Background: Recent studies have shown that obesity is associated with the severity of coronavirus disease (COVID-19). We reviewed clinical studies to clarify the obesity relationship with COVID-19 severity, comorbidities, and discussing possible mechanisms.

Materials and methods: The electronic databases, including Web of Science, PubMed, Scopus, and Google Scholar, were searched and all studies conducted on COVID-19 and obesity were reviewed. All studies were independently screened by reviewers based on their titles and abstracts.

Results: Forty relevant articles were selected, and their full texts were reviewed. Obesity affects the respiratory and immune systems through various mechanisms. Cytokine and adipokine secretion from adipose tissue leads to a pro-inflammatory state in obese patients, predisposing them to thrombosis, incoordination of innate and adaptive immune responses, inadequate antibody response, and cytokine storm. Obese patients had a longer virus shedding. Obesity is associated with other comorbidities such as hypertension, cardiovascular diseases, diabetes mellitus, and vitamin D deficiency. Hospitalization, intensive care unit admission, mechanical ventilation, and even mortality in obese patients were higher than normal-weight patients. Obesity could alter the direction of severe COVID-19 symptoms to younger individuals. Reduced physical activity, unhealthy eating habits and, more stress and fear experienced during the COVID-19 pandemic may result in more weight gain and obesity.

Conclusions: Obesity should be considered as an independent risk factor for the severity of COVID-19. Paying more attention to preventing weight gain in obese patients with COVID-19 infection in early levels of disease is crucial during this pandemic.