Photo: Canna, Xavier La. "Gut Organisms Could Be Key to Unlocking Western Diseases." ABC News. N.p., 24 Oct. 2014. Web. 02 Apr. 2017.
Obesity is a major health concern. Nowadays, more than 500 million people are obese worldwide leading to considerable economical costs as well as public health challenge. Obesity arises from complex interactions between genes and environmental factors such as diet, food components and/or way of life, and results from a long-term positive imbalance between energy intake and expenditure with excessive increase in body fat (1).
Gastrointestinal disorders resulting from obesity are more frequent and present earlier than type 2 diabetes and cardiovascular diseases. Diseases such as gastroesophageal reflux disease (GERD is a digestive disorder that affects the lower esophageal sphincter which causes heartburn or acid indigestion), cholelithiasis (involves the presence of gallstones that form in the biliary tract, usually in the gallbladder), and non-alcoholic steatohepatitis (liver inflammation and damage caused by a buildup of fat in the liver) are directly related to body weight and abdominal adiposity (2). There is growing evidence that the gut microbiota (bacteria harbouring the gut) and its bacterial genome (the complete set of genes or genetic material present in the bacteria) affect how much of the food we eat are absorbed by the body, energy regulation and fat storage. These findings raise the possibility that the gut microbiota plays a role in regulating host energy metabolism and may contribute towards the development of obesity and associated metabolic diseases.
Adult humans are colonized by microbes from nine divisions (deep evolutionary lineages) of Bacteria and at least one division of Archaea (1). Moreover, three bacterial divisions, the Firmicutes, Bacteroidetes and Actinobacteria (a different type of microbe), dominate the adult human gut microbiota (bacteria that harbours the gut) and account for more than 90 % of all bacteria, whereas Methanobrevibacter smithii, a hydrogen-consuming methanogen (microbes that produce methane), dominates the Archaea domain.
Studies have shown that obese mice as well as humans had different gut microbiota composition compared to lean. A number of studies showed an increase in bacteria from the Firmicutes phyla and a decrease in the Bacteroidetes phyla that is believed to be associated with increased energy absorption from food and increased low-grade inflammation (3). Moreover, other experiments suggest that obesity can influence the composition of gut microbiota. For example, when obese people diet and lose weight, the proportion of Bacteroidetes increases relative to Firmicutes. Bacteria from the firmicutes phyla of bacteria extract short chain fatty acids from dietary fiber at higher rates than other gut microbes. The result is the person harboring more of these microbes gains an extra 150 calories daily. An imbalanced gut ecosystem can cause inflammation throughout the body that slows down the body’s metabolism, induces insulin resistance and leads to fat accumulation (4)
What can you do (4)?
1. Gérard, Philippe. "Gut Microbiota and Obesity." Cellular and Molecular Life Sciences 73.1 (2015): 147-62.
2. Acosta, Andres, and Michael Camilleri. "Gastrointestinal Morbidity in Obesity." Annals of the New York Academy of Sciences 1311.1 (2014): 42-56.
3. Ley, Ruth E., Peter J. Turnbaugh, Samuel Klein, and Jeffrey I. Gordon. "Microbial Ecology: Human Gut Microbes Associated with Obesity." Nature 444.7122 (2006): 1022-023.
4. John, George Kunnackal, and Gerard E. Mullin. "The Gut Microbiome and Obesity." Current Oncology Reports18.7 (2016): n. pag.