Farmers who feed their livestock antibiotics to fatten them up could be contributing to human obesity, according to new US research.
Since the 1950s, low dose antibiotics have been used as growth promoters in the agricultural industry to make cattle, pigs, sheep, chicken and turkey gain weight.
Now researchers believe that when we eat meat treated with the antibiotics, it reacts with our gut bacteria affecting our metabolism.
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Dr Ilseung Cho from the New York University School of Medicine led a team of researchers who administered antibiotics commonly used to fatten livestock to mice. Over six weeks, the mice gained 10 to 15 percent fat mass and had a change in hormones related to metabolism.
"By using antibiotics, we found we can actually manipulate the population of bacteria and alter how they metabolise certain nutrients," Dr Cho said in a media release.
"Ultimately, we were able to affect body composition and development in young mice by changing their gut microbiome through this exposure."
Over recent years, scientists have been concerned about the increasing use of antibiotics and how they affect human development. The concern is that we are absorbing antibiotics through meat and experiencing weight gain as a result.
"This work shows the importance of the early life microbiome in conditions like obesity," said lead investigator Martin J. Blaser from the NYU Langone Medical Center.
"The rise of obesity around the world is coincident with widespread antibiotic use, and our studies provide an experimental linkage. It is possible that early exposure to antibiotics primes children for obesity later in life."
Using antibiotics as growth agents in livestock is now banned in Europe, but is still allowed in Australia and the US.
Professor Joseph Proietta from the University of Melbourne told ninemsn this study adds to evidence that our gut bacteria can impact our weight.
"In our large bowel we have trillions of bacteria — these bugs digest food and, although all the mechanisms aren't known, it's clear that the type of bugs in our bowel can influence our weight," he said.
But Professor Prioetta said we need more research into how antibiotics from livestock could affect human gut bacteria.
"We need a lot more research in this area but the bugs in the bowel are important," he said.
"The authorities will need to look at this now."
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Professor Prioetta said the research highlights the need for medical practitioners to be responsible when administering antibiotics.
"It warns us about a possible consequence of antibiotics in meat that we didn't think about before," he said.
"We shouldn't be taking antibiotics unnecessarily — but of course if we need them, we have to have them."