A healthy body begins with a strong immune system. Our immune system protects us from threats originating both outside the body—such as viruses and bacteria—and from internal challenges as well. Because more than half of our immune system is closely connected to the gastrointestinal tract, it’s no surprise that what we eat plays a major role in overall health. The foods we choose influence not only our physical well-being but also our mental health. Research shows that regularly consuming a plant-rich diet, especially one abundant in leafy greens, is associated with less inflammation, an improved mood and better mental health.
The foods we eat can either place stress on the immune system by promoting inflammation or support it by helping the body defend against illness. In one study examining vaccine response, individuals who consumed five or more servings of fruits and vegetables daily for several months before vaccination demonstrated an 82% stronger antibody response compared with a control group—a powerful example of how nutrition directly influences immune function.
When we start to feel sick, many of us try to “boost” our immune system by quickly adding supplements or vitamins. However, the strongest defense is built long before illness appears. Rather than reacting only when symptoms arise, the goal should be to consistently support and balance the body’s natural defense systems by providing the nutrients and lifestyle habits they need to function optimally every day. So how do we do that?
Identify Immune-Reactive Foods
A helpful first step in supporting your immune system is identifying foods that may not agree with your body. While heavily processed foods and excess sugar are obvious triggers for many people, some foods commonly considered “healthy” can also cause issues for certain individuals. Because each body is unique, the optimal diet is unique as well. One person may react poorly to dairy, while another may find that tomatoes or another food cause discomfort.
Signs of food sensitivities can vary and may include bloating, digestive discomfort, joint pain, mood changes, low energy, headaches, or even skin and vision concerns. Paying attention to how you feel is key. If you notice symptoms, reflect on what you’ve eaten in the previous 12–24 hours. Keeping a simple food and symptom journal can help reveal patterns over time.
For many people, removing or reducing problematic foods can significantly improve how they feel and may help support a stronger, more balanced immune system. Some individuals find it helpful to have guidance during this process. Working with a coach or nutrition professional can provide education, structure, and support while identifying trigger foods and developing a sustainable plan for moving forward. If this is something that would benefit you, contact me to work together!
Add Immune-Stabilizing Foods
Immune-supportive foods are those that help proactively strengthen and stabilize the immune system. They provide essential nutrients the body relies on to function optimally, and deficiencies in any one of these nutrients can weaken our natural defenses. Plant-based foods are especially powerful because many of their pigments, aromas, and natural compounds are absorbed into the bloodstream and interact with our organs, tissues, and cells throughout the body.
Garlic is a great example. The familiar “garlic breath” doesn’t come only from garlic remaining in the mouth—it also results from beneficial compounds that are absorbed into the bloodstream and later released through the lungs. Because of this process, garlic is believed to help support respiratory health by assisting the body in clearing bacteria.
What we eat influences every system in the body, including immune function. Below are several foods to consider incorporating into your routine to help optimize immune health. While animal-based foods can provide some of these nutrients, this article focuses primarily on a plant-forward approach.
Vitamin A – This is in a lot of leafy greens. Orange vegetables also help to improve your Vitamin A levels. Some delicious ones that you may want to try are winter squash, sweet potatoes, and bell peppers.
B Vitamins – These can be found in pine nuts, Jerusalem artichokes, asparagus, nutritional yeast, watermelon, whole grains, acorn squash, sunflower seeds, sesame seeds, garlic, peas, and most beans. If you do not eat meat, make sure that you are getting Vitamin B12. This can come from some fortified plant-based milk products or you may want to consider taking a supplement.
Vitamins C – Blueberries offer more powerful disease-fighting antioxidants than any other fruit or vegetable. Other powerful foods include broccoli, spinach, citrus, pumpkin, tomatoes, garlic, pomegranates, cranberries, bell peppers, and strawberries. Don’t forget that broccoli and other cruciferous vegetables need to be cut and left to sit before you eat them (click here to learn why). Here’s a random fact for you: Aside from humans, guinea pigs are the only other mammal that does not make its own Vitamin C. We, along with guinea pigs, have to get it from our food!
Vitamin E – Green leafy vegetables, blueberries, seeds, nuts (especially walnuts), soy, and pumpkin are great ways get your Vitamin E.
Vitamin D – Mushrooms—along with fortified cereals and plant-based or dairy milks—are excellent sources of vitamin D. Here’s an interesting tip: if you place shiitake mushrooms upside down in direct sunlight, their vitamin D content increases dramatically. Allowing them to fully dry helps preserve this boost, so they can be stored and used later as needed. One study found that sun exposure raised vitamin D levels in mushrooms from about 100 IU to nearly 46,000 IU.
In addition to dietary sources, don’t forget the importance of sunlight itself. Spending 10–30 minutes outdoors in midday sun several times per week can help support and maintain healthy vitamin D levels.
Probiotics – Not only do they stimulate the immune system, but they also help to lower the risk for cancer by decreasing inflammation and reducing the growth of cancer-causing microflora. Plant-based yogurt and kefir are great sources of probiotics. If you choose, this is one of the few nutrients that can be effectively obtained from a supplement. Studies have shown that people who take probiotic supplements appear to have fewer colds and sick days.
“The first study [on probiotics and immunity] demonstrated that white blood cells extracted from subjects on a probiotic regimen for a few weeks [had] a significantly enhanced ability to engulf and destroy potential invaders. This effect lasted for at least three weeks after the probiotics were discontinued.”
– Dr. Greger, How Not To Die
Amino Acids – L-lysine (beans, most fruits and vegetables) and L-arginine (Coconut, oats, nuts, whole wheat, peanuts, soybeans and wheat germ) are also key for a healthy immune system.
Zinc – Some examples of plant-based food containing zinc are beans, nuts, whole grains, shitake mushrooms, tofu, oatmeal, and fortified breakfast cereals.
Iron – Iron is found in foods such as whole grains, legumes, nuts, seeds, and leafy green vegetables. For optimal absorption and bioavailability, plant-based iron is best consumed alongside a source of vitamin C, such as citrus fruits, peppers, or tomatoes. While adequate iron intake is essential for health, too much iron can be harmful, making balance especially important.
Research from Harvard and the National Institutes of Health has suggested that heme iron—the form found in animal products—has been associated with higher risks of certain cancers and earlier mortality, whereas non-heme iron from plant foods has not shown the same associations. This difference may be related to the body’s natural ability to regulate iron absorption. When iron levels are sufficient, the body is much more effective—up to five times more efficient—at limiting the absorption of plant-based iron compared with iron from animal sources.
Copper – Look to wholegrain foods, quinoa, nuts, seeds and beans for your sources of copper.
Mushrooms – These need a special mention when it comes to our immune system. One study found that eating mushrooms boosted the levels of IgA (antibodies that help to prevent viruses from entering our body) by 50%. These levels remained high for about a week, so try making mushrooms a regular part of your diet,
Spices – High in phytonutrients, spices help to boost our immune systems. Phytonutrients are what help protect plants from germs, fungi, bugs, and other threats. In similar ways, they provide protection to our body. Some examples are turmeric, which provides us with the phytonutrient curcumin, garlic gives us allicin, and hot peppers deliver capsaicin. There are many other powerful spice options, so add them wherever you can!
Omega-3s – Most people have heard that salmon is high in Omega 3s, but what are the plant-based sources? This is where nuts and seeds come in. Flaxseed, chia seeds, and walnuts are all high in Omega 3s and should be a regular part of any diet.
Water – Don’t forget to drink plenty of fluids! Water, tea, and soup broth hydrate your immune system so it can do its job. The fluids protect the mucous membranes by making sure that they are in good shape and able to kick the germs out.
At first, this may seem like a lot to think about. Fortunately, as you may have noticed, many of the foods overlap across nutrients. Also, some find it helpful to keep a checklist throughout the day. This helps you to keep track of what is left and where to place your focus as the day goes on. You may also find that over a period of a few days, there are one or two nutrients that you are consistently missing, and can then load up on those foods the next time that you shop.
The immune system is a big topic. So much so in fact that there is more to come. Click here for part 2 on ways to support your immune system. This will focus more on the power of herbs and other tips for a healthy immune system.