Effect of Overgrowth or Decrease in Gut Microbiota on Health and Disease

The composition and function of the gut microbiota develop with their host from birth. The human microbiome, especially the gut microbiota, plays a critical role in a myriad of health and normal activities. However, the increase or decrease in number of gut bacteria may cause several disorders. This review aimed to assess the importance of human gut microflora and their roles in the health and possible diseases caused by fluctuations in the number of these bacteria. For the current review, we searched for the terms “bacterial gut flora”, “role,” “number,” and “increase” and “decrease” on the Google scholar, PubMed, Science Direct, SciVerse, and Scopus search engines and databases. The exclusion criteria were “genetic factors,” “veterinary flora,” “protozoal flora,” “mold,” “fungal,” and “yeast flora”. The gut microbiota is accompanied by the regulation of several host metabolic pathways, giving rise to interactive host-microbiota signaling, metabolic, and immune-inflammatory responses that physiologically connect the gut, muscle, liver, and brain. A more thorough understanding of these axes is an early essential for reaching therapeutic strategies to use the gut microbiota for combating disease and improving health. Bacterial species of Bacteroides, Clostridia, and Bifidobacterium consist of a large proportion of the gut bacterial flora. Increase in the proportion of these genera in the gut could cause abscess formation, sepsis, inflammatory bowel disease (IBD), Crohn’s disease, toxicity, infection, and malnutrition. However, the decrease in the proportion of these species is accompanied by allergies in infants, inflammation, malabsorption syndrome, carbohydrate/fiber intolerance, atopic eczema, and IBD. The results showed that although the human gut microbiome plays a pivotal role in health in a normal concentration, fluctuation in their number (increase or decrease) is a possible factor in the appearance of major diseases.