5. Ginger

Ginger is another ingredient many turn to after getting sick. Ginger may help decrease inflammation, which can help reduce a sore throat and other inflammatory illnesses. Ginger may also help decrease nausea.

While it's used in many sweet desserts, ginger packs some heat in the form of gingerol, a relative of capsaicin. Ginger may help decrease chronic pain and may possess cholesterol-lowering properties, according to recent animal research Trusted Source.

6. Spinach

Spinach made our list not just because it's rich in vitamin C. It's also packed with numerous antioxidants and beta carotene, which may increase the infection-fighting ability of our immune systems. Similar to broccoli, spinach is healthiest when it’s cooked as little as possible so that it retains its nutrients. However, light cooking enhances its vitamin A and allows other nutrients to be released from oxalic acid.

7. Yogurt

Look for yogurts that have "live and active cultures" printed on the label, like Greek yogurt. These cultures may stimulate your immune system to help fight diseases. Try to get plain yogurts rather than the kinds that are pre flavored and loaded with sugar. You can sweeten plain yogurt yourself with healthy fruits and a drizzle of honey instead.

Yogurt can also be a great source of vitamin D, so try to select brands fortified with vitamin D. Vitamin D helps regulate the immune system and is thought to boost our body’s natural defenses against diseases.

8. Almonds

When it comes to preventing and fighting off colds, vitamin E tends to take a backseat to vitamin C. However, vitamin E is key to a healthy immune system. It’s a fat-soluble vitamin, meaning it requires the presence of fat to be absorbed properly. Nuts, such as almonds, are packed with the vitamin and also have healthy fats. A half-cup serving, which is about 46 whole, shelled almonds, provides nearly 100 percent of the recommended daily amount of vitamin E.

9. Turmeric

You may know turmeric as a key ingredient in many curries. But this bright yellow, bitter spice has also been used for years as an anti-inflammatory in treating both osteoarthritis and rheumatoid arthritis. Also, researchTrusted Source shows that high concentrations of curcumin, which gives turmeric its distinctive color, can help decrease exercise-induced muscle damage.

10. Green tea

Both green and black teas are packed with flavonoids, a type of antioxidant. Where green tea really excels is in its levels of epigallocatechin gallate, or EGCG, another powerful antioxidant. EGCG has been shown to enhance immune function. The fermentation process black tea goes through destroys a lot of the EGCG. Green tea, on the other hand, is steamed and not fermented, so the EGCG is preserved.

Green tea is also a good source of the amino acid L-theanine. L-theanine may aid in the production of germ-fighting compounds in your T-cells.

11. Papaya

Papaya is another fruit loaded with vitamin C. You can find 224 percent of the daily recommended amount of vitamin C in a single papaya. Papayas also have a digestive enzyme called papain that has anti-inflammatory effects.

Papayas have decent amounts of potassium, B vitamins, and folate, all of which are beneficial to your overall health.

12. Kiwi

Like papayas, kiwis are naturally full of a ton of essential nutrients, including folate, potassium, vitamin K, and vitamin C. Vitamin C boosts white blood cells to fight infection, while kiwi’s other nutrients keep the rest of your body functioning properly.

13. Poultry

When you’re sick, chicken soup is more than just a feel-good food with a placebo effect. It helps improve symptoms of a cold and also helps protect you from getting sick in the first place. Poultry, such as chicken and turkey, is high in vitamin B-6. About 3 ounces of light turkey or chicken meat contains 40 to 50 percent of your daily recommended amount of B-6.

Vitamin B-6 is an important player in many of the chemical reactions that happen in the body. It’s also vital to the formation of new and healthy red blood cells. Stock or broth made by boiling chicken bones contains gelatin, chondroitin, and other nutrients helpful for gut healing and immunity.

14. Sunflower seeds

Sunflower seeds are full of nutrients, including phosphorous, magnesium, and vitamin B-6. They’re also incredibly high in vitamin E, a powerful antioxidant.

Vitamin E is important in regulating and maintaining immune system function. Other foods with high amounts of vitamin E include avocados and dark leafy greens.

15. Shellfish

Shellfish isn’t what jumps to mind for many who are trying to boost their immune system, but some types of shellfish are packed with zinc.

Zinc doesn’t get as much attention as many other vitamins and minerals, but our bodies need it so that our immune cells can function as intended.

Varieties of shellfish that are high in zinc include:

• crab
• clams
• lobster
• mussels

Keep in mind that you don’t want to have more than the daily recommended amount of zinc in your diet. For adult men, it’s 11 milligrams (mg), and for women, it’s 8 mg. Too much zinc can actually inhibit immune system function.

Feeding your body certain foods may help keep your immune system strong. If you're looking for ways to prevent winter colds and the flu, your first step should be a visit to your local grocery store. Plan your meals to include these 15 powerful immune system boosters.

1. Citrus fruits

Most people turn to vitamin C after they've caught a cold. That’s because it helps build up your immune system. Vitamin C is thought to increase the production of white blood cells. These are key to fighting infections.

Popular citrus fruits include:

• grapefruit
• oranges
• tangerines
• lemons
• limes
• clementine

Because your body doesn't produce or store it, you need daily vitamin C for continued health. Almost all citrus fruits are high in vitamin C. With such a variety to choose from, it's easy to add a squeeze of this vitamin to any meal.

2. Red bell peppers

If you think citrus fruits have the most vitamin C of any fruit or vegetable, think again. Ounce for ounce, red bell peppers contain twice as much vitamin C as citrus. They’re also a rich source of beta carotene. Besides boosting your immune system, vitamin C may help maintain healthy skin. Beta carotene helps keep your eyes and skin healthy.

3. Broccoli

Broccoli is supercharged with vitamins and minerals. Packed with vitamins A, C, and E, as well as many other antioxidants and fiber, broccoli is one of the healthiest vegetables you can put on your table. The key to keeping its power intact is to cook it as little as possible — or better yet, not at all.

4. Garlic

Garlic is found in almost every cuisine in the world. It adds a little zing to food and it's a must-have for your health. Early civilizations recognized its value in fighting infections. According to the National Center for Complementary and Integrative Health Trusted Source, garlic may also help lower blood pressure and slow down hardening of the arteries. Garlic’s immune-boosting properties seem to come from a heavy concentration of sulfur-containing compounds, such as allicin.

5. Ginger

Ginger is another ingredient many turn to after getting sick. Ginger may help decrease inflammation, which can help reduce a sore throat and other inflammatory illnesses. Ginger may also help decrease nausea.

While it's used in many sweet desserts, ginger packs some heat in the form of gingerol, a relative of capsaicin. Ginger may help decrease chronic pain and may possess cholesterol-lowering properties, according to recent animal research Trusted Source.

6. Spinach

Spinach made our list not just because it's rich in vitamin C. It's also packed with numerous antioxidants and beta carotene, which may increase the infection-fighting ability of our immune systems. Similar to broccoli, spinach is healthiest when it’s cooked as little as possible so that it retains its nutrients. However, light cooking enhances its vitamin A and allows other nutrients to be released from oxalic acid.

7. Yogurt

Look for yogurts that have "live and active cultures" printed on the label, like Greek yogurt. These cultures may stimulate your immune system to help fight diseases. Try to get plain yogurts rather than the kinds that are pre flavored and loaded with sugar. You can sweeten plain yogurt yourself with healthy fruits and a drizzle of honey instead.

Yogurt can also be a great source of vitamin D, so try to select brands fortified with vitamin D. Vitamin D helps regulate the immune system and is thought to boost our body’s natural defenses against diseases.

8. Almonds

When it comes to preventing and fighting off colds, vitamin E tends to take a backseat to vitamin C. However, vitamin E is key to a healthy immune system. It’s a fat-soluble vitamin, meaning it requires the presence of fat to be absorbed properly. Nuts, such as almonds, are packed with the vitamin and also have healthy fats. A half-cup serving, which is about 46 whole, shelled almonds, provides nearly 100 percent of the recommended daily amount of vitamin E.

9. Turmeric

You may know turmeric as a key ingredient in many curries. But this bright yellow, bitter spice has also been used for years as an anti-inflammatory in treating both osteoarthritis and rheumatoid arthritis. Also, researchTrusted Source shows that high concentrations of curcumin, which gives turmeric its distinctive color, can help decrease exercise-induced muscle damage.

10. Green tea

Both green and black teas are packed with flavonoids, a type of antioxidant. Where green tea really excels is in its levels of epigallocatechin gallate, or EGCG, another powerful antioxidant. EGCG has been shown to enhance immune function. The fermentation process black tea goes through destroys a lot of the EGCG. Green tea, on the other hand, is steamed and not fermented, so the EGCG is preserved.

Green tea is also a good source of the amino acid L-theanine. L-theanine may aid in the production of germ-fighting compounds in your T-cells.

11. Papaya

Papaya is another fruit loaded with vitamin C. You can find 224 percent of the daily recommended amount of vitamin C in a single papaya. Papayas also have a digestive enzyme called papain that has anti-inflammatory effects.

Papayas have decent amounts of potassium, B vitamins, and folate, all of which are beneficial to your overall health.

12. Kiwi

Like papayas, kiwis are naturally full of a ton of essential nutrients, including folate, potassium, vitamin K, and vitamin C. Vitamin C boosts white blood cells to fight infection, while kiwi’s other nutrients keep the rest of your body functioning properly.

13. Poultry

When you’re sick, chicken soup is more than just a feel-good food with a placebo effect. It helps improve symptoms of a cold and also helps protect you from getting sick in the first place. Poultry, such as chicken and turkey, is high in vitamin B-6. About 3 ounces of light turkey or chicken meat contains 40 to 50 percent of your daily recommended amount of B-6.

Vitamin B-6 is an important player in many of the chemical reactions that happen in the body. It’s also vital to the formation of new and healthy red blood cells. Stock or broth made by boiling chicken bones contains gelatin, chondroitin, and other nutrients helpful for gut healing and immunity.

14. Sunflower seeds

Sunflower seeds are full of nutrients, including phosphorous, magnesium, and vitamin B-6. They’re also incredibly high in vitamin E, a powerful antioxidant.

Vitamin E is important in regulating and maintaining immune system function. Other foods with high amounts of vitamin E include avocados and dark leafy greens.

15. Shellfish

Shellfish isn’t what jumps to mind for many who are trying to boost their immune system, but some types of shellfish are packed with zinc.

Zinc doesn’t get as much attention as many other vitamins and minerals, but our bodies need it so that our immune cells can function as intended.

Varieties of shellfish that are high in zinc include:

• crab
• clams
• lobster
• mussels

Keep in mind that you don’t want to have more than the daily recommended amount of zinc in your diet. For adult men, it’s 11 milligrams (mg), and for women, it’s 8 mg. Too much zinc can actually inhibit immune system function.