Bulging babies: 3 or more antibiotics before age 2 may spur obesity

For decades, farmers have known that the quickest way to fatten up young, healthy livestock is to feed them antibiotics—the drugs will even plump animals on a diet. It’s unclear why the practice, called growth promotion, works. Scientists have a range of hypotheses, including that the drugs may kill off gut microbes that compete for calories or knock back mild infections that would otherwise take energy to fight off. Whatever the answer, one thing is certain: growth promotion spurs drug-resistance in bacteria. And with the rise of infections from such superbugs in people—a major threat to public health—the practice is now squarely discouraged.

Yet, despite the long-held practice in farms, researchers are just beginning to harvest data on whether the drugs have the same effect on human babies in clinics. So far, much of the data—but not all—shows some concerning similarities.

Looking at a population-representative sample of nearly 22,000 children in the United Kingdom, researchers found that giving children three or more courses of antibiotics within the first two years of life modestly increased the likelihood that they would be obese at age four. The study, being published in Gastroenterology, follows several smaller studies that hinted at such a connection, particularly for antibiotics used in the first six months of life.

“Collectively, we’re starting to recognize that maybe there’s more to avoiding antibiotics than just the antibiotic resistance problem,” gastroenterologist Frank Scott, of the University of Colorado-Denver, told Ars. “No doubt that that’s probably the biggest issue facing us right now,” he added. Still, Scott said it’s important to look at these subtler, potentially life-long health effects.

Past studies looking into this issue found similar effects on weight gain in childhood and beyond, but these often relied on parents' recall of how many antibiotics their children took, used much smaller pools of kids, or showed mixed results. Scott and colleagues set out to conduct a cleaner, larger study that relied on comprehensive electronic medical records that followed kids for years.

Of the 21,714 children with complete records in the study, about 64 percent were given antibiotics in the first two years of life. The researchers then adjusted the data for factors known to influence childhood obesity, including maternal and sibling obesity, maternal diabetes, mode of delivery (C-section, for example), socioeconomic status, year and country of birth, and urban dwelling.