Choosing the Best Immunity-Boosting Foods

Nutrition plays a major role in determining the health of your immune system.

What are the best immune boosting foods? Your immune system is complex and unique to you. Many factors affect it, including genetics, medical conditions, and lifestyle factors (smoking, alcohol, stress, sleep). Nutrition also plays a major role in immune function, but no single food or nutrient will prevent illness. To be healthy, your best diet should include foods from five dietary categories that contain the micronutrients deemed most important for the growth and function of your immune cells and processes: high-fiber prebiotic foods (such as vegetables, fruits, beans and legumes, whole grains), vitamin- and mineral-rich foods, key proteins and healthy fats (such as Omega-3s), antioxidant-rich foods (polyphenols) and sufficient hydration. 

What is the immune system?

Your immune system is a large network of organs, tissues, white blood cells, proteins (antibodies) and other chemicals. This system works together to protect you from foreign invaders (bacteria, viruses, parasites, and fungi), known as pathogens, that cause infection, illness and disease. Typically, when your immune system comes into contact with a pathogen, it triggers an immune response, which then releases antibodies that attach to the pathogens and dismantle them. When your immune system doesn’t succeed in dismantling a pathogen, a medical problem results — like an infection. 

Sometimes your immune system mounts an attack when there is no pathogen, or doesn’t stop an attack after the pathogen has been killed. Autoimmune diseases and allergic reactions can result from such an overreacting or malfunctioning immune system. You may have heard that during the current COVID-19 (also known as SARS-CoV-2) pandemic, this same sort of immune system overreaction has been a serious complication of some people sickened with this virus, especially unvaccinated individuals with comorbidities (including diabetes, hypertension, heart conditions, and chronic lung, kidney or liver diseases). Such patients experienced what is called a “cytokine storm,” which occurs when the host immune response to the SARS-CoV-2 virus is hyperactive — resulting in an excessive inflammatory reaction. Such an acute reaction unfortunately correlates directly with lung injury, multi-organ failure, and unfavorable prognosis of severe COVID-19, as detailed in this 2020 review paper.

Your immune system and “the two sides” of inflammation 

The uncommon but still possible cytokine storms in some patients with severe COVID-19 serves as a telling example of how complex the relationship is between your immune system and what scientists refer to, generally, as “inflammation” — a set of pathways that seemingly come from the immune system as well as lead into it. As one research team aptly stated, “the immune system is a complex organization, which is often neither pro- nor anti-inflammatory per se.”

What that means, put simply, is that inflammation can be either a good thing or a very bad thing for the body. As we noted in our report, Blood Sugar, Diabetes and Inflammation, an inflammatory response often represents a defense mechanism that helps your body heal after it’s been attacked by, say, an infection or an injury. Acute inflammation rallies the body’s defenses (aka your immune system) to get to work so you feel better faster, whether that means protecting a cut from infection or fighting off a virus. In these need-help-now situations, you’ll be glad acute inflammation is triggered to aid in your body’s healing process. Yes, it might come with symptoms like redness, swelling, or fever, but those are actually signs that your body is flooding the hurt area with immune reinforcements to bring you back to pain-free normal. 

Inflammation crosses into the danger zone when it can’t shut itself off … and becomes chronic. When the body is in a perpetual state of low-grade inflammation, your immune system ends up damaging, instead of healing, your systems — and a host of health harms can result. Excess weight or obesity, high blood glucose levels, genetic bad luck or any of dozens of other factors (and possibly a combination of them) can trigger chronic inflammation and lead to such diseases as type 2 diabetes, cardiovascular diseases, fatty liver disease, inflammatory bowel disease and certain cancers.

What factors affect inflammation and the health of your immune system?

All of the following factors can affect your inflammatory pathways and the health of your immune system:

  • Genetics
  • Nutrition/diet
  • Weight
  • Exercise
  • Smoking
  • Alcohol or drug use (including certain prescription medications)
  • Stress
  • Sleep health
  • Body hygiene (hand-washing, mask-wearing)

You can probably guess which of the above-listed factors are considered beneficial vs. harmful to your immune system. Clearly, genetics and nutrition are major drivers, and can go either way: helpful or harmful. Maintaining a healthy weight, exercising, managing stress levels, practicing good hygiene and sleeping well are all beneficial to your immune health, whereas smoking and consuming too much alcohol are harmful. 

Nutrition’s impact upon your gut microbiome, inflammation and immunity

As we detailed in our report, Why The Gut Microbiome Is Key To Your Health, researchers have concluded that a healthy gut microbiome — that array of microorganisms, also called microbes, in your gastrointestinal (GI) tract that include bacteria, fungi, viruses and parasites — helps keep your immune system healthy. An intact gut microbiome is critical for training your immune system so it reacts beneficially to harmless microbes or food particles while fighting off pathogens. Gut microbiome composition can also promote or control gut inflammation. (Generally speaking, the less inflammation the better, from a disease perspective.) 

What you eat makes a difference, because diet modulates the gut microbiome — which in turn can impact the immune system. Conversely, gut microbial changes have been implicated in low-grade inflammation, which is typically associated with an immunocompromised state of health. “Metabolic inflammation” is exactly what it sounds like: chronic inflammation that takes aim at your metabolism. Some researchers call it “metainflammation.” This is often triggered by excess weight or obesity or other conditions that cause insulin resistance, which can lead to hyperglycemia (high blood glucose levels). 

But exactly why some people who, for example, are obese and eat certain foods and then become metabolically unhealthy (e.g., develop type 2 diabetes), while others with the same profile and diet do not, is still being researched by scientists. Researchers have observed that both functions, the gut microbiota and the intestinal immune system, are disturbed in metabolic diseases; however, they aren’t clear which disturbance comes first. (Future scientific/medical research will need to better identify and describe the underlying metabolic and inflammatory pathways, which is a challenge when you consider that many inflammatory mediators have dual roles and some serve important physiological functions other than purely inflammation.)

The challenge of choosing the best immune boosting foods

Given that scientists are still in the early stages of understanding the complex interplay of the immune system, gut microbiome, and inflammatory pathways, physicians and nutritionists alike are challenged when it comes to recommending preventative measures (such as “what’s the best diet”) to help avoid sub-optimal immune health and the disorders that can ensue from it. What leading medical organizations do believe is that the best way to stay healthy is to maintain a well-functioning immune system in order to prevent immunodeficiencies. That is, a “good diet” can’t really “boost” an already unhealthy immune system. So, to stay healthy, these are the top food groups that should make up the heart of your meal-planning selections:

1. Fill up on prebiotics

  • Vegetables (such as kale, collards, broccoli, Brussels sprouts)
  • Fruits (such as bananas, pears, apples, oranges, grapefruits, berries)
  • Beans, lentils and legumes
  • Whole grains
  • Seeds (such as chia, pumpkin or sunflower)

These are examples of prebiotics, fibrous foods (non-digestible carbohydrates) that can assist in maintaining the higher microbial gene richness that scientists associate with lower inflammation. (Learn more: What Is Fiber?). 

The prebiotic fibers in these foods are not digestible by mammals, are fermented (digested) by microbes and promote the production of short-chain fatty acids (SCFAs) and other beneficial metabolites from your resident gut bacteria — which in turn help you maintain a strong intestinal barrier, induce the production of protective mucus, and regulate glucose, lipid and the immune systems. By contrast, low fiber diets — such as the common Western diet — are associated with microbiome dysbiosis and increased inflammation. SFCAs also appear to increase regulatory T cells, which help maintain immune system homeostasis and prevent your immune system from reacting to things it shouldn’t. In addition, SFCAs appear to regulate signaling by molecules called G-protein coupled receptors, which help regulate metabolism, inflammation, and disease.

Fibrous foods can also help your body absorb nutrients (such as calcium). Furthermore, because your body doesn’t break fiber down into glucose, fibrous foods are carbohydrates that mitigate sharp spikes up in your blood sugar levels. High blood glucose can trigger inflammation, which in turn contributes to even higher blood glucose levels… a vicious cycle that can lead to type 2 diabetes. (Learn more: Blood Sugar, Diabetes and Inflammation).

Another benefit: fibrous prebiotic foods are typically nutrient-dense and can help you feel full longer than other carbohydrates (such as simple sugars found in processed foods like cakes, candies, soda, fruit juice, ketchup, sauces, and ice cream), which can assist you in your weight management plans. And a healthy weight is associated with immune health.

Learn more: Confused About Carbohydrates?

2. Fill up on vitamin- and mineral-rich foods

Fortunately, many of the fiber-rich prebiotic carbs we cited in #1 are the same foods that very often represent the best sources of immune-important vitamins and minerals. As we discussed in our recent Vitamins and Minerals report, most healthy individuals don’t need any nutritional supplements if they eat a variety of such prebiotic foods, plus low-fat dairy products, lean meats and fish. (In fact, our report detailed the toxicities that can result from overdosing on certain vitamins and minerals in supplement form, especially the fat-soluble vitamins A, E and K.) But some of us might benefit from Vitamin D, B12, magnesium or iron in supplement form if we are found to be deficient in one or more of those nutrients. 

From an immune health standpoint, the most important nutrients are:

  • Vitamin A is important for visual health and immunity. You can usually get enough from such natural sources as carrots, sweet potato, spinach, broccoli and red bell peppers; and to a lesser extent from meat, poultry, fish and dairy products.
  • B vitamins (niacin, B6, B9, B12) are important for the development and function of cells in your body, as well as immune function. 
    • Niacin is plentiful in most animal foods and some nuts and legumes
    • B6 is plentiful in animal foods, starchy vegetables and fruits
    • B9 is plentiful in many vegetables, fruits, nuts and beans
    • B12 is plentiful in foods of animal origin, including fish, meat, poultry, eggs, and dairy products; as well as in fortified breakfast cereals. (However, you can also get vitamin B12 deficiency if you follow a vegan diet of no animal products such as meat, milk, cheese, and eggs; or you are a vegetarian who doesn’t eat enough eggs or dairy products to meet your vitamin B12 needs. In both of those cases, you can add fortified foods to your diet or take supplements to meet this need.)  
  • Vitamin C can shorten the duration of certain viral illnesses; however, research hasn’t proven it helps you avoid getting sick. Citrus fruits, strawberries, red bell pepper and kiwi, spinach, and broccoli are all rich in vitamin C.
  • Vitamin D: Evidence on D’s immune-boosting properties is mixed, but some studies show certain benefits. In a sunny climate, you get enough D from being outdoors 10-15 minutes/day. (If you don’t get sun for a lengthy period of days, a supplement may be beneficial.) Dietary sources include eggs, tuna, salmon and fortified milk or orange juice, fortified cereal.
  • Vitamin E can play a dual role in boosting the body’s immune response and acting as an antioxidant (see next section) in the body, helping to protect cells from the damage caused by free radicals. You can usually get plenty from dietary sources such as vegetable oils, nuts, seeds, cheese, spinach and avocado.
  • Iron is critical for immune cell function. Dietary sources include red meat, beans, nuts and fortified breakfast cereals.
  • Zinc is often touted as an immunity-booster, but there’s not enough evidence to support taking extra zinc to keep sickness at bay — unless you are unable to get enough of it from food sources. Meeting daily zinc requirements is important for maintaining a healthy immune system, but exceeding these requirements can be toxic. In 2009, the Food and Drug Administration warned consumers to stay away from zinc nasal sprays after studies found they could damage the sense of smell. Zinc can also interfere with the effectiveness of antibiotics or negatively interact with some blood pressure and rheumatoid arthritis medications, so check with your doctor before adding it to your diet. Zinc-rich foods include beans and lentils, chickpeas, seeds, nuts, lean meat, poultry and seafood (raw oysters, especially) and fortified breakfast cereals.
  • Selenium: If you’re low on this mineral, you may be more likely to get a more severe flu, but selenium is plentiful in many whole grains and dairy products, including milk and yogurt, meats, chicken, fish, shellfish, eggs and mushrooms.

3. Incorporate antioxidant-rich foods (polyphenols) into your diet

  • Fruits: berries, currants, grapes, cherries, stone fruits, apples, pears, pomegranates, and some citrus fruits
  • Vegetables: artichokes, carrots, potatoes, onions, spinach, shallots, broccoli, and asparagus
  • Legumes: black beans, soybeans and soy products, and white beans
  • Nuts and seeds: almonds, hazelnuts, pecans, walnuts, and flax seeds
  • Grains: oats, rye, and whole wheat
  • Herbs and spices: basil, marjoram, parsley, peppermint, and spearmint (all dried); cinnamon, cloves, cumin, caraway, rosemary, sage, thyme, and star anise
  • Others: black and green tea, coffee, dark chocolate, red wine, vinegar, ginger, and olives (including olive oil)

Once again, many of the foods in this third category, antioxidant-rich foods, are the same as some of those contained in category #1 (prebiotic, high-fiber carbohydrates) and/or category #2 (vitamin- and mineral-rich foods).

As we detailed in our report, What Are Polyphenols?, antioxidant compounds have anti-inflammatory properties and therefore have the potential to reduce the risk for any disease characterized by increased inflammation. Studies link polyphenols to lower blood pressure, reduced bad cholesterol, and a resulting reduced risk of death from heart disease. Other ways polyphenols might help support a healthy body include: supporting healthy digestion, supporting brain function, and reducing the risk of type 2 diabetes

4. Eat enough of the best proteins and the healthiest fats (including Omega-3s)

Specific amino acids found in protein are essential for T-cell function, which are cells that protect the body against pathogens.

The better sources of protein are those lower in saturated fats:

  • Lean meats
  • Fish and seafood
  • Eggs
  • Beans
  • Nuts
  • Seeds 

As we reported in Dietary Fats: Which Are Healthy, Which Are Not?, when you are deficient in Omega-3s — which are essential, unsaturated fatty acids, you are at greater risk of inflammation leading to atherosclerosis, obesity and diabetes. One research paper aptly listed the entire set of health benefits associated with Omega-3s:

“Omega-3 fatty acids are more effective for raising energy levels, stamina and performance, improving concentration, learning, calmness, behavior and IQ, lowering cardiovascular risk factors, inhibiting cancer growth and metastasis, increasing insulin sensitivity, speeding the healing of wounds due to accidental injury, physical exertion and surgery, decreasing inflammation and joint pain, dampening the symptoms of autoimmune diseases, improving bone mineral metabolism, improving weight management and increasing fat burning and decreasing fat production.”

Natural dietary sources of Omega-3s include: 

  • Fatty fish (think salmon or mackerel)
  • Nuts
  • Seeds
  • Oils
  • Vegetables (such as Brussel’s sprouts)
  • Herbs (such as basil)

5. Stay hydrated

As we detailed in our report, Dehydration And Diabetes, water intake has been inversely associated with the risk of developing hyperglycemia (high blood sugar). In other words, the more water study subjects consumed, the lower their risk of extreme glucose spikes.

Relative to immune health, hydration is clearly beneficial. Hydration — together with other  properties that may help fight inflammation and get mucus flowing — may be a factor in the healing benefits that some preliminary research has found with consumption of chicken soup.

6. Fermented foods and probiotics are still being studied

Probiotic bacteria are found in yogurt and other fermented dairy products, fermented foods and beverages (kimchi, kefir, kombucha, and others) and in supplements (powder or pills).

While they have shown efficacy in treating certain gut conditions such as antibiotic-associated diarrhea, inflammatory bowel disease (IBD), constipation, and other diseases (see What Are Probiotics?), their place in a diet aimed at maintaining strong immunity in healthy individuals remains under study. A 17-week randomized, prospective study published in 2021, which looked at both plant-based high-fiber diets and diets rich in fermented foods, concluded that a high-fermented-food diet “may be valuable in countering the decreased microbiome diversity and increased inflammation pervasive in industrialized society” and that “coupling dietary interventions to deep and longitudinal immune and microbiome profiling can provide individualized and population-wide insight.” However, it remains to be seen whether fermented foods promote absolute improvements in clinically relevant outcomes such as fasting glucose levels or a reduction in human metainflammation.

Key Takeaways

This report identifies the key dietary categories that we should all consider when we’re meal planning: prebiotic fiber-rich carbohydrates, vitamin- and mineral-rich foods, antioxidant-rich polyphenol foods, lean proteins, healthy fats (especially Omega-3s) and plenty of fluids (water, in particular). Fermented foods may also provide immunity benefits, although the research is still preliminary. The recipe for maintaining the health of your immune system really isn’t that complex: Fill up your plate with a large portion of vegetables (especially the leafy green ones) and whole fruits (mixing berries and citrus fruits), add smaller sources of healthy fats and lean proteins (especially Omega-3-rich fish, lean chicken, beef, eggs, nuts or whole grains), and try to avoid foods that have been refined or processed (from white rice to bacon to candy to soda).

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