Feasting for immunity: Study highlights foods that bolster your body's defenses

By Priyanjana Pramanik, MSc.Nov 26 2023Reviewed by Susha Cheriyedath, M.Sc.

In a recent review in the journal Food Science & Nutrition, a team of researchers summarized the current medical knowledge regarding the role certain common foods play in strengthening the immune system. The comprehensive article covered the benefits of consuming fruits, vegetables, spices, animal products, and other foods in maintaining a healthy immune system.

Study: Common foods for boosting human immunity: A review. Image Credit: Danijela Maksimovic / Shutterstock

Background

The human immune system protects the body from pathogenic invasions. Humans are born with innate immunity (with cells such as macrophages and neutrophils). Some immunity (such as some types of white blood cells or lymphocyte cells) is acquired through exposure to pathogens. However, scientists have known for a long time that a healthy diet is critical for maintaining and improving immunity. A dysfunctional immune system can lead to issues such as bronchial asthma, cystic fibrosis, and fibromyalgia.

Immune cells require sufficient energy to function, while micro- and macronutrients maintain immune response. While the immunological function of specific nutrients such as vitamins, minerals, and fibers has been reviewed in previous research, the immune benefits of specific food items have not been explored. In this review, the research team set out to address this gap, documenting commonly available foods that can boost immunity and build resistance to disease.

Immune System and Nutrition

In humans, the immune response primarily comes from active immunity, in which antibodies are produced within the body. In addition to immune cells, other components 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, are classified as immunoglobulins A (IgA), D (IgD), E (IgE), G (IgG), and M (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 such as the spleen filter infections and abnormal cells in the blood, while glands can trap germs and other foreign materials.

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

In addition to plant- and animal-based foods, water has a vital 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 them building up in the body and causing illness. Drinking sufficient quantities of water can also prevent urinary tract infections by stopping kidney stone formation.

Inadequate nutrient consumption can weaken the immune system's development 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. 

The researchers conducted a literature search on major scientific databases such as PubMed, Web of Science, and Scopus to identify studies that focused on the immunomodulatory properties of common foods. These included peer-reviewed literature such as research papers, meta-analyses, and systematic reviews.

Foods and nutrients that boost immunity

Citrus fruits such as 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 immune response, while retinoic acid promotes lymphocyte growth at infection and inflammation sites in the stomach.

Similarly, kiwis also contain vitamin C, K, potassium, carotenoids, fibers, and antioxidants; they are anti-inflammatory foods that can reduce the risk of developing the flu. Pomegranate has 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, essential amino acids, and micronutrients. Prolactin, 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, but calcium can be absorbed more efficiently 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. Eggs are an affordable source of protein for those who cannot access pulses and dairy.

While medicine is critical in healing from health conditions, maintaining a nutritious diet provides a first line of defense 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.