The term "infectobesity" refers to the hypothesis that

obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's ...

in humans can be caused by pathogenic organisms, and the emerging field of medical research that studies the relationship between

pathogens In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a ger ...

and weight gain. The term was coined in 2001 by Dr. Nikhil V. Dhurandhar, at the Pennington Biomedical Research Center.

Bacteria

The study of the effect of infectious agents on metabolism is still in its early stages. Gut flora has been shown to differ between lean and obese humans. There is an indication that gut flora in obese and lean individuals can affect the metabolic potential. This apparent alteration of the metabolic potential is believed to confer a greater capacity to harvest energy contributing to obesity. Whether these differences are the direct cause or the result of obesity has yet to be determined unequivocally. A possible mechanistic explanation linking gut flora to obesity involves

short chain fatty acids Short-chain fatty acids (SCFAs) are fatty acids with fewer than six carbon atoms. Derived from intestinal microbial fermentation of indigestible foods, SCFAs are the main energy source of colonocytes, making them crucial to gastrointestinal health. ...

. Humans are unable to digest complex

polysaccharides Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with w ...

and rely on gut microbiota to ferment these polysaccharides into short chain fatty acids. In contrast to polysaccharides, humans can use short chain fatty acids as a source of energy. In addition, research in rodents has indicated that the abundance of short chain fatty acids in the gut can affect the blood levels of gut hormones such as

GLP-1 Glucagon-like peptide-1 (GLP-1) is a 30- or 31-amino-acid-long peptide hormone deriving from the tissue-specific posttranslational processing of the proglucagon peptide. It is produced and secreted by intestinal enteroendocrine L-cells and certa ...

GLP-2 Glucagon-like peptide-2 (GLP-2) is a 33 amino acid peptide with the sequence HADGSFSDEMNTILDNLAARDFINWLIQTKITD (see Proteinogenic amino acid) in humans. GLP-2 is created by specific post-translational proteolytic cleavage of proglucagon in a process ...

and

peptide YY Peptide YY (PYY) also known as peptide tyrosine tyrosine is a peptide that in humans is encoded by the gene. Peptide YY is a short (36-amino acid) peptide released from cells in the ileum and colon in response to feeding. In the blood, gut, a ...

. These changes in gut hormone levels have shown to affect

glucose tolerance Prediabetes is a component of the metabolic syndrome and is characterized by elevated blood sugar levels that fall below the threshold to diagnose diabetes mellitus. It usually does not cause symptoms but people with prediabetes often have obesit ...

, insulin signaling, intestinal barrier function and have led to weight gain in rodents. Dietary diversity is associated in humans and animals with a more healthy gut microbiota, and thus may be necessary for effective long-term health improvement strategies, but is often overlooked in animal studies. Furthermore, administration of antibiotics to rodents alters gut microbiota composition and ensuing changes in gut hormone levels are also detected. These results may provide the mechanistic explanation for the claim that antibiotics can lead to obesity in humans. Yet, whether these findings can be replicated in human studies remains to be seen.

Viruses

An association between

viruses A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's ...

and obesity has been found in humans, as well as a number of different animal species. The amount that these associations may have contributed to the rising rate of obesity is yet to be determined. A fat virus is the popular name for the notion that some forms of obesity in humans and animals have a viral source.

References

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External links

Infectobesity: obesity of infectious origin. Adv Food Nutr Res. 2007 52: 61–102

��Article in ''The New York Times Magazine'', August 13, 2006

��Article on ''MotleyHealth.com'', August 15, 2009 Obesity Pathogenic microbes Gut flora

Bacteria

Viruses

See also

References

External links