8-1- Fermented vegetables and Kimchi
It is tempting to propose that countries where traditional LAB-fermented vegetables are largely consumed are those showing lower COVID-19 death rates and that fermented vegetables represent one possible preventive approach. Other nutrients are found in these products that may enhance their effect (e.g. vitamin K 122). Kimchi fermented from many vegetables including cabbage has several effects on insulin resistance associated diseases: anti-diabetic properties,123,124 cardiovascular diseases, 25dyslipidemia 125 or ageing. 126Kimchi, when fermented for a long time, reduces insulin intolerance to a greater extent than fresh kimchi, 123 indicating that newly formed products during fermentation are important. In particular, Kimchi from cabbage and Chinese cabbage contains several glucosinolates127-129 that can be transformed in sulforaphanes either in the plant itself or by the human microbiome.57 In central European countries, raw and fermented cabbage is commonly consumed.
In Sub-Saharan Africa, people commonly eat fermented foods, mainly cereal-based foods like sorghum, millet and maize, roots such as cassava, fruits and vegetables.
It is clear that sauerkraut is consumed in Alsace (France) where a COVID-19 outbreak has been identified, but it is not a regular meal.
8-2- Westernized diet
Westernized diets contain a reduced amount of fermented vegetables40,130 and may be prone to increasing insulin resistance 41,131 and diseases associated with it,132 and thereby severe COVID-19.
In the Mediterranean diet, well known for reducing insulin resistance,133 Nrf2 appears to play an important role.68,134 The COVID-19 death rate differences in Italian (Figure 2) and Spanish 2 regions suggest a role for Mediterranean diet and short chain food supply. This also indicates that many foods can have an effect and that cabbage and fermented foods represent a proof-of-concept. Nrf2 is also involved in the Okinawan-based diet 68, active on insulin intolerance.135 Taken altogether, it is possible that diet is partly involved in the COVID-19 death clusters found in large Western cities where traditional diet is often replaced by long chain food supply.