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Microbes & Immunity Management of obesity

activation. Psychological stress can trigger hedonic Several factors influence early microbiota development,
signaling pathways, leading to increased consumption of including mode of delivery, maternal microbiota, feeding
high-calorie foods. In addition, bacterial fermentation practices, antibiotic exposure, and dietary changes. The
products, such as propionate have been linked to reduced maternal gut microbiota directly affects infant colonization,
reward responses to unhealthy food, thereby influencing with Bifidobacteria being a dominant species transmitted
feeding behavior. 55 through breast milk and fecal matter. Mode of delivery
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also plays a significant role in microbiota composition, with
8.7. Chronic inflammation vaginally born infants showing higher levels of Bacteroides,
Chronic low-grade inflammation is a key trait of obesity, while Cesarean-section-delivered infants exhibit increased
primarily driven by increased levels of LPS – endotoxins levels of Hungatella. Feeding practices shape microbial
released by Gram-negative bacteria, such as Veillonella. In diversity – formula feeding leads to greater microbiome
obese individuals, excessive LPS disrupts the gut barrier development compared to breastfeeding. In addition,
by activating the TLR4/myeloid differentiation primary antibiotic use rapidly alters the gut microbiota, reducing
response 88 (MyD88)/IL-1 receptor-associated kinase 4 beneficial bacterial populations, while dietary changes,
(IRAK4) signaling pathway, allowing bacterial byproducts such as the introduction of complementary foods, further
to enter the bloodstream. Reduced levels of A. muciniphila, influence microbiome diversity. 58
which helps maintain gut barrier integrity, further
contribute to this process. In addition, high-fat diets (HFD) 9.2. Composition of the adult microbiota
facilitate LPS absorption and transport into circulation In healthy adults, the gut microbiota is comparatively
through chylomicrons. Once in the bloodstream, LPS stable, unlike in infants, whose microbiome is still
triggers immune responses in adipose tissue and the liver. developing, and the elderly, who tend to have a less
It forms complexes with LPS-binding protein and cluster diverse and more unstable gut microbiome (Figure 2). The
of differentiation 14, leading to the stimulation of nuclear dominant bacterial phyla in the adult gut microbiota are
factor kappa B (NF-κB) and activator protein 1, which Firmicutes and Bacteroidetes, alongside other phyla, such as
drive the release of pro-inflammatory cytokines, such Actinobacteria, Verrucomicrobia, and Proteobacteria. While
as TNF-α, IL-6, and monocyte chemoattractant protein microbial diversity varies among individuals, gut bacteria
(MCP) 1. These cytokines, in turn, stimulate adipocytes consistently perform essential physiological functions,
to secrete additional inflammatory signals, exacerbating including metabolism, fermentation, methanogenesis, and
metabolic dysfunction. Despite the inflammatory effects of immune regulation. 59
LPS, SCFAs – especially butyrate – exert anti-inflammatory However, several factors can disrupt microbiota
properties. Butyrate promotes IL-18 secretion, supports homeostasis, including host genetics, diet, medications,
regulatory T cell differentiation, and suppresses NF-κB infections, and circadian rhythm disturbances. Diet-
activation, thereby reducing inflammation. However, induced obesity is associated with shifts in microbiota
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it remains unclear whether these beneficial effects are composition that differ from those of normal-weight
sufficient to counteract LPS-induced chronic inflammation, individuals. Antibiotics and other xenobiotics can rapidly
indicating the need for further research. alter microbiome diversity and function, and prolonged
9. Factors affecting homeostasis exposure may lead to antibiotic resistance and microbiome
imbalance. Maintaining a stable microbiota is critical for
9.1. Composition of infants’ microbiota immune system homeostasis, as it helps resist pathogenic
The composition and development of the infant gut infections; however, infections can significantly disrupt
microbiota differ significantly from that of adults, microbiota composition. In addition, circadian rhythm
undergoing a dynamic process of establishment. plays a role in microbiota balance – disruptions in feeding
Colonization begins at birth, with some evidence suggesting patterns can lead to gut flora imbalances and metabolic
maternal bacterial transmission may occur during gestation. disorders, including obesity. Overall, maintaining gut
In neonates, the gut microbiota consists primarily of microbiota stability is essential for supporting metabolic
Enterococcus, Escherichia/Shigella, Streptococcus, and Rothia health and immune function, with various internal and
species, while infants aged 1 – 6 months show increased external factors influencing its composition and resilience. 60
colonization of Bifidobacterium and Collinsella. By 10. Alteration of gut microbiota by
4 months of age, additional bacteria, such as Lactobacillus,
Granulicatella, and Veillonella become prevalent, although antibiotics leading obesity
full microbiome maturation continues until at least two Diet and antibiotics play a fundamental role in shaping
years of age, reaching adult-like complexity by age three. gut microbiota composition, with diet exerting a more

Volume 2 Issue 4 (2025) 48 doi: 10.36922/MI025160036