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Gut microbes mix with toxins to make us fat?

CORNELL (US) — Pollutants and chemical toxins could increase the chances of being overweight or having diabetes—but it may depend on the sort of bacteria churning around in the gut, a new study shows.

After reviewing numerous studies, scientists at Cornell University concluded “there is mounting evidence that gut microbiota composition affects obesity and diabetes, as does exposure to environmental chemicals” and that individual variations in gut microbiota may affect the way those chemicals are metabolized in the body.

The research is reported online in the journal Environmental Health Perspectives.

Current estimates suggest that the costs associated with obesity alone exceed $160 billion annually and account for more than 16 percent of medical care costs in the United States.

Gut microbes outnumber human cells by a factor of 10, yet little is known about many of them. The microbes serve a variety of functions, many related to weight and insulin control, including energy harvesting, regulation of fat storage, inflammation, and satiety. The most dramatic demonstration of this in people has come from gastric bypass surgery, which rapidly alters gut ecology and improves glycemic control in type II diabetics.

More than three dozen environmental chemicals have been found to be “obesogenic” or “diabetogenic”—affecting pathways leading to obesity and/or diabetes.

Some researchers believe these chemicals may act during critical windows of development around puberty to alter pathways involved in obesity.

Suzanne Snedeker, visiting fellow in the department of food science and Anthony Hay, associate professor of microbiology, have highlighted research, showing, for example, that pubertal exposure to tributyltin—used in anti-fouling marine paints as well as in some wallpaper, textiles, and floor coverings—caused weight gain and higher levels of insulin in the blood of male mice.

Several persistent pollutants like the insecticide DDT, dioxin, and PCBs have been identified in the human epidemiological literature as likely culprits affecting type II diabetes risk. Globally, high levels of arsenic in water supplies also have been associated with increased incidence of type II diabetes.

Snedeker and Hay note a dearth of research on the effects of gut microbes on environmental chemicals.

Gut microbes, however, can affect the metabolism of such over-the-counter drugs as acetaminophen and some chemotherapy drugs, making them more toxic. They conclude that a similar mechanism probably applies to chemicals implicated in obesity and diabetes and say further studies to determine exactly how are needed.

The researchers hope that new scientific approaches involving transplantation of gut microbes from humans into laboratory animals will lead to personalized treatments for diabetes and obesity and will help stem global epidemics.

The project received support from the David R. Atkinson Center for a Sustainable Future.

More news from Cornell University: www.news.cornell.edu

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