The human gastrointestinal tract is a complex environment that is populated by different types of microorganisms, including bacteria. There is growing evidence to suggest that these microorganisms play an important role in various physical processes. Researchers recently discovered another microscopic lifeform in the gastrointestinal tract that belongs to the archaea family, also known as ancient bacteria. These single-celled organisms usually tend to occur under extreme circumstances, such as heat, cold or high pressure. Methanobrevibacter smithii, or M. smithii, is an ancient bacteria that is commonly found in the gastrointestinal tract. The presence of this bacteria has recently been linked to obesity.

The researchers examined the faecal samples of nearly five hundred children aged six to ten for the presence of this bacteria. They found that the bacteria was present to some degree in eighty percent of the children, with twenty percent showing no signs of the bacteria at all. The researchers then tracked the children's height and weight over the course of several years. According to Ilja Arts, professor of Molecular Epidemiology of Chronic Diseases, they found a surprising link. 'The higher the concentration of M. smithii, the greater the risk of developing obesity. In larger concentrations, the risk could be three times as high.' The researchers were unable to explain why the presence of M. smithii increased the risk of obesity.

'They do know that M. smithii and other bacteria in the gut play a role in the digestion of dietary fibres that cannot be broken down by the body,' says Arts. Having established a clear link to obesity, Arts recommends conducting additional research on the role of ancient bacteria. 'We suspect that obesity is more than just the result of eating too much and exercising too little. Other factors, such as microorganisms in the gastrointestinal tract, likely play a role as well. They may also contribute to obesity-related complications. Some obese people develop cardiovascular disease or diabetes, while others don't. We want to know why.' Arts believes that a better understanding of microscopic colonisation in the gut could lead to more targeted interventions, such as individual dietary advice.

These results were part of the KOALA study and were recently published in the scientific journal Obesity. The study was conducted as part of the public-private partnership TI Food and Nutrition.