Farmers have long used antibiotics to cows, pigs and turkeys faster weight gain. Now scientists claim that antibiotics given early in life can also make children grow fat. The researchers believe that drugs alter the composition of the bacterial population in the gut in a crucial stage of development that can have a long term impact.
Other scientists cast doubt on the findings, however. The new data is "unconvincing" said Michael Blaut, a microbiologist at the German Institute of Human Nutrition in Potsdam, Germany. And David Relman, a microbiologist at Stanford University School of Medicine in Palo Alto, California, called "provocative" work, but said some of the data are "a bit vague and unclear."
The billion microbial cells live in the guts of humans and other animals. research into these large bacterial populations, called microbiomes, is only beginning, but scientists already know that some microbial residents play a crucial role in the degradation nutrients in our diet. Some also believed that antibiotics at low doses given to farm animals to make them grow bigger, might work by altering the intestinal microbiome.
to test this hypothesis, team led by microbiologist Martin Blaser of New York University School of Medicine in New York added antibiotics mice drinking water that had just been weaned. The drug-either penicillin, vancomycin, a combination of both, or chlortetracycline-was administered at doses comparable to those approved by the US Food and Drug Administration as growth promoters in farm animals. After 7 weeks, the group of mice on antibiotics had significantly more fat than a control group of ordinary drinking water, the team reports online today in Nature . "This confirms what farmers have shown for 60 years that low-dose antibiotics cause their animals grow," says Blaser.
If the results of the study are replicated in other animal models, such as pigs, they could have significant implications for public health, said Oluf Pedersen, genomic medicine professor at the Center of the Novo Nordisk Foundation for basic metabolic research at the University of Copenhagen.
the antibiotics do not reduce the total number of microbes in the guts of animals, but changed their composition. the DNA comparison showed that mice treated with antibiotics had a higher proportion of bacteria belonging to the group Firmicutes than in control animals. Firmicutes might be able to extract more calories from food and deliver them to the host, Blaser argues. The results are relevant to humans as well, he said. Another document Blaser co-authored, published online in the International Journal of Obesity yesterday reported a link between antibiotic use in infants and obesity in childhood .
The researchers studied data collected from more than 11,000 children born in Avon, UK, in 1991 and 1992. Those who had been treated with antibiotics in the first 6 months of life were more likely to be overweight at 10, 20 and 38 months of age. "There is an association, and it does not mean causality," says Leonardo Trasande, the first author of the paper. "But coupled with Nature paper, he began to tell a compelling story."
Blaser argues that his work shows that antibiotic use in babies has misunderstood cost. and while they are sometimes necessary, antibotics are often used willy-nilly, he said.
But others say caution is in order. in the human study, weight differences were small, and there was no correlation between the use of antibiotics in 6 first months and weight to 7 years, the last time information was collected on children. and there are many reasons why mouse experiments should not be extrapolated to humans and children, said Relman. the study was conducted with a single inbred mice. Seven weeks is a long time in mice, which ripen quickly and live for only 2 or 3 years, he said. "We never give antibiotics to children continuously from the time they wean when they reach sexual maturity."
In addition, differences in fat mass between mice and antibiotics fed controls are small, Blaut said. Relman and points out that if they got bigger, the total weight of the mouse has not increased, as occurs in farm animals. "Although it does not expect antibiotics to it to work the same in all species and in all circumstances, it seems odd that there was this effect and not gain weight," Relman wrote in an email.
Finally, Relman warns that the microbiome composition of the mice was measured only at the end of the experiment. "This means that we do not know if microbiome changes were the cause, the result of, or unrelated mouse fat content of change," he said. Blaser calls this a valid criticism, but adds that he began to address this issue. "We have shown in other experiments that are not even the transfer of the microbiome also transfers obesity mouse for the next published."
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