The impact of diet on boosting immune function

By Priyanjana Pramanik, MSc.Nov 27 2023Reviewed by Benedette Cuffari, M.Sc.

In a recent review in Food Science & Nutrition, researchers summarize current medical knowledge regarding the role of fruits, vegetables, spices, animal products, and other foods in strengthening the immune system.

Study: Common foods for boosting human immunity: A review. Image Credit: Tatjana Baibakova / Shutterstock.com 

Background

The human immune system protects the body from pathogenic invasion. Humans are born with innate immunity, with cells such as macrophages and neutrophils, while other forms of immunity, such as some types of white blood cells or lymphocyte cells, are acquired through exposure to pathogens.

A healthy diet is critical for maintaining and improving immunity. Immune cells require sufficient energy to function, while micro- and macronutrients maintain immune responses.

While the immunological function of specific nutrients such as vitamins, minerals, and fibers has been reviewed in previous studies, the immune benefits of specific food items have not been explored.

Immune system and nutrition

In humans, the immune response is primarily derived from active immunity, in which antibodies are produced within the body. In addition to immune cells, other components of the immune system include physical barriers such as the skin, physiological barriers such as saliva and stomach acid, and complement proteins.

Antibodies or immunoglobulins, which are produced due to exposure to pathogens, include immunoglobulin A (IgA), IgD, IgE, IgG, and IgM. T- and B-lymphocytes, such as suppressor T-cells, killer T-cells, and helper T-cells, are instrumental in identifying, attacking, and eliminating pathogens. Organs like the spleen filter infections and abnormal cells in the blood, whereas glands can trap germs and other foreign materials.

Making healthy lifestyle choices such as consuming a nutritious diet, following a regular sleep schedule, minimizing stress, and avoiding unhealthy habits like smoking can strengthen immunity and reduce the likelihood of suffering from certain health conditions.

In addition to plant- and animal-based foods, water has an important role in boosting immunity. Staying hydrated keeps mucous membranes moist, cells oxygenated, and various systems functioning.

Toxins are carried to the kidneys and then the urinary tract before being expelled from the body, whereas dehydration could lead to their accumulation and subsequent illness. Drinking sufficient quantities of water can also prevent urinary tract infections by preventing the formation of kidney stones.

Inadequate consumption of nutrients can weaken the development of the immune system and render the body more vulnerable to allergies, infections, and chronic inflammation. This underlines the significance of adequate nutrition in the optimal functioning of the immune system. 

Foods and nutrients that boost immunity

Citrus fruits like oranges and lemons are rich in vitamin C, which promotes the formation of lymphocytes, strengthens the body’s epithelial barriers, and functions as an antioxidant by reacting with free radicals, which can damage the immune system. Other beneficial compounds found in citrus fruits include selenium, dietary fibers, folic acid, and flavonoids, which are antioxidative and anti-inflammatory agents.

Papayas contain folic acid, retinol, riboflavin, thiamine, niacin, potassium, iron, fiber, and calcium. Carotenoids such as beta-carotene can be converted to vitamin A and strengthen the immune response, while retinoic acid promotes lymphocyte growth.

Kiwis also contain vitamin C, vitamin K, potassium, carotenoids, fibers, and antioxidants. Pomegranates have antiviral properties and can suppress germs such as Listeria, Clostridium, and Salmonella, while promoting healthy bacteria such as Lactobacillus and Bifidobacterium.

Indian gooseberries contain a powerful antioxidant called ellagic acid, while almonds are rich in vitamin E. Broccoli is rich in fiber and a number of antioxidants, as well as vitamins A, C, and E, phytochemicals such as polyphenols, minerals, and vitamins.

Ginger, in addition to being a promising immunomodulator, also enhances digestion and improves appetite, which can also be beneficial for the immune system. Garlic, turmeric, onion, mushrooms, and tea are also beneficial foods to include in regular diets for a healthier immune system.

The role of animal-sourced foods (ASF)

An important characteristic of ASF is that they contain easily digestible and high-quality proteins, as well as essential amino acids and micronutrients. Prolactin, which is a hormone found in milk, promotes lymphocyte and thymocyte movement. Milk also contains immunoglobulins and whey proteins, which stimulate the synthesis of antibodies.

Yogurt is similar in composition to milk; however, calcium can be absorbed more easily from yogurt than milk. In addition to proteins, vitamins, and minerals, eggs contain choline, which breaks down an amino acid called homocysteine, which has been linked to cardiovascular disease.

Conclusions

While medicine has a critical role to play in healing from health conditions, maintaining a nutritious diet provides a first line of defence against infection and illness. Incorporating whole foods and beneficial fruit, vegetables, dairy, and eggs can reduce the risk of developing various conditions and lessen their severity if they do occur.