Farmers may have fuelled the human obesity epidemic by using antibiotics to increase daily liveweight gains in livestock, a new study claims.

Although the use of antibiotics to raise animal performance is now banned in the EU, their use is still permitted in countries such as the USA where more than one third of adults are obese.

The study, carried out by New York University, showed antibiotic use could alter the fine balance of bacteria in the gut, altering the body’s metabolic function and leading to weight gain.

Martin Blaser, who led the study, said findings demonstrated how early exposure to antibiotics could “prime children for obesity later in life”.

As part of the research, common antibiotics such as penicillin and vancomycin were administered to weaning mice at similar doses as that used in agriculture.

After about six weeks the mice had gained about 10-15% more fat mass than untreated mice.

“Indiscriminate use of antibiotics for livestock (often used to fatten animals), not only promotes the spread of antibiotic resistance, but can get in our food chain and affect the homeostasis of our gut microflora.”
Brendan Wren, London School of Hygiene and Tropical Medicine

Co-author Ilseung Cho, also from New York University, explained: “Ultimately, we were able to affect body composition and development in young mice by changing their gut microbiome through this exposure.”

Although it was known that antibiotics could fatten up animals, previously the mechanism involved was unclear.

As reported in the Irish Times, British expert Brendan Wren, from the London School of Hygiene and Tropical Medicine, said: “The role of the composition of our gut microflora is increasingly recognised as being important and has been linked to inflammatory bowel disease, metabolic disorders, immunity and obesity.

“It has been considered as the forgotten super organ in humans, and it is only now through advances in genome sequencing that we can assess the composition of the complex population of microbes in the gut.

“Indiscriminate use of antibiotics for livestock (often used to fatten animals), not only promotes the spread of antibiotic resistance, but can get in our food chain and affect the homeostasis of our gut microflora.”

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