In the last year, we very often listen to advice and instructions about how we must strengthen our immunity and how we must eat and move so that we contribute to our immunity, which is the body's defense wall against various types of diseases. But how exactly can we positively or negatively influence our immunity with food?
How does immunity work?
The immune system is a complex network (Marshall et al.) that constantly works to protect the body against antigens associated with pathogens, including bacteria, toxins, parasites, and viruses. The immune system offers two lines of defense: innate immunity and adaptive immunity.
Innate immunity is the first line of defense and consists of physical barriers, such as skin and mucous membranes, as well as chemical and cellular defenses. The innate immune system is non-specific because it reacts in the same way to all foreign invaders.If the innate immune system is ineffective against a potential threat, the adaptive immune system takes over.
The adaptive immune system consists of specialized blood cells and proteins that target the specific cause of infection. The adaptive immune system has a “memory”, which makes a person's body immune to certain diseases after initial exposure.
A person's immune system must function well in order to stay healthy. Certain diseases, medications and lifestyle, such as smoking and excessive alcohol intake (Yamaguchi), can negatively affect immune function.
Research shows that nutrition can also significantly affect immune health.
Can nutrition affect immunity?Studies (Venter et al) suggest that a person's diet affects their immune system, as well as all other aspects of health. For example, diet can affect the microbiome, gut barrier function, inflammatory processes, and white blood cell function, all of which affect immune function.
Dietary habits and individual foods are associated with increased risk of disease, higher risk of allergy and weakened immune response.
A Western-style diet is typically high in saturated fat, ultra-processed foods, added sugar and salt, and total calories. This diet is often low in foods we associate with better health, such as vegetables, fruits and fatty fish, and is strongly associated with an increased risk of chronic disease. Research suggests that a Western-style diet causes inflammation and alters the function of the immune system, promoting the development of disease.
Conversely, a diet rich in whole foods, such as vegetables, fruits, nuts, legumes, and seafood, and low in ultra-processed foods can reduce disease risk and promote healthy immune function.
In addition, deficiencies in nutrients essential for immune function, including vitamin D, zinc, and vitamin C, can also affect the immune response. Deficiencies of certain nutrients are more common in those who eat an ultra-processed diet with little whole, nutrient-dense food.
Although it is clear that dietary choices affect overall health, including immune function, the interaction between diet and immune health is very complex. Scientists still do not agree on how the food a person consumes can help or harm immune function.
Harmful effect of unhealthy dietA Western-style diet is usually high in refined carbohydrates, added sugars, saturated fat and calories. This dietary pattern affects immune function in several ways.
Most foods in the Western diet are ultra-processed and contain high levels of added sugar, which can trigger an inflammatory response in the immune system.
For example, foods and beverages that significantly affect blood sugar levels, such as sodas, sweets, sugary cereals and pastries, increase levels of inflammatory proteins (Iddir et al.), including tumor necrosis factor-alpha (TNF-alpha), C- reactive protein (CRP) and interleukin-6 (IL-6). They also interfere with the function of protective immune cells, including neutrophils and phagocytes.
A study (Wijsman et al.) of 562 adults age 85 and older without diabetes found that subjects who had higher blood sugar levels had lower innate immune responses. They also had higher levels of CRP, a marker of inflammation. Higher blood sugar levels are associated with a weakened immune response in people with diabetes as well.
Also, a diet high in sugar and refined carbohydrates can negatively alter gut bacteria, leading to dysbiosis, which includes digestive disorders such as bloating. A healthy microbiome is essential for immune function because gut bacteria play a key role in the development and functioning of the immune system.
Experts have also linked a Western-style diet to an altered immune response due to high levels of saturated fat and added salt. Studies (Rogero et al.) show that a diet high in saturated fat can promote inflammation, modify gut bacteria and inhibit white blood cell function.
A high-salt diet has been linked to an overactive immune response, impaired regulation of inflammation in the body, and an increased risk of certain autoimmune diseases, such as rheumatoid arthritis. A Western-style diet is associated with an increased risk of developing several chronic diseases, including certain cancers, heart disease, and type 2 diabetes.
Researchers (Christ et al) attribute this to chronic low-grade inflammation and an altered immune response caused by a Western-style diet, inactive lifestyle, and exposure to toxins.
Nutrition for healthy immunity
While a diet high in ultra-processed foods, added sugar, and excess calories can lead to immune dysfunction, a diet rich in whole and nutrient-dense foods is beneficial for immune function.
The Mediterranean diet is rich in vegetables, legumes, nuts, fruits, whole grains, olive oil and other healthy foods. Research has shown that this type of diet can reduce the risk of disease, reduce markers of inflammation and beneficially modulate intestinal bacteria (Nagpal et al.).
A high-fiber diet, such as the Mediterranean diet, stimulates the production of short-chain fatty acids (SCFA), including acetate, propionate, and butyrate. SCFA are the end products of bacterial fermentation in the intestines and have a number of health benefits.
SCFAs act locally and systemically to modulate the immune response. They maintain the health and improve the immune defense function of the intestinal epithelium. This is an important part of the immune system that serves as a barrier against microorganisms. It also reduces the production of inflammatory proteins from immune cells.
A diet rich in fruits, vegetables, olive oil, nuts, seeds and oily fish contains high levels of nutrients such as vitamin A, vitamin C, zinc, vitamin D, B6, B12, copper, folate, iron and selenium. The immune system needs these nutrients for optimal functioning (Gombart et al.).
Also, a vegetarian diet reduces markers of chronic inflammation, such as CRP, fibrinogen and IL-6. This could be due in part to the array of nutritional and non-nutritive components found in fruits and vegetables that boost the immune system's response.
Food rich in healthy fats, fiber, vitamins, proteins, minerals and beneficial plant compounds helps reduce systemic inflammation, promotes a healthy balance of intestinal bacteria, reduces oxidative stress and cellular damage, and improves blood sugar and insulin sensitivity. All of these activities are crucial for healthy immune function.
In addition, dietary supplements, including vitamin D, zinc, and vitamin C, can help optimize immune function and reduce the risk of infection.
To support our immune function, we should focus on a balanced dietary pattern rich in whole foods, especially plant-based foods such as vegetables, fruits, legumes, nuts and seeds. We should avoid or limit ultra-processed foods with a high content of refined grains and added sugar, and thus directly contribute to strengthening immunity and general health through food.
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