Can Bacteria Make You Fat?

Jorge Zárate, Co-Editor-in-Chief

We’ve all heard by now about the epidemic spread of obesity in the United States and the world. While only twenty states in the US had obesity prevalence rates of 15% in 1989, not a single state remains with such low rates today – in fact, at least 20 states have rates higher than 30%, according to the Center for Disease Control. An increasingly sedentary lifestyle, increased portion sizes, improvements in technology, and the growing demand for processed foods all share the blame for the increased prevalence of obesity, but there’s another main contributor: bacteria. The link between bacteria and obesity is not completely understood. Bacteria, we believe, affect the efficiency of digestion either by compromising the integrity of the intestinal lining (increasing the amount of nutrients and fat that cross into the bloodstream) or via the production of byproducts, like certain short chain fatty acids, that allow us to yield energy that would otherwise be wasted.

Entire ecological systems of microorganisms (microbiome) live on us; the skin, mouth, gut, and genitalia each have their unique microbial communities. For every one of your cells, there are ten bacterial cells living in and on your body. Research is starting to show that these bacteria play very important roles in the normal functioning of the body. For example, some bacteria are known to “train” the immune system to recognize harmful bacteria and prevent infection. The bacterial communities that we coexist with are very dynamic – their compositions not only vary depending on what part of your body they chose to colonize, but also change depending on your age, the season, and even your lifestyle choices, such as what you eat and whether you smoke. The bacteria in the gut are particularly sensitive to your diet, since different bacteria prefer different nutrients as sustenance.

The research I am part of this summer as part of the Blaser Microbiology Lab at NYU’s Langone School of Medicine focuses on the microbiome that lives in the gut. The microbiome of the gut develops as we age, and the body naturally selects for the bacteria that will become part of the adult microbiome, which can influence adult metabolism. The bacteria our bodies select for depends on several factors, including our diet and our genetic profiles. The natural selection process can also be disrupted by antibiotics; farmers have been using low-dose antibiotics to fatten livestock since the 1950’s.  We do not know yet, however, how antibiotics change these microbial communities, and which microbes could potentially promote or prevent weight gain.

Advancements in technology have provided additional tools, like high-throughput DNA sequencing, that will help us to better understand the microbiome. High-throughput sequencing is a fast method that allows us to examine the composition of microbial communities in hundreds of samples at once. The DNA sequencing machine works by reading the amount of light emitted each time a base (A, T, C, or G) binds to a single-stranded DNA sample – this chemiluminescene allows us to determine the sequence of any DNA samples we provide. Sequencing, when paired with genomic databases, allows us to identify the compositions of bacterial communities in the gut down to the genus level. We can also use these tools to find out how the abundances of certain bacteria change over time and in response to other variables, such as high-fat diet and antibiotics.

Research on the link between the human microbiome and the metabolic imbalances that lead to obesity could help us to pinpoint, one day, exactly how changes in the microbiome affect human metabolism and lead to obesity. This knowledge could help us learn how to restore unhealthy gut communities, allowing us to design a therapy against obesity in a not-so-distant future.

[Photo courtesy of NYU Langone Medical Center]

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