Antiviral Diet

The immune system is the defense system of the human body. It consists of several smaller systems that work together as an integrated network to clear harmful materials and fight off invading pathogens, such as viruses. Viruses are small parasites that can only live and reproduce inside living cells. They infect host cells so they can transfer their genome using the cells’ machinery to produce more viruses.

A healthy immune system typically elicits an inflammatory response that helps fight off invading pathogens, causing symptoms seen during a viral infection like fever, headache, nasal congestion, and runny nose (i.e., rhinorrhea). The immune system uses different immune cells with antiviral activity (e.g., white blood cells) to fight these viral infections. The two main white blood cells that work against viruses are cytotoxic T lymphocytes, which recognize infected cells and send signals to destroy them, and natural killer cells, which are cells that release substances that kill the infected cells. 

Other important players in the fight against viruses are interferons. These are signaling proteins produced by infected cells, immune cells, and other cells, such as fibroblasts and epithelial cells. Interferons have several functions that aid the immune system in fighting viral infections by activating natural killer cells to kill the infected cells and acting on neighboring cells to improve resistance to the viral infection. Additionally, they act on the virus-infected cells in two ways: downregulating protein synthesis, thereby making viral replication more difficult, and facilitating the immune system's recognition of the infected cells. 

An antiviral diet is a diet that consists of foods that studies suggest have antiviral properties that can enhance the immune response against viral infections. It is not a particular diet that is followed all the time but refers to the integration of functional foods to boost immunity during a viral infection, possibly reducing the severity and duration of the infection.

Some special diets, such as the vegetarian diet, the Nordic diet, or the Mediterranean diet, are particularly rich in antiviral components, as they consist of several key nutraceuticals (i.e., whole or partial food products that possess medical or health benefits), including, flavonoids, pigments, unsaturated fatty acids, vitamins, minerals, and trace elements, such as zinc and iron.

An optimal antiviral diet contains various immune-boosting foods combined with exercise to maximize overall health and prevent communicable and non-communicable diseases.

Antiviral food can enhance immunity by modulating immune function and the life cycle of the viruses, thereby helping reduce the viral load, which is the amount of virus in an infected person’s blood. 

For example, among other viruses, influenza may cause oxidative stress, an imbalance between the number of reactive oxygen species (ROS) and the body’s ability to neutralize them. ROS are highly reactive molecules that can damage cells and tissues; neutralizing these substances is important to restore this balance. Quercetin, a plant pigment from the flavonoid class found in many fruits and vegetables, including onion, asparagus, and berries, is a known antioxidant that can oppose the oxidative stress created by certain viruses.  In addition, various berry extracts can inhibit or reduce the replication of several viruses, including respiratory syncytial virus, influenza virus, herpes simplex virus, and adenovirus.

Vitamin A and zinc are other micronutrients that play a role in the proliferative response of the immune system by increasing the body’s production of white blood cells. Zinc, in particular, is a trace element that assumes numerous roles in the immune system, including acting as a structural part of many proteins and a cofactor for various enzymes. Sources of vitamin A include liver, fish, eggs, dairy products, and orange and yellow vegetables, while the best sources of zinc include meat, fish, and seafood. 

Vitamins C and D are additional important vitamins for the immune response against viral infections. Vitamin C, found in citrus fruit, red or green peppers, and kiwi, may reduce the likelihood of getting lower respiratory tract infections. On the other hand, Vitamin D might be helpful for upper respiratory tract infections, like influenza, by boosting the ability of monocytes and macrophages to fight off the pathogen. Vitamin D is mostly obtained through exposure to sunlight; however, a small number of foods (e.g., cod liver oil,  beef liver, cheese, and egg yolks) are also rich in vitamin D. 

Of note, many studies have been conducted to understand better the effects of various food materials on the immune system and viral infections. However, most studies have been conducted in vitro or on animal models. While additional research with human subjects needs to be performed, integrating functional foods into the diet may help the body fight against infections. 

Various foods are believed to contain potentially immune-boosting components and have antiviral effects against several viruses. Some foods that boost the immune system include traditional herbal medicine, such as mushrooms, roots, red ginseng, licorice, and chlorella, a genus of green algae. Foods containing phenolic compounds and possibly other nutraceuticals that boost the antiviral response include coffee, olive oil, and some berry extracts (e.g., strawberry, raspberry). In addition, traditional foods of the Mediterranean diet (e.g., dairy products, fruits, vegetables, seeds, and oily fish) that are all rich in unsaturated fatty acids contain vitamins, minerals, and essential trace elements with antiviral properties. Peptides and certain amino acids in protein-rich foods, like red meat, chicken, and seafood, are an important energy source and essential for immune cell functions. Lastly, fermented foods and probiotics (e.g., yogurt, kefir, and pickled products) have antiviral benefits. Two species of bacteria studied include Lactobacillus plantarum, found in fermented foods such as Korean kimchi, pickles, and brined olives, and Bacillus subtilis var. Chungkookjang, which is present in a fermented Korean soybean paste called Chungkookjang.

To optimize the immune response to viral infections, foods, and beverages that interfere with the immune system and are generally low in nutrients should be avoided or limited. Alcohol is particularly harmful as it modulates antiviral and inflammatory functions. Both acute and chronic alcohol consumption impairs the immune response, for example, by inhibiting interferons. Ultimately, alcohol increases susceptibility to various viral infections, including hepatitis B virus, hepatitis C virus, human immunodeficiency virus (HIV), and respiratory tract infections. Junk food (i.e., foods high in calories from sugar, fat, or both with little nutritional value) and processed food are also disfavored on an antiviral diet, as they contain less beneficial nutrients to the immune system compared to whole foods. Sugary foods and soft drinks may also contribute to inflammation and weaken the immune system and should be restricted. 

An antiviral diet refers to integrating foods with antiviral properties into a person’s diet. While there is limited scientific evidence to support this diet’s effectiveness in preventing or treating viral infections, some studies suggest that functional foods with antiviral activity can help boost one’s immune functions against several viral infections through various mechanisms. The antiviral diet includes foods containing key nutraceuticals, such as vitamins, minerals, and trace elements found in various fruits, vegetables, nuts, fish, meat, dairy products, and probiotics. Conversely, foods and drinks that should be avoided or limited on an antiviral diet, as they interfere with the immune function, are mainly alcohol, processed food, and sugary food and beverages.