Functional food: complementary to fight against COVID-19

Abstract

Background: The novel coronavirus has embarked on a global pandemic and severe mortality with limited access for its treatments and medications. For the lack of time, research, and enough efficacy, most vaccines are underdeveloped or unreachable to society. However, many recent studies suggest various alternative, complementary remedies for COVID-19, which are functional foods. This review provides an overview of how functional foods can play a great role through modulating the host immune system, generating antiviral activities, and synthesizing biologically active agents effective against the coronavirus.

Main body: This review article summarizes the natural defense mechanisms in tackling SARS-CoV-2 alongside conventional therapeutic options and their corresponding harmful side effects. By analyzing bioactive components of functional foods, we have outlined its different contributions to human health and its potential immunomodulatory and antiviral properties that can enhance resistivity to viral infection. Moreover, we have provided a myriad of accessible and cost-effective functional foods that could be further investigated to target specific key symptoms of COVID-19 infections. Finally, we have found various functional foods with potent bioactive compounds that can inhibit or prevent COVID-19 infections and disease progression.

Short conclusion: Numerous functional foods can help the body fight COVID-19 through several mechanisms such as the reduced release of pro-inflammatory cytokines, reduced expression of ACE2 receptors in cells, and inhibiting essential enzymes in SARS-CoV-2.

Keywords: Functional food; Immune system; Medicinal plants; Probiotics; Vitamins.

Fig. 1

SARS-CoV-2 infects primarily alveolar cells through the ACE2 receptor. The immune system responds to the virus by activating different transcription factors that release pro-inflammatory cytokines that trigger the accumulation of immune cells leading to antigen presentation. Additionally, secretion of specific cytokines such as IL-8 attracts neutrophils and macrophages to the site of infection alongside T lymphocytes. While neutrophils kill by oxidative burst and NETs with macrophages inducing phagocytosis, CD4 + T cells help to activate B cells producing anti-SARS-CoV-2 and CD8 + T cells kill infected cells through the release of perforins and cytotoxins. If CD8 + T cells fail to kill the virus in the presence of inflammatory cytokines over the long term, cytokine storm occurs, leading to disease progression and complications such as ARDS, organ failure, and death

Fig. 2

Comparison of conventional COVID-19 therapies with functional food therapy. Vaccines and drugs, both part of conventional therapy, pose many challenges such as side effects, inaccessibility, non-specificity, and inaccuracy. In addition, the long-term accuracy and side effects of all COVID-19 vaccines have not been studied, making vaccine treatment very uncertain. In contrast, functional foods are simple, cost-effective food ingredients that are available to everyone. Furthermore, since daily intakes for these foods have been studied rigorously and established, they are safe to consume while providing additional benefits and improving general health

Fig. 3

Proposed mechanisms of COVID-19 treatment by functional foods. Functional foods can alleviate COVID-19 symptoms through their immunomodulatory and antiviral properties. Preventing cytokine storms, elevating numbers of immune cells (T cells & NK cells), reducing ACE2 receptor expression, and inhibiting viral replication through inhibition of viral proteins and enzymes are some of the ways through which functional foods can help improve COVID-19 progression