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Breath Test Reveals Gut Bacteria Linked To Obesity

A growing body of evidence is increasingly showing us that the microbes in our gut influence our metabolism in surprising ways. Now a new study from the US suggests that a breath test of the gases they give out may indicate how susceptible a person is to developing obesity.

In The Endocrine Society's Journal of Clinical Endocrinology & Metabolism 26 March online issue, researchers from the Cedars-Sinai Medical Center in Los Angeles report how people with high levels of both hydrogen and methane in their breath are more likely to have a higher body mass index (BMI) and a higher proportion of body fat.

They suggest the presence of certain bacteria in the gut causes it to extract more calories from food, adding to weight gain.

Lead author Ruchi Mathur, director of the Diabetes Outpatient Treatment and Education Center in the Division of Endocrinology at Cedars-Sinai, says in a statement:

"This is the first large-scale human study to show an association between gas production and body weight," adding that "this could prove to be another important factor in understanding one of the many causes of obesity."

Mathur and her colleagues tested the exhaled breath of 792 people and found four patterns: normal breath, or breath containing higher levels of methane, higher levels of hydrogen, or higher levels of both gases.

And the participants' whose breath had higher levels of both methane and hydrogen were the ones significantly more likely to have a higher BMI and higher proportions of body fat.

A gut bacterium called Methanobrevibacter smithii is responsible for most of the methane produced in the human gut.

Mathur says that usually bacteria like M. smithii are beneficial because they help extract energy and nutrients from food.

But if there is too much M. smithii, it alters the energy balance so as to make the person more likely to put on weight.

It does not do this directly, but by the effect it has on neighbouring bacteria, the researchers suggest.

M. smithii produces methane by scavenging hydrogen from other microrganisms. The researchers propose that this gives hydrogen- producing bacteria a boost, making them more efficient so as to extract more nutrients and calories from food. It is this, which eventually leads to weight gain, says Mathur.

Mathur is also working on another study that seeks to confirm the link between M. smithii, obesity and pre-diabetes. On that study the participants are given a dose of antibiotics to wipe out the bacterium so that researchers can compare how efficiently they digest food when they have the bacterium in their gut to when they do not.

Mathur says we are only "beginning to understand the incredibly complex communities that live inside of us".

"If we can understand how they affect our metabolism, we may be able to work with these microscopic communities to positively impact our health," she adds.

Several examples of the surprising ways gut bacteria influence the human body have emerged in recent years.

For instance, an animal study published in the Journal of Proteome Research in February 2012, suggests that gut bacteria may play a role in obesity by slowing down the activity of energy-burning brown fat.

And in a study published in February 2013, US scientists describe how gut bacteria form part of a complex system that maintains the body's blood pressure.

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