Gut bacteria, Obesity & Bad Breath

Lou Bowler Naturopath

Ever wondered what your breath really says about you? Well, according to some very recent research, the characteristics of a person’s breath may reveal how susceptible they are to gaining weight.

Analysing the breath of 792 participants (not a job I would like to do!), revealed that people who had high levels of hydrogen and methane gas are more likely to have an increased body mass and accumulation of body fat. The breath test results were classified into one of four different groups: those who had a normal breath content, those who exhaled higher concentrations of either methane or hydrogen, and the last group which had increased levels of both gases in their breath. This last group also tended to have higher body fat percentages and a higher body mass index (BMI).

woman holding her hand over her mouth

Could an imbalance in your gut flora (known as dysbiosis) be contributing to bad breath and weight gain?

According to the research, a person will exhale more hydrogen and methane gas if a microorganism known as Methanobrevibacter smithii (M. smithii for short) is abundant in their digestive systems. Previous research regarding M. smithii has found that this organism is the predominant methane-producing bacteria in the human digestive tract, and researchers have hypothesised that an overabundance of M.smithii could lead to increased body fat accumulation and overall weight gain. It appears that having an imbalance in gut flora which allows M. smithii to become the dominant organism, could contribute to obesity.

One of the characteristics of M. smithii is its ability to scavenge hydrogen from other gut microbes which it uses to produce methane. A current theory suggests that it is this interaction which helps other hydrogen-producing microorganisms extract nutrients from food more efficiently and which could thereby lead to weight gain and obesity through the extra absorption of calories. The study also found that M. smithii may also influence insulin signalling (a process which plays an important role in blood sugar regulation).

So in a nutshell, this research suggests that the types of bacteria in our gut might influence our weight - the more M. smithii you have (as measured by the concentration of hydrogen and methane on your breath), the greater your body mass index. This is not the first time we have reported on the possible link between gut microbiota characteristics and obesity. You can read more on this topic in this article: Do our gut bacteria play a part in metabolic conditions and obesity? 


  1. Mathur, R et al (2013)"Methane and Hydrogen Positivity on Breath Test is Associated with Greater Body Mass Index and Body Fat," Accepted for inclusion in the April 2013 issue of Journal of Clinical Endocrinology & Metabolism.
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