Hippocrates said, “All disease begins in the gut.” And so it begs the question: is there a connection between gut health and the immune system?

The immune system, 70-80% of which lies behind a razor-thin, nearly invisible mucus layer next to the gut, is constantly interacting with and getting signals from the gut microbiome — a complex community of microorganisms including bacteria (over 800 different species), fungi, viruses and parasites.

Gut bacteria not only have key roles in processing nutrients and metabolites (including short-chain fatty acids, bile acids, and amino acids), but some gut bacteria also play an important immune function against pathogenic bacteria and prevent bacterial invasion by maintaining intestinal epithelium integrity.

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Research shows that if your gut gets out of balance (a condition known as “dysbiosis”), your immune system doesn’t respond effectively. Can external factors such as diet and lifestyle modulate the gut, and also the immune system?

That answer is yes, although the exact mechanisms remain unclear to scientists, and everyone’s microbiome and immune system appears to respond differently to different external factors. 

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What is the immune system?

The immune system is a complicated structure of cells, proteins and organs that work together to fight off infection and disease. It recognizes, identifies and combats any harmful cells or compounds that have entered the body through signaling pathways between the cells and tissues that comprise the entire system. Our immunity is influenced by a variety of factors, including genetics, vaccines, sleep, exercise, metabolic status, smoking status, and our diets.

The immune system consists of two subsystems: the innate immune system and the acquired immune system. Innate immunity is the first line of defense your body uses to create protective barriers that trap and destroy pathogens. Your skin, mucus layers in your nasal passages, stomach acid, and special enzymes in sweat and tears are examples of such protective barriers. The innate immune system is carried out mainly through killer cells and phagocytes (cells that engulf other cells). 

Acquired immunity, also known as adaptive immunity, is the part of your immune system that learns to recognize pathogens from infections, fungi, parasites, viruses, or vaccinations. A well-functioning adaptive immune system can distinguish between what is foreign and harmful from what isn’t, and it utilizes white blood cells called lymphocytes. There are two broad types of lymphocytes used in adaptive immune responses: B-cells and T-cells, each activated to combat different types of foreign invaders. 

What factors stress the immune system?

The immune system is constantly running to keep you healthy and maintain homeostasis. A variety of factors, some beyond your control, can influence how hard it has to work:

Antigens are substances that the body believes to be harmful, including allergens like pollen and animal dander as well as food allergens. Antigens can lead to a hyperactive immune response.

Autoimmune disorders that can be hereditary — such as type 1 diabetes, multiple sclerosis or rheumatoid arthritis — can also lead to a hyperactive immune response, destroying healthy cells.

Immunodeficiency disorders can be either genetic or acquired, and can lead to a significant reduction in the body’s immune response and resulting high susceptibility to pathogens.

Drug use — such as antibiotics, nonsteroidal anti-inflammatory drugs (NSAIDs), proton pump inhibitors (PPIs), and several other categories — have been shown to alter the gut microbiota by causing hyperactive or suppressed immune responses to diseases. 

Old age causes our bodies to become less efficient and less productive in creating what’s needed to fight off infections, and sometimes aging is associated with micronutrient deficiencies.

Environmental toxins — such as poor air quality, smoking, or excessive alcohol use — can hinder or suppress immune responses.

There are other factors that cause dysregulation, although they can at least be partially manipulated with diet and good lifestyle choices:

Obesity is associated with chronic, low-grade inflammation, which can cause too much stress on the immune system over time — and, ultimately, weaken its responses. Chronic inflammation affects the nervous system, immune system and eventually the endocrine system, and has been linked to mental health disorders, nutritional deficiencies, autoimmune diseases and energy production issues.

Chronic stress delivers a constant cortisol hormone release which suppresses the immune system’s inflammatory response and white blood cell activation. Regular exercise, a good night’s rest, and a healthy diet can decrease stress hormone levels.

Poor sleep hygiene means your body doesn’t have time to restore, including making more immune cells that fight infection.

Poor diet — especially one high in processed foods, sugars and saturated fats; and lacking in fiber and important micronutrients — can lead to gut dysbiosis, nutrient deficiency and an impaired immune system. 

Gut health and immune system

Your gut can significantly impact how the immune system functions through direct contact, cell and hormone signaling and nutrient uptake. 

As we mentioned at the outset, 70-80% of your immune cells are lying next to a nearly invisible mucus membrane layer behind your gut. These immune cells are structured like a fishing net about one millimeter thick, which allows certain things to pass through from the gut, such as digested micronutrients. This protective barrier also segregates everything that goes through your gut from what interacts with immune cells. 

The probiotic bacteria in your gut is constantly sending signals to the immune system, and when there’s something potentially harmful in your gut, the bacteria produce cells (called interferons) that interfere with pathogenic proliferation (and only sometimes signal to the immune system to act). When the gut microbiome is in dysbiosis, the mucosal barrier can be impaired, leading to an increased interaction between the immune system and potentially pathogenic bacteria — stressing the immune system, causing inflammation, oxidative stress, and insulin resistance

When the gut becomes unhealthy: impact on immunity and disease

Aberrant interactions between your microbiome and immune system, especially if you are  genetically susceptible, may contribute to the development of complex immune-mediated diseases. Among these are:

• Inflammatory bowel disease (IBD) - the most extensively studied example
• Systemic autoimmune diseases - such as Rheumatoid arthritis (RA)
• Cardiometabolic diseases - such as diabetes mellitus, obesity, atherosclerosis and non-alcoholic fatty liver disease (NAFLD)
• Cancers - most notably, colorectal cancer; but also likely metastasized melanomas, liver tumors, and epithelial tumors
• Different inflammatory skin disorders - including atopic dermatitis and psoriasis
• Chronic pulmonary diseases - including chronic obstructive pulmonary disease, asthma and cystic fibrosis
• Chronic inflammatory and cholestatic liver diseases

 Additionally, the microbiome-immunity link has been suggested to modulate other “multifactorial” diseases (e.g., neurodegenerative diseases), but these theories require further human studies. (We caution, too, that the causal effect of the microbiome on immune dysregulation in most human disorders remains to be proven.)

Modulating your gut health to boost your immune system

Constant interactions between gut microbiota and a host’s innate and adaptive immune systems are essential in maintaining intestinal homeostasis and inhibiting inflammation. Gut microbes are responsible for metabolizing food, producing critical byproducts, as well as synthesizing vitamins. Gut microbes play a direct role in producing digestive enzymes for nutrient breakdown and absorption, converting carbohydrates to short-chain fatty acids (SCFAs) — which are considered instrumental in helping to regulate the immune system, synthesizing B-complex vitamins, hormones, and neurotransmitters. In short, when your gut doesn’t have enough of the right nutrients and bacteria, the body can’t reproduce the cells it needs to fight off unwanted substances. 

Here are four steps that can help you ensure your immune system is working at its best:

Make small shifts to your snacks and meals:

Avoid highly processed foods: Highly processed foods (such as crackers, sugar-sweetened beverages, chips, deli meats and premade microwavable dinners) can cause large fluctuations in blood sugar, resulting in fatigue due to sugar crashing. In addition, food processing negatively impacts nutrition and can lead to long-term changes in dietary behavior which can lead to increased gut inflammation. In short, the less processed the food, the better. Put another way, stick as much as possible to fresh, whole foods.

Eat lots of fiber, especially prebiotics — and within that group, especially “microbiota accessible carbohydrates” (or MACs) — which have been shown to promote gut diversity, resulting in increased quantities of short-chain fatty acids (SFCAs), metabolites which play a vital role in the maintenance of gut, metabolic, cardiovascular, immune, and cognitive health. One particularly notable benefit of certain key fibers is their ability to increase the relative proportion of “good bacteria (such as Bifidobacteria) over “bad,” which has been associated with improved immunity, among other health benefits. Foods that boost immune system include: vegetables (such as kale, collards, broccoli, Brussels sprouts); fruits (such as bananas, pears, apples, oranges, grapefruits, berries); beans, lentils and legumes; whole grains; and seeds (such as chia, pumpkin or sunflower).

Consume multi-strain probiotics (e.g., Bifidobacterium and Lactobacillus, normally found in fermented foods such as yogurt and kefir): Especially when combined with prebiotics, (i.e., in a synbiotic blend — see next section), probiotics can contribute to the healthy composition of gut microbiota while providing relief from various gastrointestinal (GI) ailments and other disorders. 

Up your consumption of PUFAs: Omega-3 and omega-6 polyunsaturated fatty acids (PUFAs) are not only associated with heart health benefits, but also have important immune-regulatory functions. Omega-3s play an anti-inflammatory role, ensuring that excessive or prolonged immune responses do not occur. The PUFAs found in fatty fish (such as salmon, trout, anchovies, sardines, and herring) contain the two most important immune-boosting omega-3 fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). DHA appears to be the more powerful of the two on markers of inflammation in the body, yet EPA helps maintain a balance between pro-inflammatory and anti-inflammatory proteins. Nuts and seeds are a good source of α-linolenic acid (ALA) omega-3s,  and a quantity of DHA can be synthesized from the ALA. Omega-6s, mainly linoleic acid (LA), are contained in seed oils (such as sunflower, safflower, soy, canola, sesame, and corn oils). LA and its byproducts play a critical role in immune responses like redness, swelling, heat, and pain. While both play a role in immune function, studies show that a higher omega-6:omega-3 ratio can result in lower immune functioning, so it’s best to consume more omega-3s from fish, primarily; nuts and seeds secondarily; and less omega-6s from seed oils. 

• Eat foods rich in other important micronutrients: Vitamins, minerals and polyphenols are also essential for strong immunity.
• Certain vitamins have been shown to beneficially modulate the gut microbiome by increasing the abundance of presumed commensals (vitamins A, B2, D, E, and beta-carotene), increasing or maintaining microbial diversity (vitamins A, B2, B3, C, K) and richness (vitamin D), increasing short-chain fatty acid production (vitamin C), or increasing the abundance of short-chain fatty acid producers (vitamins B2, E). Others, such as vitamins A and D, modulate the gut immune response or barrier function, thus, indirectly influencing gastrointestinal health or the microbiome.
  
  
• Polyphenols and other phytonutrients have been shown to reduce oxidative stress, support the liver to promote efficient biotransformation and detoxification, and modulate gut microecology — processes which help to boost overall immune system function. Quite a number of them have been linked to reductions in risk of major chronic diseases. (However, the effects of interplay between polyphenols and specific gut microbiota functions remain largely uncharacterized.)
  
  
• Fortunately, many of the same foods listed previously (e.g., fruits, vegetables) that represent good sources of prebiotic fiber also tend to be rich in vitamins, minerals and various polyphenols. We provide more detail on optimal food sources in: The best foods for a strong immune system.

2. Avoid smoking and excessive alcohol use, which can depress your immune system’s responses.

3. Avoid unnecessary medications or medication overload. Scientists have established that antibiotics can lead to gut dysbiosis, killing both pathogenic bacteria and good gut bacteria — although the importance of factors such as drug type, dosage, route of ingestion as well as stress and environment are still being studied. Research has also shown that use of drugs like proton pump inhibitors (PPIs) can weaken the immune system because of their effect on the gastrointestinal microbiome. Speak to your medical professional about how your medications might be affecting your gut. 

4. Make sure you exercise. Exercise has numerous health benefits, including in the gut. For example, exercise can improve lipid profiles by increasing the amount of high-density lipoprotein (the “good cholesterol”). In addition, exercise improves glucose regulation and can improve mental health.

5. Get enough sleep and find ways to de-stress. When your body doesn’t get enough sleep, it can negatively affect your mood and hormone levels, including your hunger hormones and cortisol stress hormones. It turns out that there is a robust connection between sleep and metabolic health, and too little sleep can negatively affect insulin resistance, which is a key driver of diabetes.

Eden’s synbiotic for immune health

To supplement your diet, Eden’s Synbiotic Supplement was developed not just to improve digestive functioning and comfort (i.e., reduce symptoms of gastrointestinal distress), but also to improve markers of metabolic, cardiovascular and immune health. This synbiotic blend contains five carefully selected prebiotics, four strains of probiotics, and five key polyphenols.

Eden’s Pilot Participation Study demonstrated a 222% increase in Bifidobacteria, the “good bacteria” that, as we explained previously, is strongly associated with improved immunity (as well as digestion). 

While the importance of Eden’s should really only be measured by how the blend, overall, benefits human health, it’s important to note that where immunity is concerned, these Eden’s ingredients have particularly strong associations with advantageous immune responses:

• A prebiotic fiber resistant potato starch (Eden’s is a formulation called Solnul) bypasses digestive enzymes so that it reaches the colon intact, where it feeds beneficial flora. In human clinical research, resistant potato starch has demonstrated an increase in the total amounts of both a “good” bacteria (Bifidobacterium) and total SCFAs, results associated not only with improvements in digestion, reduced symptoms of irritable bowel syndrome (IBS), and better glucose management, but also with enhanced immune system function.
  
  
• Another prebiotic fiber, beta glucan (Eden’s is sourced from barley) has been widely studied for its beneficial impact on the immune system, particularly for "modulating the inflammatory and antimicrobial activity of neutrophils and macrophages," as well as other innate immune cells such as dendritic cells, granulocytes, and natural killer cells.  One way that beta glucan helps the immune system is by training innate immune cells to have a more effective response against harmful threats in the body, such as a pathogen invasion.
  
  
• The probiotic, Lactobacillus rhamnosus GG (often referred to as LGG) is one of the most common naturally-occurring beneficial gut bacteria. This strain is resistant to bile and acid, which allows it to proliferate in the gut microbiome. Both in vitro and human trials have elucidated strong evidence to support LGG’s effect not only in alleviating GI upset, but also for stimulating the immune response.
  
  
• A similar probiotic, Lactobacillus paracasei (LPC-37), is a "good" bacterium that helps to strengthen the immune system and the intestinal barrier, while also improving nutrient absorption.

Key takeaways

What's the connection between gut health and the immune system? Gut health has a significant impact on the immune system because of its proximity, metabolic role and signaling pathways. The foods we eat and our behaviors affect the diversity and composition of the gut bacteria, which can support or weaken the immune system. A well-balanced, varied diet focusing on gut-healthy foods can help maintain or improve your gut microbiome, with wide-ranging health impacts — including on your immunity. Diet is not the only factor involved, but its impact appears significant, even though much more research remains to be done to understand mechanisms, causality, and the relative merits of various nutritional and other therapies. Regular exercise, good sleep hygiene and finding ways to release stress are also important to immune health.