Bacteria is linked to metabolic diseases

Obesity and diabetes are common heritable diseases, but the risk of disease lies in complex interactions between our genes, our environment, and our gut bacteria. Our relationship to microorganisms can be simply put as complicated. While some microorganisms can cause deadly infections, others play essential roles in human health. Gut ‘microbiota’ refers to microorganisms that reside in the human gastrointestinal tract, where they ferment undigested carbohydrates, absorb fatty acids, synthesize vitamins, and metabolize bile salts. It is estimated that the human digestive tract has as many as 100 trillion microorganisms-10 times more than the number of cells in the human body! Gut microbiota is dominated by two bacterial phyla, Firmicutes and Bacteroidetes. There is increasing evidence that the balance of these bacterial populations is an important determinant of human health and that disruptions are associated with metabolic diseases like obesity.

Microbiome causes obesity

It has long been established that complex diseases such as obesity are caused by the interplay of our genes with our environment, but recent studies are adding the microbiome to that equation. The microbiome refers to the collective genomes of the microbiota, and its contribution to disease has become an area of intense research. Studies from the lab of Dr. Jeffrey Gordon have linked differences in the ratios of Firmicutes and Bacteroidetes to obesity in mice. They compared lean and obese mice that were fed the same polysaccharide rich diet and found that obese mice has a 50% decrease in Bacteroidetes and a corresponding increase in Firmicutes in their intestines [1]. Interestingly, they also found that colonization of germ-free mice with ‘obese’ microbiota resulted in an increase in body fat when compared to colonization with ‘lean’ microbiota. Furthermore, the researchers found that the microbiome in obese mice was linked to increased energy harvesting from the diet: Firmicutes help to release more nutrients from food while Bacteroidetes consume more nutrients by themselves [2].

Microbiome is also responsible for type 2 diabetes

The relationship between the microbiome and disease is not only limited to obesity but may also have important consequences for the development of type 2 diabetes. A study of the Chinese population found that people with type 2 diabetes had a lower level of butyrate-producing bacteria and a higher level of opportunistic pathogens. These researchers also identified a set of microbiome gene markers that could be used to classify people with the disease and found an enrichment of genes involved in the transport of sugars [3]. Similarly, a study examining a Swedish cohort also identified differences in the microbiome of women with type 2 diabetes and an enrichment of genes associated with glucose metabolism [4].

Can we manipulate the microbiome in people with a disease?

Perhaps in the future this could be a viable option, but there is still much that remains unclear including whether an altered microbiome is a cause or effect of obesity and type 2 diabetes. In the more immediate future, the microbiome may be a useful diagnostic tool that could be used to identify people at risk for developing disease or could be used to guide treatments, and with the decreasing costs of DNA sequencing this may become common practice. Those of us looking to take action now may want to consider the possible benefits of simple probiotic supplements.


If you would like to learn more about disease prevention, continue reading this related blog post: “Can a Salty Diet Lead to Autoimmune Diseases?”.

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  1. Larsen, N., Vogensen, F.K., van den Berg, F.W., Nielsen, D.S., Andreasen, A.S., Pedersen, B.K., Al-Soud, W.A., Sorensen, S.J., Hansen, L.H., and Jakobsen, M. (2010). Gut microbiota in human adults with type 2 diabetes differs from non-diabetic adults. PloS one 5, e9085.
  2. Ley, R.E., Backhed, F., Turnbaugh, P., Lozupone, C.A., Knight, R.D., and Gordon, J.I. (2005). Obesity alters gut microbial ecology. Proceedings of the National Academy of Sciences of the United States of America 102, 11070-11075.
  3. Qin, J., Li, Y., Cai, Z., Li, S., Zhu, J., Zhang, F., Liang, S., Zhang, W., Guan, Y., Shen, D., et al. (2012). A metagenome-wide association study of gut microbiota in type 2 diabetes. Nature 490, 55-60.
  4. Turnbaugh, P.J., Ley, R.E., Mahowald, M.A., Magrini, V., Mardis, E.R., and Gordon, J.I. (2006). An obesity-associated gut microbiome with increased capacity for energy harvest. Nature 444, 1027-1031.
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