The use of antibiotics to fatten up livestock may be partly responsible for an obesity epidemic in humans. Researchers in the United States have discovered a link between prophylactic, subtherapeutic antibiotic use and child development, leading to obesity.

In two studies released this week, researchers showed that low doses of antibiotics may alter children’s’ metabolisms and upset the balance of gut bacteria, leading to obesity. 

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In many parts of the world, antibiotics are used as growth promoters. The drugs have been fed to farm animals since the 1950s; whilst the practice is illegal in the EU, it is still widely used in the United States. Although tentative steps are being taken to challenge this, the United States’ meat industry lobby, which carries a lot of weight, has fought tenaciously to preserve subtherapeutic antibiotic use (that which serves merely to increase weight).

In the United States, an estimated 80 per cent of antibiotics used are on farm animals. The use of drugs to increase weight gain is widespread in cattle, swine, sheep, chickens and turkey, among other farm animals.

Ilseung Cho, who led a study at the New York University School of Medicine, the results of which were released on Wednesday in scientific journal Nature, found that antibiotics present in animal products as a result of subtherapeutic use affected the ‘gut microbiome,’ or stomach bacteria. Cho and his colleagues conducted tests on mice and concluded that, “By using antibiotics, we found we can actually manipulate the population of bacteria and alter how they metabolize certain nutrients. Ultimately, we were able to affect body composition and development in young mice by changing their gut microbiome through this exposure.”

Professor Frederick King, chair of the Department of Medicine at NYU Langone Medical Center, elaborated on the implications of the study, “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.”

In another study, released on Tuesday (21st August), body weight in children was found to rise in sync with their exposure to antibiotics as infants. Microbiologist Martin Blaser, also of New York University, who worked with Dr Cho on his study, found that at certain times young children’s weight was affected by antibiotic use.

Balser found that, on average, children exposed to antibiotics from birth to 5 months of age weighed more for their height than children who weren’t exposed. Between the ages of 10 to 20 months, this translated into small increases in body mass percentile, even factoring in the impacts of diet, physical activity, and parental obesity. By 38 months of age, exposed children had a 22 per cent greater likelihood of being overweight. However, the timing of exposure mattered; children exposed from 6 months to 14 months did not have significantly higher body mass than children who did not receive antibiotics in that same time period.

Dr Jan Blustein, who worked on the childhood obesity study, commented, “For many years now farmers have known that antibiotics are great at producing heavier cows for market. While we need more research to confirm our findings, this carefully conducted study suggests that antibiotics influence weight gain in humans, and especially children too.”

NYU’s Dr. Cho stated the scientific community is only just beginning to understand the complexity of the microbiome and how its effect on health and disease. He said his study has the potential to increase understanding of a wide array of conditions ranging from childhood obesity to metabolic syndrome in adults. He said more research is needed to study the effects in detail.

In the United States, the average child takes approximately one antibiotic course per year. However, there is growing concern in the medical community that antibiotic exposure may have long-term consequences, including effects on development and the potential for microbes to develop resistance to drugs. It is thought that subtheraputic and prophylactic antibiotic use exacerbate these issues.

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