We now know that the overuse of antibiotics has led to a rise in drug-resistant “superbugs,” but now there may be another reason to ease up on our use of the medications: they might be making us fatter.
Scientists learned during the development of penicillin that the antibiotic’s byproducts caused weight gain in animals. This knowledge makes up the partial logic behind the unhealthy science of feeding antibiotics to livestock to “beef them up.” New research shows that antibiotics have a similar effect on humans, as well. According to researchers from Johns Hopkins Bloomberg School of Public Health, kids who take antibiotics throughout their childhood gain weight “significantly” faster than children who don’t. 
The American Heart Association (AHA) says the prevalence of obesity in children more than tripled from 1971-2011. As a result, these youngsters are at increased risk for a variety of health problems in adulthood, including Type 2 diabetes, high blood pressure, and high cholesterol levels. Additionally, overweight children are often bullied and have low self-esteem. It seems the very drugs we give our kids to perceivably make them healthy are making them ill in the long-term.
“Your BMI may be forever altered by the antibiotics you take as a child,” said Dr. Brian S. Schwartz, a professor in the Department of Environmental Health Sciences at the Bloomberg School, in a statement. “Our data suggest that every time we give an antibiotic to kids, they gain weight faster over time.” 
For the largest study on the topic to date, Dr. Schwartz and his colleagues analyzed the health records of more than 160,000 children age 3-18 from 2001-2012. The team collected data on the youngsters’ height and weight to ascertain body mass index (BMI), in addition to the children’s antibiotic use in the previous year and any earlier years for which health records were available.
The scientists found that at age 15, children who had taken antibiotics 7 or more times during childhood weighed approximately 3 pounds more than children who had never taken the drugs. About 21% of the young study participants – over 30,000 children – had taken antibiotics 7 or more times during their childhood. 
Dr. Schwartz believes the findings actually underestimate the weight gain caused by exposure to antibiotics. He explained that is because his team lacked the health records for participants throughout their entire childhood, and that their findings were further hampered by the fact that the effects of certain antibiotic types were even stronger than the overall average.
“Our models suggest that the effect likely continues into adulthood and the BMI trajectories of children who did and did not receive antibiotics are increasingly diverging at older ages,” Dr. Schwartz told CBS News. “Although we did not observe children past 18 years, I would bet that this kind of pattern would continue.”
How, exactly, do antibiotics affect weight?
In addition to destroying “bad” bacteria, antibiotics also destroy “good” bacteria that are essential for a healthy gut. Scientists theorize that when we repeatedly take antibiotics, their byproducts dramatically impact our microbiome, forever changing the way it breaks down food and increases the calories of nutrients we absorb.
“Not only did antibiotics contribute to weight gain at all ages,” Dr. Schwartz warns, “but the contribution of antibiotics to weight gain gets stronger as you get older.”
The results of a study of nearly 10,000 Danish schoolchildren published in July revealed that pregnant mothers who used antibiotics had a higher risk of having a child who would become overweight or obese.
And since researchers warned in January that 10 million people a year will die by 2050 as a result of antibiotic-resistant bacteria, we would be smart to break our reliance on the drugs and research other natural antibiotic solutions. 
“Systematic antibiotics should be avoided except when strongly indicated,” Dr. Schwartz explains. “From everything we are learning, it is more important than ever for physicians to be the gatekeepers and keep their young patients from getting drugs that not only won’t help them but may hurt them in the long run.”
Parents should only agree to give their children antibiotics to treat bacterial infections, never viral ones.
“Bottom line: If your doctor tells you that you or your child does not need antibiotics, don’t ask for them, don’t take them, don’t try to find another doctor who will provide them. Eat healthy and your gut microbiota will be very good to you. Don’t change your gut microbiota unnecessarily by taking antibiotics if you don’t need them,” Dr. Schwartz advises.
The study appears in the International Journal of Obesity.
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Julie Fidler is a freelance writer, legal blogger, and the author of Adventures in Holy Matrimony: For Better or the Absolute Worst. She lives in Pennsylvania with her husband and two ridiculously spoiled cats. She occasionally pontificates on her blog.