Allergy, atopic diseases, and chronic inflammatory conditions like ulcerative colitis have significantly increased over the past 60 years. This rise has occurred alongside improvements in quality of life but also shifts in lifestyle and environmental factors. Many hypotheses have been proposed to explain this increase, including the hygiene hypothesis, the biodiversity hypothesis, and the epithelial barrier hypothesis. These theories suggest that inhabitants in modern, Westernized societies are exposed to declining environmental biodiversity, excess lifestyle chemicals and air pollution, antibiotics, and highly processed foods, as well as decreased dietary fiber intake. The absence of fiber prompts bacteria to target the topmost layer of the gut mucosal barrier, known as mucus, for sustenance, contrary to their typical reliance on fiber. Various factors, including short-chain fatty acids, play a role in this process. The lack of fiber and dysfunction of the mucous barrier, often termed “leaky gut”, have profound impications for overall human health and well-being.