Gastric bypass surgery is generally considered one of the most effective weight loss strategies for morbidly obese people, but a new study suggests there could be more to its success than just restricting your portion size.
Around 15,000 people undergo weight loss surgery -- including gastric bypass -- every year in Australia.
It is a drastic procedure generally only used after other weight loss attempts have failed, yet gastric bypass is becoming more and more common in the face of our obesity crisis. It involves an operation to staple off a large section of the stomach, reducing it to a tiny pouch and so forcing the patient to cut down their portion sizes.
But researchers from Arizona State University say the procedure is having another, previously overlooked effect: it's dramatically changing the make-up of the obese person's gut bacteria. And these changes are likely helping the person continue to loss weight after the surgery.
The surprising findings could pave the way for effective new weight loss treatments without the dangers and life-changing restrictions of bariatric surgery.
The past year has seen huge advances in our understanding of the gut microbiome -- the population of tiny bacteria living in our guts which help us digest food. Disruptions in the microbiome have been linked to everything from depression and psychiatric conditions through to sleep and migraines.
One of those findings was that obese people have less diverse gut microbiomes. This is generally thought to be due, at least in part, to junk food diets starving the good bacteria in our guts.
The Arizona University researchers likened gut diversity to a fragile democracy, where a diverse microbial network provides checks and balances. If diversity falls, then certain bacteria such as salmonella may take over and tyranny prevails, with disastrous effects for the individual's health.
In this latest study, the scientists analysed the diversity of the gut microbiomes and waste products of 24 obese people who had undergone gastric bypass surgery, and compared them to normal-weight individuals, other obese individuals who hadn't had surgery and some who'd undergone lap-band surgery -- another, less drastic form of bariatric surgery.
The researchers found that obese people who had undergone gastric bypass surgery had a high level of diversity of gut bacteria -- even more diverse than healthy-weight individuals.
Moreover, these changes appeared to be permanent.
The lap-band surgery -- where an adjustable silicone belt tightens the stomach, effectively reducing its size -- did not produce a similar effect.
This suggests that the actual removal of part of the stomach and small intestine was what prompted the greater diversity, the researchers say. They believe the surgery disrupted the gut so much that bacteria previously unable to survive in the obese gut was able to flourish.
"You're giving new microbes a chance to make it," lead author of the study, Zehra Esra Ilhan, explained.
"Most of the species are acid sensitive, which supports the idea that changes in stomach pH levels may permit these microbes to survive and make it to the colon."
Gastric bypass surgery has high rates of success in helping morbidly obese people lose weight and keep it off, with most individuals losing between one-third and two-thirds of their excess weight, as well as drastically reducing their rates of type two diabetes and sleep apnea.
But the surgery is not without risks.
As well as the initial dangers of the procedure, patients may have difficulty getting enough nutrients -- including vitamins, protein, iron and calcium -- because part of the stomach and the upper section of the small intestine are bypassed.
This reduces the number of calories absorbed by the body, causing them to lose weight, but it also means that less nutrients are absorbed. People who have had bariatric surgery generally need to take supplements every day for the rest of their life.
The researchers hope their discovery will help pave the way for microbial transplants -- where healthy, diverse bacteria is transplanted into an obese person's gut -- without the need for drastic and irreversible surgery.
In a 2013 study done on mice, microbes from obese mice who had undergone a gastric bypass were transplanted into obese mice who hadn't had surgery. The obese mice who hadn't had surgery lost almost 30 percent of their excess weight and kept it off.
"A probiotic that would replace surgery would be great," Ilhan said.
"Another positive outcome would be if we can find a microbial biomarker that will identify the best candidates for surgery and sustained weight loss."
The results of the study were published in the scientific journal, the International Society for Microbial Ecology (ISME).
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