Positives

• Both ME/CFS and Long COVID patients show depletion of butyrate-producing bacteria (Eubacterium rectale and Faecalibacterium prausnitzii), and fermented foods help reseed these diversity gaps before the gut is ready to handle high-fiber prebiotics RTHM.
  
  
• A clinical trial titled “Evaluating the Effects of a Fermented Diet on Microbiome Diversity in Individuals With Long COVID” is now underway, with researchers actively soliciting Long COVID patient participation ClinicalTrials.gov.
  
  

Negatives

• A significant percentage of Long COVID patients have small intestinal bacterial overgrowth (SIBO); for them, consuming high amounts of fermented foods can lead to severe bloating, pain, and worsening fatigue rather than benefit RTHM.
  
  

Hurdles & Side Effects

• Patients with MCAS or histamine intolerance often react badly because Lactobacillus casei, L. reuteri and L. bulgaricus convert histidine to histamine during fermentation, raising body histamine load Mast Cell 360.
• Homemade ferments allow control over starter cultures and time, but store-bought sauerkraut and kombucha vary widely in histamine content and live count; patients are commonly advised to start with 1 tsp doses to identify a personal threshold Cultured Food Life.