Treating infants with antibiotics may predispose them to being overweight later in childhood according to an article published in August 2012 in the International Journal of Obesity. When treated in the first 5 months of life, the risk among 10,000 infants of being overweight was 22% higher than those not treated with antibiotics. The type of microbes living in our gut play a major role in how we digest food, absorb its nutrients, and keep out toxins.
It is possible that antibiotic treatment would alter the gut microflora in such a way that it could lead to being overweight.