Gastric bypass surgery is remarkably effective at promoting weight-loss (it cuts the long-term risk of early death from morbid obesity by 40%), and it's long been presumed that the major action by which it worked was that, by bypassing the parts of the gut where most food absorbtion takes place, it limited the calories that subjects' bodies could harvest from the food they ate.
An NIH-funded study published this week in Nature's journal of the International Society for Microbial Ecology (Sci-Hub mirror), researchers find that most (and possibly all) of the weight-loss can be attributed to a better, more diverse gut microbiome following the surgery, which they attribute to a reduction in gut acidity, which makes the gut more hospitable to bacteria that are associated with weight-loss.
The study involved fewer than 100 subjects, and will need replication at scale, obviously.
That means if you could find another way to make the gut a happy home for these waste-trimming microbes, you could get the same outcome without the dangers of surgery.
"My vision is to figure out a way to first treat the gut to create the right environment to for this microbiome to establish itself," says Krajmalnik-Brown. "The end goal is to come up with a probiotic that can be used to enhance weight loss instead of surgery, because surgery is risky." Only about 1 in 1,000 people who go in for bariatric surgery don't make it out, but the more obese you are the more dangerous it is to go under the knife at all.
Obesity Surgery May Work by Remaking Your Gut Microbiome [Megan Molteni/Wired]
Distinctive microbiomes and metabolites linked with
weight loss after gastric bypass, but not gastric
banding [Zehra Esra Ilhan1, John K DiBaise, Nancy G Isern, David W Hoyt, Andrew K Marcus, Dae-Wook Kang, Michael D Crowell, Bruce E Rittmann and Rosa Krajmalnik-Brown/International Society for Microbial Ecology] [Sci-Hub mirror]