The use of antibiotics in young children might lead to a higher risk of obesity, and two new studies, one on mice and one on humans, conclude that changes of the intestinal bacteria caused by antibiotics could be responsible.

Taken together, the New York University researchers conclude that it might be necessary to broaden our concept of the causes of obesity and urge more caution in using antibiotics. Both studies focus on the early age, because that is when obesity begins, the scientists say.

The first study, published Wednesday in Nature, used mice to investigate the effects of low doses of antibiotic treatment. The researchers, led by Martin Blaser, thereby mimicked the treatment farm animals have been receiving in the United States in recent decades. Since the 1950s, low doses of antibiotics have been widely used as growth promoters in animals, reportedly increasing their size of by up to 10 percent.

‘People used antibiotics to treat infections, but then they were surprised that even in the absence of disease, this led to bigger animals,