PYY and obesity due to melanocortin 4 receptor deficiency: Specifically, a previous study demonstrated that the commensal Hafnia alvei reduced body weight gain and fat mass in obesity models, as well as food intake in hyperphagic obese mice, through the production of ClpB protein—a bacterial heat-shock protein that antagonizes α-melanocyte-stimulating hormone (α-MSH), affecting the release of satiety-related hormones such as GLP-1 or Peptide YY in the intestine [31,33].