The gastrointestinal (GI) microbiome remains an emerging topic of study and the characterization and impact on human health and disease continue to be an area of great interest. Similarly, the coronavirus disease 2019 (COVID-19) pandemic has significantly impacted the healthcare system with active disease, lasting effects, and complications with the full impact yet to be determined. The most current evidence of the interaction between COVID-19 and the GI microbiome is reviewed, with a focus on key mediators and the microbiome changes associated with acute disease and post-acute COVID-19 syndrome (PACS).

The novel coronavirus disease-2019 (COVID-19) has created a major public health crisis. Various dietary factors may enhance immunological activity against COVID-19 and serve as a method to combat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The dietary factors that are responsible for boosting immunity may provide a therapeutic advantage in patients with COVID-19. Investigators have demonstrated that vitamins B6, B12, C, D, E, and K, and trace elements like zinc, copper, selenium, and iron may serve as important tools for immunomodulation. Herein this is a review the peer-reviewed literature pertaining to dietary immunomodulation strategies against COVID-19. This review is intended to better define the evidence that dietary modifications and supplementation could positively influence the proinflammatory state in patients with COVID-19 and improve clinical outcomes. With appropriate insight, therapeutic interventions are discussed and directed to potentially modulate host immunity to mitigate the disease mechanisms of COVID-19.

Inflammatory bowel disease (IBD) is a multifactorial chronic disease. Patients with IBD have an increased risk of developing colorectal cancer which has become a major health concern. IBD might exert a role of engrams for making the condition of specific inflammation in the gut. Dysregulation of immune cells induced by the command of engrams might be crucial in the pathogenesis of damages in gut epithelium. The anti-proliferative (APRO) family of anti-proliferative proteins characterized by immediate early responsive gene-products that might be involved in the machinery of the carcinogenesis in IBD. Herein, it is suggested that some probiotics with specific bacteria could prevent the development and/or progression of the IBD related tumors. In addition, consideration regarding the application of studying APRO family proteins for the comprehension of IBD related tumors has been presented. It is hypothesized that overexpression of Tob1, a member of APRO family proteins, in the epithelium of IBD could suppress the function of adjacent cytotoxic immune cells possibly via the paracrine signaling.

The brain and gut are connected both physically and biochemically. The gut-brain axis includes the central nervous system, neuroendocrine and neuroimmune systems, the enteric nervous system and vagus nerve, and the gut microbiome. It can influence brain function and even behavior, suggesting that dietary interventions may help enhance and protect mental health and cognitive performance. This review focuses on the role of the microbiome and its metabolites in sleep regulation, neurodegenerative disorders, mechanisms of stress, and mood. It also provides examples of nutritional interventions which can restore healthy gut microbiota and aid with risk reduction and management of many disorders related to mental and cognitive health. Evidence suggests a shift in the gut microbiota towards a balanced composition could be a target to maintain brain health, reduce stress and improve quality of life.