posted on behalf of Nicola Jones
Farmers have long known that feeding low levels of antibiotics to their animals helps to beef up their beef. The drugs aren’t used just to keep diseases at bay – they also kill off normal gut bacteria that help to metabolize fats, leading to bigger pigs and cows.
This makes microbiologist Martin Blaser of New York University wonder if the same thing might be happening to people. Could overuse of antibiotics be one cause of the obesity epidemic in the United States? “I think this is what we’re doing to our kids,” he says.
“The average child in the United States gets 15 courses of antibiotics in the first 15 years of life,” he told the International Human Microbiome Congress in Vancouver, Canada, on 10 March. “That’s the average. And it’s all on the assumption that there are no long-term effects.”
Blaser is using mouse models to test his theory. So far he has reproduced the farming effect; low-levels of antibiotics (lower than would be used to treat disease) can boost mouse fat by 40%. When combined with a high fat diet, he says, he can get boosts of up to 300%. The group now aims to test antibiotic regimes more relevant to humans — pulses of higher doses, rather than chronic, low levels.
Obesity is a growing problem in the United States and elsewhere. Though sugary drinks, junk food, and lack of exercise are surely partly to blame, Blaser says gut microbes (or a lack of them) might play a big role too. Dusko Ehrlich, co-ordinator of the Metagenomics of the Human Intestinal Tract (MetaHIT) project in Europe, says that idea seems to fit with what his group is finding about obesity. MetaHIT has found that a class of obese people with 30% fewer gut microbes tends to put on more weight over time. “We couldn’t believe it,” he says of the radically depleted microbe numbers. What’s causing the microbial depletion? They don’t know. But antibiotic use, says Ehrlich, is a definite possibility.