Most of us would say that obesity is a consequence of eating too much, exercising too little, and an unfortunate combination of genes, but things might not be so simple. A new study suggests that the microbes in our gut can influence how we put on weight, and because these organisms can move from one person to another, it might be possible to literally 'catch' obesity from others.
For the first time, scientists in the UK have shown that a third of the spores produced by bacteria in the human gut can survive out in the open air. This implies that the people we come into close contact with could influence our own gut bacteria as these spores spread through the air.
That's not to say that if an obese person sneezes on you, your weight is going to balloon, but many previous studies have shown a link between the make-up of our gut bacteria and our weight. If these bacteria can exist outside the body as the new research shows, then our own internal ecosystem could be affected by our closest friends and family.
To be clear, the study doesn't say these spores are definitely jumping from person to person, just that they have the potential to, and that's definitely worth a closer investigation.
Superbugs such as Clostridium difficile spread in this exact same way. "I think there are definitely diseases that are caused by an imbalance in microbiotia," lead researcher Trevor Lawley from the Wellcome Trust Sanger Institute told Sarah Knapton at The Telegraph. "If you look at something like inflammatory bowel disease. Or obesity, that’s a possibility."
"People who live in the same house share a similar microbiome," added Lawley. "And genetics only really accounts for between 7 and 13 percent of the risk. There are definitely people who are more susceptible to disease and so it could be a combination of things."
One hypothesis put forward by the new study is that some diseases tend to run in families because they share living spaces, rather than because of anything at the genetic level. It's still early days for this research, though, so consider the idea of contagious obesity an intriguing possibility for the time being.
Lawley and his team managed to grow over 130 types of gut bacteria in lab conditions for the purposes of their studies. They're hoping that by analysing them outside of the body, they can develop drugs to treat various kinds of illnesses fostered by the gut - drugs that could eventually replace faecal transplants, perhaps.
"By developing a new process to isolate gastrointestinal bacteria, we were able to sequence their genomes to understand more about their biology," said one of the team, Hilary Browne, in a press release. "We can also store them for long periods of time making them available for further research."
We're only just beginning to understand the relationship between our internal microbiomes and obesity, though, and a good diet and plenty of exercise remain crucial. A study from 2013 showed that when mice were fed an unhealthy diet, it prevented healthy, 'lean' types of bacteria from flourishing, so be sure to look after the little guys in your gut.
The group's work has been published in Nature.