Individual diet plays a significant role in affecting immune response and COVID-19 susceptibility. On the molecular level, certain intake of nutrients can contribute to the activation of certain helper T-cells, B-cells, etc. as well as secretion of signaling molecules like transcription factors that can modulate gene expression. For instance, high consumption of red meat, high glycemic index (GI) food, and high fat often lead to accumulation of visceral fat that causes hormonal imbalances in cytokines secretions. One common effect is chronic expression of pro-inflammatory cytokines like TNFα, IL-1β, and IL-6. Long-term expression of these cytokines triggers increase of Leptin, a downstream cytokine that serves as a positive feedback loop in further enhancing the expression of TNFα, IL-1β, and IL-6. Expression of these cytokines has found to be involved with decreased T-cell population, which explains why this kind of diet increased susceptibility and allergic reactions as well as poor antibody response, particularly in obese populations. On the microbial level, specific nutrients consumption also play a significant role in shaping the gut microbiome, which can directly influence immune response. Deficiencies in calories, protein, minerals, and vitamins are commonly correlated with suppressed immune surveillance and susceptibility to infection. In the intestinal lumen, various antimicrobial peptides were secreted to impede growth of certain microbe over another. It is evident that to some extent, the gut microbiome has direct interaction with modulating immune homeostasis that finely control pro and anti-inflammatory responses. Microbes play significant roles in fingerprinting microorganism-associated molecular patterns (MAMPs) and pathogen-associated molecular patterns (PAMPs). A typically healthy gut microbiome will contain some of the common bacterial taxonomies like lactobacillus, bacteriodes, and bifidobacteria that secrete certain metabolites and other immune-modulatory signals that often contain short chain fatty acids (SCFA) like acetate and butyrate. These molecules can bind to certain receptors like toll-like receptors of innate cells that can have effect on their metabolism and activity.