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Microbes & Immunity Management of obesity

expenditure. Innovative approaches must be developed to 8.2. The functions of gut microbiota: Feeding
determine whether gut bacteria influence thermogenesis behavior and regulation of central appetite
in humans. Dysbiosis suppresses neuropeptide-related The gut microbiota plays a critical part in regulating
52
genes involved in energy homeostasis, including GCG central appetite and feeding behavior through multiple
(encoding preproglucagon) and BDNF (encoding brain- mechanisms, as outlined in the following subsections.
derived neurotrophic factor), and induces leptin resistance
through suppressor of cytokine signaling-3, thereby 8.3. Bacterial metabolites and satiety
exacerbating obesity. The reduction of L. paracasei Certain bacteria (Bifidobacterium, Lactobacillus) produce
removes its inhibition of lipoprotein lipase, allowing lactate, which supports neuronal activity and prolongs
more triglycerides to be absorbed by adipocytes, thereby satiety. SCFAs, such as acetate and butyrate, derived from
facilitating lipid storage (Figure 1).
bacterial fermentation, influence appetite regulation by
8. Feeding behavior and central appetite affecting neuropeptides in the hypothalamus and activating
the vagus nerve.
8.1. The gut–brain axis
8.4. Gut hormones and appetite control
The gut–brain axis is a complex, bidirectional
communication system that transmits nutritional and Intestinal hormones, such as GLP-1 and peptide YY are
metabolic information between the gut and the central produced by enteroendocrine cells and are modulated
neurological system through various pathways, including by bile acids, SCFAs, and indoles. These hormones act as
the vagus nerve, the neural system, and the gut endocrine anorexigenic signals, binding to receptors in neurons, the
system. Recent research has highlighted the significant hypothalamus, and the brainstem to suppress appetite. 54
role of the gut microbiota in this interaction, leading to 8.5. Neurotransmitters and feeding behavior
the concept of the microbiota–gut–brain axis. Studies
suggest that this correlation plays an important in both Gut bacteria contribute to the production of
gastrointestinal and neurological conditions, such as neurotransmitters, including serotonin and GABA, which
Parkinson’s disease and irritable bowel syndrome. Given regulate appetite. GABA stimulates feeding behavior, while
that the gut–brain axis plays a major role in regulating serotonin suppresses appetite by modulating melanocortin
appetite and feeding behavior, disruptions in the gut neurons, which help maintain energy balance.
microbiota (gut dysbiosis) in obese individuals may
impact food intake and contribute to obesity progression. 8.6. Mood and reward pathways
This underscores the importance of gut microbiota in both The gut microbiota influences mood through immune
metabolic and neurological health. 53 responses, microbial metabolites, and vagus nerve

Obesity

Firmicutes/Bacteriodetes
ratio; Clostridium ramosum Lactobacillus
H2-utilizing Archea
Bacteriodes

Energy intake Energy expenditure
CD36, Glut2 TGR5/FXR pathway
Amylases /amylomaltases Uncoupled mitochondrial function
Interspecies H2 transfer Thermogenesis
SCFA production White adipose tissue browning
Catabolic process

Figure 1. Energy homeostasis disruption
Abbreviations: CD36: Cluster of differentiation 36; FXR: Farnesoid X receptor; Glut2: Glucose transporter 2; H2: Hydrogen; TGR5: Takeda G-protein-
coupled receptor 5.

Volume 2 Issue 4 (2025) 47 doi: 10.36922/MI025160036