ScienceDaily (Aug. 22, 2012) — Researchers at NYU School of Medicine have made a novel discovery that could have widespread clinical implications, potentially affecting everything from nutrient metabolism to obesity in children. Since the 1950's, low dose antibiotics have been widely used as growth promoters in the agricultural industry. For decades, livestock growers have employed subtherapeutic antibiotic therapy (STAT), not to fight infection or disease, but to increase weight gain in cattle, swine, sheep, chickens and turkey, among other farm animals. First author Ilseung Cho, MD, MS, and colleagues set out to reveal how antibiotics were acting on the body to create this effect, hypothesizing that low doses of the drugs may alter the composition and function of the bacteria in the gut. The resulting study, appearing August 22 online ahead of print in Nature, confirmed their theory about the gut microbiome, the term used to refer to the community of bacteria that lives in the stomach, and raises new questions about how manipulating it can impact metabolism and disease in the body. The researchers administered STAT to normal mice and observed that the mice receiving antibiotics developed increased fat mass and percent body fat. After about six weeks, the mice that received antibiotics had gained about 10 to 15 percent more fat mass than the mice that did not receive antibiotics. The researchers also noted that bone density was significantly increased in STAT mice early in development and that particular hormones related to metabolism were affected by antibiotic exposure, as well. "By using antibiotics, we found we can actually manipulate the population of bacteria and alter how they metabolize certain nutrients," said Dr. Cho, assistant professor of medicine and associate program director for the Division of Gastroenterology at the School of Medicine. "Ultimately, we were able to affect body composition and development in young mice by changing their gut microbiome through this exposure." Full article http://www.sciencedaily.com/releases/2012/08/120822130837.htm Also this from BBC News: Antibiotics can make young children heavier, says study Giving antibiotics to young babies may increase their weight later in life, according to US researchers. A study of 11,532 infants, published in the International Journal of Obesity, showed children under six months who were given antibiotics were heavier in later years. Researchers say the drugs could be affecting bacteria in the gut, leading to weight changes. However, they say more work is needed to confirm there is a link. Bacteria living on people greatly outnumber the body's own cells and there is a growing interest in how this "microbiome" affects human health. In extreme circumstances there are even examples of doctors transplanting faecal matter in order to introduce healthy bacteria into the gut, treating infections when other methods have failed. In this study, children who had antibiotics between birth and the age of five months were slightly heavier between the age of 10 and 20 months. After 38 months they were 22% more likely to be overweight. One of the researchers, Dr Leonardo Trasande from New York University School of Medicine, said: "We typically consider obesity an epidemic grounded in unhealthy diet and exercise, yet increasingly studies suggest it's more complicated. "Microbes in our intestines may play critical roles in how we absorb calories, and exposure to antibiotics, especially early in life, may kill off healthy bacteria that influence how we absorb nutrients into our bodies, and would otherwise keep us lean." Microbiologist Dr Cormac Gahan, from University College Cork, said there was certainly a lot of interest in the area, "but it is very early stages for this type of work". He said changing gut bacteria could alter weight by "a direct effect on energy extraction" or by "influencing hormones".