- Decrease in effector T-cells
-Increased apoptosis in lymphocytes
-  Decrease of B-cells in blood
- Decrease in vaccination titre response

Severe Malnutrition

- Decrease in thymus size
- Increase in Th2 cytokines

Moderate Malnutrition

Proper nutrition is essential for the body to fight off viral infections. Lack of proper nutrition can not only decrease the immune system's ability to fend off infection, but also increase the likelihood of other comorbidities that increase the fatality of COVID-19.

University of California, Davis

University of California, Santa Cruz

- "Western diets" and saturated fatty acids
- High fiber and balanced diets
- Malnutrition 
- Overnutrition
- Noncommunicable Diseases 
- Vitamin D
- Nutrition Therapy in Critically Ill Patients With Coronavirus Disease 2019
- Eucaloric Ketogenic Diet (EKD)
- Nutritional status of patients with coronavirus disease 2019 (COVID-19)
- Easy-to-prescribe nutrition support in the intensive care in the era of COVID-19
- Anti-inflammatory foods 
- Nutrigenomics
- Epigenetics
- Polyphenols
- Gastrointestinal Manifestations of COVID-19
- Vitamin C
- Maternal and child health

Focuses of Effects of human nutrition in fighting COVID-19

Hakeem, R., & Sheikh, M. A. (2020). Beyond transmission: Dire need for integration of nutrition interventions in COVID-19 pandemic-response strategies in Developing Countries like Pakistan. Pakistan Journal of Medical Sciences, 36(COVID19-S4). doi:10.12669/pjms.36.covid19-s4.2784

Beyond transmission: Dire need for integration of nutrition interventions in COVID-19 pandemic-response strategies in Developing Countries like Pakistan

Zabetakis, I., Lordan, R., Norton, C., & Tsoupras, A. (2020). COVID-19: The Inflammation Link and the Role of Nutrition in Potential Mitigation. Nutrients, 12(5), 1466. https://doi.org/10.3390/nu12051466

COVID-19: The Inflammation Link and the Role of Nutrition in Potential Mitigation

Barazzoni R., Bischoff S.C, Krznaric Z., Pirlich M., Singer P.  ESPEN experts statements and practical guidence for nutritional management of individuals with SARS-CoV-2 infection. Clin Nutr. 2020 doi: 10.1016/j.clnu.2020.03.022.

ESPEN experts statements and practical guidence for nutritional management of individuals with SARS-CoV-2 infection.

A Western Diet is high in saturated fatty acids, refined carbohydrates, and sugars. It is also marked by low consumption of fiber, unsaturated fats, and antioxidants.

Western Diets

The effects of malnutrition on fighting COVID-19

Noncommunicable diseases, also known as chronic diseases, are noninfectious and may be caused by an individual's lifestyle, genetics, or environment. There is a direct link between noncommunicable diseases and the severity of viral infections. 

As such, conditions like high blood pressure and diabetes are thought to exacerbate the severity of COVID-19. Researchers propose the best way to combat COVID-19 for individuals with noncommunicable diseases is based in lifestyle changes, with a focus mostly on diet. See: 

- The Mediterranean Diet 
- Vitamins C, D, and E 
- Zinc, Copper, and Fiber 

Noncommunicable Diseases

As therapeutic interventions remain largely experimental, supportive care in the form of nutrition management is integral for critically ill patients.

Nutrition Therapy in Critically Ill Patients With CoronavirusDisease 2019

High fiber and balanced diets are rich in whole grains, cereals, fruits, vegetables and legumes . 

High fiber and balanced diets 

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. 


Effects of Nutrition and Gut Microbiome on Immune Response to COVID-19

Vitamin D is a nutrient that is both endogenously synthesized in the skin and consumed dietarily.  Its biologically active form [1,25-(OH)2D] is a known negative regulator of the Renin-Angiotensin System (RAS).  1,25-(OH)2D has been shown to increase ACE2 expression and suppress the inflammatory outcomes caused by angiotensin II (Ang II).  Additionally, vitamin D can modulate the immune system by inhibiting B-cell and T-cell proliferation as well as inducing T-regulatory cells, which suppress pro-inflammatory cytokines and increase anti-inflammatory cytokines.  These processes may make vitamin D a useful molecule in treating or preventing a SARS-CoV-2 infection.

Using Vitamin D to Mitigate COVID-19

An imbalanced nutritional status resulting from excessive intake of nutrients generated by an energy imbalance between food consumption and energy expenditure leading to disorders such as obesity.

Overnutrition

Compounds in plants that can have healing and therapeutic properties for treating illnesses or injuries. 


Phytomedicines 

The eucaloric ketogenic diet is a diet consisting of mainly fat and minimal amounts of carbohydrates. It provides the body with sufficient calories while it stabilizes blood glucose levels and reduces oxidative stress.

Eucaloric Ketogenic Diet (EKD)

Among 50 (mean age 52.2, SD 20.7) hospitalized patients with COVID-19, 76% were deficient in vitamin D and 42% in selenium. Among the nutrients zinc, B1, B6, B12, folate, vitamin D, selenium, all the 12 patients with severe respiratory distress and advanced stage of the disease had a deficiency in more than one nutrient .

Nutritional status of patients with coronavirus disease 2019 (COVID-19)

Due to the large influx of Covid-19 ICU patients, a new protocol has been developed to provide easier and simplified nutritional distribution. At the end of the pandemic wave, the protocol was evaluated in the form of questionnaires and surveys. 122 physicians on the ICU medical team received the protocol and a great majority of the medical team as well as the participants assessed it as a useful tool for nutritional therapy.

Easy-to-prescribe nutrition support in the intensive care in the era of COVID-19

Foods used to treat chronic illnesses have shown to improve the health of patients who have COVID-19 as well. Some examples of these foods are:

-Vegetables: Broccoli, kale, Brussels sprouts, cabbage, cauliflower, etc.


-Fruit: Especially deeply colored berries like grapes and cherries


-High-fat fruits: Avocados and olives


-Healthy fats: Olive oil and coconut oil


-Fatty fish: Salmon, sardines, herring, mackerel, and anchovies


-Nuts: Almonds and other nuts


-Peppers: Bell peppers and chili peppers


-Chocolate: Dark chocolate


-Spices: Turmeric, fenugreek, cinnamon, etc.


-Tea: Green tea


-Red wine: Up to 5 ounces (140 ml) of red wine per day for women and 10 ounces (280 ml) per day for men

Anti-inflammatory Foods

SUMMARY OF CURRENT INFO
- Research for ACE1
- Research for AGTR1
- Research for ACE2
- Research for TMPRSS2 and ESR2
- Nutritional strategies

ARTICLES
- Current State of Evidence: Influence of Nutritional and Nutrigenetic Factors on Immunity in the COVID-19 Pandemic Framework

Nutrigenomics

ARTICLES RESEARCHED
- Can Vitamins, as Epigenetic Modifiers, Enhance Immunity in COVID-19 Patients with Non-communicable Disease?
- Epigenetic Diet to Modulate Immune Response against SARS-CoV-2
- The epigenetic implication in coronavirus infection and therapy

Epigenetics

Polyphenols is from plant based food and a potential use for against COVID-19. 

Polyphenols

Even though COVID-19 is primarily viewed as a reparatory illness, it has also been found to affect the gastrointestinal system. Therefore, there is an increasing need for a focus on gastroenterology to establish proper nutrition therapies. To develop these nutrition therapies, a better understanding of preexisting gastrointestinal diseases is vital, as well as consideration of the challenges and obstacles of nutrition therapy.

Gastrointestinal Manifestations of COVID-19: Impact on Nutrition Practices

Vitamin C, ascorbic acid, is a required nutrient for humans that humans are unable to endogenously synthesize.  Therefore, humans are dependent of food and other external sources for sources of vitamin C.
A deficiency of vitamin C has been found to be linked with respiratory infections, and current evidence suggests that 2-8 g/day of oral vitamin C may reduce the incidence and duration of these respiratory infections, including COVID-19.  

Using Vitamin C to mitigate Covid-19

- COVID-19 pandemic and mitigation strategies: implications for maternal and child health and nutrition

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