Gut Bacteria & Your Waistline

As expanding waistlines continue to threaten Asia, Ivan Seah examines a surprising link between obesity and the bacteria that inhabit our gut.

AsianScientist (Apr. 16, 2015) – Obesity is a growing problem. According to the World Health Organization, the incidence of obesity worldwide has doubled since 1980. It is predicted that by 2030, about 58 percent of the world’s adult population might either be overweight or obese.

In the Asia Pacific region, cardiovascular experts have warned of a rising epidemic of obesity. For example, between the 1980s and 2000s, obesity rates increased from 17 to 24 percent in Japan and from 4 to 19 percent in China.

“In many of the countries in Asia Pacific, the malnutrition problem nowadays is not undernutrition; It is overnutrition that has resulted in overweight and obesity,” said Professor Sim Kui-Hian, President Elect of the Asian Pacific Society of Cardiology, at the 19th Asian Pacific Congress of Cardiology.

“The Asian culture revolves around food as a way of showing hospitality because in the past there was a lot of famine. As a result there is a cultural perception that if you’re not fat or obese then you are not well off,” he explained.



Have you got the gut (flora)?

While the onset of obesity was always thought to be due to factors such as a lack of exercise, excessive food intake and genetic susceptibility, the exact mechanisms have remained a mystery. Interestingly, a recent report by the University of North Carolina (UNC) School of Medicine in the US suggests that gut bacteria may actually play a role in the pathogenesis of obesity.

The human body plays host to various ecosystems invisible to the naked eye. On our skin and in our mouth and gut, many microscopic organisms flourish and enjoy a mutualistic relationship with us. In a recent TED talk, Princeton University molecular biologist Dr. Bonnie Bassler compared the approximately one trillion human cells found in the average human to the more than ten trillion bacteria that co-exist with them.

Populated by over 1,000 different species of bacteria, the gut is the largest reservoir of human flora. Research has shown that gut bacteria are involved in a multitude of functions, including carbohydrate fermentation, immunity promotion and metabolic function. However, this is only the tip of the iceberg.

The diversity of gut flora can transform according to environmental changes. This means that diet and stress levels of an individual can change the composition of gut bacteria, resulting in alterations to metabolic pathways. Hence, it is becoming increasingly important for scientists to understand this intimate yet complex relationship between gut bacteria and the human body.

The UNC study demonstrated that certain populations of gut bacteria could increase the absorption of dietary fats, allowing the host to extract more calories from the same amount of food. Using the zebrafish as a model, the researchers found that a particular phylum of bacteria, Firmicutes, is crucial in the regulation of fat absorption, indicating a role for gut bacteria in weight regulation.

UNC Assistant Professor John Rawls, who led the study, said: “If we can understand how specific gut bacteria are able to stimulate absorption of dietary fat, we may be able to use that information to develop new ways to reduce fat absorption in the context of obesity and associated metabolic diseases, and enhance fat absorption in the context of malnutrition.”

Looking ahead, prophylactic treatments for such diseases may someday be as simple as prescribing antibiotic treatments to change the diversity of the gut ecosystem.


The Need for Action

Aesthetics aside, the real issue with obesity is that it increases the likelihood of diseases such as heart disease, diabetes, joint problems and even cancer. These chronic diseases have shown to be extremely costly for healthcare systems to manage. In many developed nations, it is recognized that if urgent action is not taken to curb obesity in the population, it may have the potential to topple major healthcare systems.

Hence, there is increased interest in uncovering the link between obesity and chronic illnesses. In a recent study reported in the journal Nature, Dr. Hara Eiji and colleagues from the Japanese Foundation for Cancer Research in Tokyo made the surprising discovery that obesity may be linked to hepatocellular carcinoma, the most common type of liver cancer, through a change in the composition of gut bacteria.

In their study, mice exposed to carcinogenic elements were fed either a normal or high-fat diet to induce obesity. Five percent of the mice fed a normal diet developed cancer in the lung, while all the obese mice developed liver cancer. Interestingly, the researchers discovered that obese mice had a greater number of Clostridium bacteria, which are responsible for producing deoxycholic acid (DCA), a chemical that causes DNA damage and induces cell senescence. As DCA circulates in the liver, it induces changes in liver cells, causing them to secrete various inflammatory and tumor promoting factors.

Importantly, the researchers found that blocking DCA production or reducing Clostridium numbers by treatment with vancomycin, an antibiotic that targets gram-positive bacteria, could reduce the development of liver cancer in obese mice.

“Obesity in general has many different types of cancer associated with it. But in the case of liver cancer, I never expected the microbiome to be linked,” said Hara.

Like any good scientific mystery, the links between gut bacteria and our health are obscure and usually realized in the most unexpected manner. The gut, along with its trillions of residents, continues to harbor a degree of complexity comparable to studying a forest worth of organisms and their relationships with each other.

Research on the gut microbiome is still in its infancy and there is much we do not know about these bugs that reside within us. However, as the role of each bacterium in the gut is defined, pieces of the obesity puzzle may slowly be uncovered.

Perhaps in the near future, combating obesity will no longer involve the immense determination and discipline required to exercise and eat healthy. Instead, it could very well be as simple as taking a pill to rebalance your gut microbiota.


This article was first published in the print version of Asian Scientist Magazine, Jan 2014.

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Ivan Seah Yu Jun is a medical student at the University of Glasgow Wolfson Medical School in the UK.

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