What Foods are Good for My Immune System?



Your ability to interact with the world around you and remain healthy is dependent to a large extent on the healthy functioning of your immune system. Your immune system is responsible for fighting foreign invaders to your body, like pathogenic bacteria and viruses, and also for destroying cells within your body when they become cancerous. Poor nutrition has been shown to result in increased infections, to slow healing from injury and infections, and to increase susceptibility to symptoms and complications from immune system dysfunction. Science has shown that immune function often decreases as we age, and recent research suggests this decrease is also related to nutrition and may be slowed or even stopped by maintaining healthy nutrition.

Medical science has established that one of the most important factors in supporting a healthy, balanced immune system is good nutrition. Research studies show that healthy eating can help in keeping your immune system ready and capable of functioning properly when necessary. The World’s Healthiest Foods provide the kind of nutrition that supports your immune functions to their fullest, while minimizing the agents that may induce or activate your immune response when it should not be active. Let’s take a look at how the World’s Healthiest Foods support optimal immune function.

What is my immune system?

Your immune system is like a finely tuned orchestra whose purpose is to defend your body from unhealthy insults from the world around you. Like an orchestra, your immune system contains many different instruments that work harmoniously together with one goal, protecting you from foreign insults that can cause damage to your body. And, like an orchestra, the different parts of your immune system must be present, play their part at the right time, and then stop when they have completed their function. The main parts of your immune system are the immune cells, the structural barriers in your body in which the majority of these cells are localized, and the specific messenger molecules that call the cells to action or tell them to stop.

The cells of your immune system are quite varied, and include the lymphocytes, or T-cells, which fight invading molecules directly, and the B-cells, which form antibodies that can respond to invading molecules or toxins. The antibodies produced by the B-cells can bind with a potentially damaging molecule or to the surface of a virus or bacteria, thereby targeting it for removal by other immune cells. Your immune system also includes the phagocytic cells, such as macrophages and neutrophils, which remove the debris created from destroying cells and tissue at the site of an infection.

The cells of your immune system are found circulating in your bloodstream or in the lymph nodes, which are located throughout your body; therefore, the immune cells themselves are spread throughout your tissues and can travel quickly when called upon. This way, your immune system is positioned so that it can minimize the entrance into your body of foreign invaders that can cause infection and disease and can quickly respond to any invaders that do manage to gain entrance into your body.

Your immune system also relies upon specific structures in your body that provide a foundation for defense. The most important structures are the barriers between the inside of your body and the outside. These barriers keep unwanted organisms and molecules from entering your body where they can do damage. Since your skin is in contact with the outside world, it is probably not surprising that your skin is an important barrier; however, it is only one part of your defensive barrier. Your gastrointestinal tract is actually the largest barrier between you and the outside world.

Your immune system also includes molecules called soluble factors. These are molecules that can recognize when your barrier has been compromised by a foreign invader or toxin and then try to heal the area of damage and remove the insult from your body rapidly. Factors such as the complement cascade, a complex group of proteins, can form an immediate response to an insult. Your immune system also can deploy signaling molecules, which are soluble factors that send messages to the immune cells located further inside the tissue that has been compromised, or into your bloodstream. These messenger soluble factors call immune cells to the site of damage and activate the cells, bringing them in full force to the infected area. These messenger molecules are called cytokines.

Your cytokines not only signal immune cells to take up action, but they also often promote an inflammatory response. The inflammatory response at a site of infection is one way your body secludes, or walls-off, an infected area. For example, if you have ever had poison ivy, or gotten a rash from eating a food to which you are allergic, you may have noticed the signs of inflammation -- redness and swelling -- surrounding the affected area. So, when we talk about the immune system, it is not one organ; it is really the types of immune cells, structures, and soluble factors, like cytokines, which are present throughout all your organs that constitute the immune system. And, your immune system gets help from your inflammatory response.

Nutritionally supporting your immune system means supporting all these sections in the orchestra.

Maintaining a healthy gastrointestinal barrier is essential for optimal immune function.

Of the physical barriers between your internal organs and the outside world, your gastrointestinal tract is of primary importance. The gastrointestinal tract is like an internal skin, but it has about 150 times more surface than does your outside skin. It also contains the largest number of immune cells of your whole body, constituting approximately 60% of your entire immune system.

It may be surprising that the gastrointestinal tract has more of your immune system localized within it than any other organ in your body; however, it has a very difficult role. Your gastrointestinal tract comes into contact with the largest amount and number of different molecules and organisms of any organ in your whole body. Just as an example, the average person ingests more than 25 tons of food over his or her lifetime.

And, unlike your skin or even your lungs, your gastrointestinal tract must figure out how to keep out damaging molecules and pathogenic organisms, while still letting in the nutrients and food components your body needs to survive. So, it has to be selective in its protection. The gastrointestinal mucosal layer has the unique role of keeping out damaging molecules and organisms, like harmful bacteria and viruses, while allowing in only the health-promoting nutrients, molecules and substances. In a perfect scenario, only the beneficial nutrients and phytonutrients are absorbed into the body, while non-beneficial substances and organisms never make it across this barrier and are excreted from your body.

The foods you eat can provide support for this barrier or cause damage to it. For instance, alcohol consumption is known to irritate the gastric (stomach) mucosal barrier. Some drugs, for example, the non-steriodal anti-inflammatory drugs like aspirin and ibuprofen, also can harm this barrier. Many nutrients in the World’s Healthiest Foods help to support a healthy barrier. Foods that are high in phosphatidylcholine or its precursor, choline, are particularly beneficial in supporting a healthy gastrointestinal barrier since phosphatidylcholine is one of the components of the protective mucosa that lines your intestinal tract and provides the first barrier defense. Studies have shown that diets low in choline result in low levels of phosphatidylcholine.

Maintaining healthy cells within the tissues that constitute your barriers, including your gastrointestinal tract is also vital for optimal health. Vitamin A plays an important role in supporting the cells of the skin, gastrointestinal tract and lungs – the epithelial cells – which constitute the main barriers that separate you from the external environment, plus vitamin A promotes the formation of the protective mucous in your gastrointestinal tract. Phosphatidylcholine is a component of your cell membranes, and therefore choline-rich foods also support healthy cell membranes. Essential fatty acids, such as those found in cold-water fish, and a healthy range of monounsaturated fatty acids, such as those in olive oil, can also support healthy gastrointestinal cells by promoting healthy membranes.

Finally, foods high in fiber, such as whole, fresh fruits and vegetables, promote a healthy gastrointestinal system in several ways. They are fermented by the friendly bacteria in your colon to short-chain fatty acids (SCFAs), which are used as a fuel by gastrointestinal tract cells. Studies have shown that fibers that promote SCFAs also promote a healthy gastrointestinal barrier. Fiber also promotes the removal of toxins that can adversely affect your gastrointestinal tract cells and supports healthy digestive function overall.

What nutrients support my immune system cells?

Research over the past ten years has shown that nutrition plays a major role in supporting the production and action of both the cells and the soluble factors of the immune system. Protein, antioxidants, essential fatty acids, and certain vitamins, and minerals are all key to a healthy immune system.

Protein and your immune system

Much research has shown that protein malnutrition can have a variety of untoward effects on the immune system. In fact, protein malnutrition is one of the most frequent contributing causes of AIDS (acquired immune deficiency syndrome), a condition in which the immune system functions poorly and which often results in recurrent infections and poor healing responses. In particular, a deficiency in high-quality dietary protein results in depletion of immune cells, inability of the body to make antibodies, and inhibition of the soluble factors. Animal studies have shown that the immune system can be significantly compromised with even a 25% reduction in adequate protein intake.

Protein is composed of the 20 amino acids your body needs for growth and repair, and some of these amino acids appear to be particularly important for immune functioning. For example, the amino acids called glutamine and arginine are being considered as nutrition therapy in pre-surgery patients because of their ability to stimulate the immune system. Interestingly, it is not just deficiency of these amino acids that can compromise the immune system, an imbalance in the ratios among amino acids can also affect the immune response.

Therefore, a diet that supports a healthy immune system should contain foods providing high-quality, complete protein, such as that found in eggs, fish, shellfish, and venison. Many vegetables and grains are also excellent sources of many of the immune-stimulating amino acids and, together with other protein sources, are particularly beneficial. The recipes on this web page provide many excellent menus for a meal with complete protein, such as the Baked Seafood with Asparagus, or Poached Fish with Chinese Cabbage.

The essential vitamins for healthy immune function

As discussed above, your body uses a variety of responses to maintain its defense against harmful pathogenic organisms in the environment; therefore, it may not be surprising that nearly all of the vitamins are necessary to maintain and promote some aspect of your immune function. Some vitamins have received more attention in the research literature since they are particularly important to a healthy immune system.

Much has been written about the role of vitamin C in supporting the immune system, in part because it has been promoted as an immune stimulant by the noted scientist and Nobel Prize Laureate, Linus Pauling. Vitamin C appears to support a decrease in the length of time and severity of symptoms associated with upper respiratory viral infections, promote phagocytic cell functions, and support healthy T-cell function. Vitamin C also provides antioxidant activity to support healing at sites of inflammation. An excellent source of vitamin C is citrus fruit. Many vegetables are also excellent sources of vitamin C, such as fresh parsley, raw cauliflower, mustard greens and Romaine lettuce.

Many of the B-vitamins are also very important in supporting a healthy immune system. For example, vitamin B5 (pantothenic acid) promotes the production and release of antibodies from B-cells, and deficiency of vitamin B5 results in reduced levels of circulating antibodies. Folic acid deficiency leads to a decrease in T-cells and can result in reduced effectiveness of the soluble factors as well. Vitamin B6 deficiency consistently impairs T-cell functioning and results in a decrease in blood lymphocyte counts. Deficiencies in vitamins B1(thiamin) and B2 (riboflavin) may impair normal antibody response, and low vitamin B12 appears to inhibit phagocytic cells and possibly T-cell function.

Almost all whole grains, vegetables and fruits can serve as excellent sources of at least some of these vitamins, but some vegetables are particularly beneficial since they are excellent sources of many of these immune-supporting vitamins. In particular, Romaine lettuce is an excellent source of vitamins B1, B2, C, and folate. Cooked turnip greens and boiled spinach are excellent sources of folate, vitamin B6 and vitamin C. And cooked cauliflower is an excellent source of vitamin C and folate and a very good source of vitamin B5 and B6. Raw crimini mushrooms are also an excellent source of vitamin B2 and vitamin B5. Red bell peppers are an excellent source of vitamin B6. Vitamin B12 can be obtained from protein-providing foods such as fish, shellfish, venison and calf's liver.

The fat-soluble vitamins, vitamin A, vitamin E and vitamin K are also important to overall health. Vitamin A deficiency has been shown to impair antibody function and T-cell activity. Vitamin E is an important antioxidant and supports a healthy inflammatory response. Vitamin E is also an important component of all cell membranes and promotes healthy cellular functioning overall. T-cells and B-cells from vitamin E-deficient animals show depressed responses, and tumors have been shown to grow faster in vitamin-E deficient animals. Vitamin K supports a healthy blood-clotting ability in your body, and this is necessary for seclusion of areas of infections and injury in the healing process. Cooked turnip greens and boiled mustard greens, mentioned above, are also excellent sources of vitamins E and A, as well as boiled Swiss chard. Other excellent sources of vitamin A include many vegetables such as spinach, fresh parsley and carrots. Concentrated sources of vitamin K include raw cauliflower, as well as most green vegetables such as spinach and asparagus.

Minerals that support your immune system

Zinc is one of the minerals in food that has received the most attention for its ability to support immune function. Zinc is a potent immunostimulant, and its deficiency can result in profound suppression of T-cell function. Children with severe zinc deficiencies show signs of growth retardation and susceptibility to infections. However, an excess of zinc has also shown negative effects on immune function and can inhibit the phagocytic cells (macrophages and neutrophils). So, maintaining adequate but not excessive levels of zinc is important. This is one reason food is such an excellent source of obtaining nutrition versus supplementation; food contains a balanced variety of the micronutrients whereas supplementation with individual nutrients can lead to too much of some and not enough of others. Healthy levels of zinc can be provided by including the good sources of zinc, such as boiled Swiss chard, collard greens, and both summer squash and winter squash, or the very good or excellent sources of zinc like lamb, raw crimini mushrooms and calf's liver in your diet.

Many other minerals are important in supporting immune function. Clinical research studies have shown that iron deficiency results in impaired response to antibodies, and defective phagocytic cell functioning. Copper deficiency is associated with an increase in infections and may impair development of immune cells such as T-cells and the phagocytic cells. Selenium and manganese are important for supporting healing from inflammation and may be immunostimulants. Selenium can be obtained from fish and shellfish, as well as tofu and whole grains. Excellent sources of copper are turnip greens, calf's liver and raw crimini mushrooms, and very good sources include spinach, asparagus and summer squash and boiled Swiss chard. Iron can be provided by fresh parsley, spices such as thyme or cinnamon, tofu, beans and peas, and many other vegetables such as spinach and Romaine lettuce.

Antioxidants and phytonutrients that promote healthy immune function

Reactive oxygen species, free radicals and other damaging molecules are generated at sites of infection and inflammation. Your body needs these molecules at the site of infection to help kill unhealthy cells; however, when your antioxidant systems are not functioning, or when not enough antioxidants are present in your diet, these molecules are not disarmed after they have done their jobs and can become damaging to healthy tissue as well. Many fruits and vegetables provide antioxidants and phytonutrients that help maintain healthy tissue around the sites of infection and support healing. Fruits and vegetables, especially colored foods like strawberries, cherries, carrots, and tomatoes contain many beneficial phytonutrients with antioxidant potential. More detailed information on the health benefits of phytonutrients can be obtained from the FAQ: “What is the Special Nutritional Power Found in Fruits and Vegetables”.

Are there foods that are bad for my immune system?

Your immune system is not just involved in fighting invaders like bacteria, but also becomes activated when you eat foods to which you are intolerant or allergic. Reactions to allergic foods can be quick, like the anaphylactic reaction often seen with peanut or shellfish allergies, but food allergy reactions can also be delayed and cause a number of symptoms like headaches, fatigue, muscle aches, rashes and other systemic (whole body) effects. The most common allergenic foods include peanuts and shellfish, cow’s milk, wheat, and soy; however, everyone is unique in their food intolerances and allergies.

Processed foods and foods produced with pesticides or not grown organically may also be problematic for your immune function. Toxic metals such as cadmium, lead and mercury are immunosuppressive. Some pesticides and preservatives can negatively effect the gastrointestinal lining. Food additives can also have untoward effects on the nutrient content of the food. For example, sulfites destroy thiamin-vitamin B1 in foods to which they have been added.

How do I keep a healthy “balance” in my immune system?

Your immune system is developed to be able to kill cells, such as bacteria cells or viruses; your immune cells can act against cancer cells within your body as well if it is able to tell that these cells are unhealthy to you. However, without proper control and the ability to differentiate healthy from unhealthy cells, your immune system can mistakenly kill your own healthy cells. Your inflammatory response is also developed to support healing, but when this response becomes overly active, it can become destructive. Autoimmune system diseases like rheumatoid arthritis and multiple sclerosis, susceptibility to infections, and wounds that won’t heal are some of the repercussions of immune system imbalance and dysfunction. Therefore, healthy immune and inflammatory responses must maintain a delicate balance to achieve protection without causing self-destruction.

Your body has a complex means of recognition on your cells' membranes to help your immune system. Some specific soluble factors of your immune system are also involved in turning-off your immune response. How well these responses function is defined in part by your genes; however, recent research has suggested that diet plays a much larger role in autoimmune system dysfunction than was once thought. For example, research has shown an association with low levels of vitamin D and increased risk of some autoimmune diseases, such as multiple sclerosis. Concentrated sources of vitamin D include cow's milk eggs and shellfish such as shrimp and fish such as cod.

The omega-3 fatty acids, which are produced in your body from the essential omega-3 fat – alpha-linolenic acid – have been studied for their effects on the immune system and inflammatory response. Diets low in omega-3 fatty acids are associated with chronic inflammatory conditions and autoimmune diseases. In order to achieve a more beneficial ratio of omega-3 fatty acids in your body, it is important to decrease the amount of omega-6 fatty acids in your diet, while increasing the amount of omega-3 fatty acids. This can be accomplished by reducing your consumption of meats, dairy products, and refined foods, while increasing consumption of the omega-3 rich foods such as wild-caught cold-water fish like salmon, flaxseed oil, walnuts, and leafy green vegetables.

Weight-management, nutrient-dense foods and the immune system

Research and clinical observations suggest that obesity is associated with immune dysfunction. For example, increases in the incidence of infectious illness and infection-related mortality are found in obese people. An increase in inflammation has also been seen with an increase in weight in individuals. Some studies have shown an association between high cholesterol and susceptibility to infections as well. Therefore, maintaining a healthy weight and healthy cholesterol levels may also be beneficial to your immune system's functioning.

Eating nutrient-dense whole foods is one way to provide your body with the full spectrum of nutrients it needs while keeping calorie intake to a healthy level. The World’s Healthiest Foods are analyzed for their nutrient density. Foods such as cooked turnip greens, boiled Swiss chard, raw crimini mushrooms, boiled mustard greens, boiled asparagus and Romaine lettuce provide a broad spectrum of the key micronutrients that support healthy immune function and are therefore recommended as part of an immune-enhancing diet.

What can I do to support and maintain a healthy immune system?

  • Provide support for the physical barriers in your body.
  • Support a healthy digestive process. In particular, the acidic environment provided in your stomach and the presence of digestive enzymes can destroy some bacteria and viruses that you ingest in food, and therefore, provides protection for your body.
  • Consume adequate protein and healthy fats.
  • Provide for balanced immune and inflammatory functions. Clinical studies have shown that maintaining a healthy balance between omega-3 and omega-6 fatty acids is one way to support balance in your immune and inflammation responses system. Research indicates a ratio of omega-3 to omega-6 fats of 1:4 is health-promoting.
  • Provide micronutrients and phytonutrients that support healthy immune function.
  • Decrease intake of allergens and toxins. Eating whole grains, fresh, organically grown fruits and vegetables, wild-caught fish, and meat and eggs from organically raised animals is one way to minimize the intake of toxins and unhealthy molecules that can inhibit your immune system’s ability to protect your health.
  • Maintain healthy weight and cholesterol levels. Basing your diet on nutrient-dense foods, such as those found in the World’s Healthiest Foods nutrient-dense food list, is one way to decrease calorie consumption while consuming optimal levels of micronutrients and immune-supporting phytonutrients.


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This page was updated on: 2004-11-22 13:13:25
© 2002 The George Mateljan Foundation