Antibiotic-Laced Meat: Making Us Fat? 'Mother Jones' takes a look at recent studies By Evann Gastaldo, Newser Staff Posted Jan 2, 2013 1:04 PM CST 22 comments Comments (Shutterstock) (Newser) – Animals on factory farms are given antibiotics because the drugs have been shown to fatten them up for slaughter—which raises the question, do antibiotics also cause weight gain in humans? And what about the fact that many of us eat these factory-farmed animals—will that make us fat? Mother Jones looks at a number of recent studies addressing those questions: Why do antibiotics cause animals to gain weight? They cause small changes to the "gut microbiome," the billions of microbes living in the digestive tract. And the different composition of microbiota also leads to an increase in fat mass, because gut microbes are involved in breaking down carbs. Antibiotics allow the microbes to break down more carbs, thus converting them to more fat. What about us? Yep, antibiotics appear to have a similar effect on humans, at least for a while. Researchers found that in a study of more than 11,000 kids, those who were exposed to antibiotics as babies had a 22% higher chance of being overweight, but that effect wore off by age 7. And about that antibiotic-laced meat? The FDA does impose limits on how much antibiotic residue can be in meat meant for public consumption, but one expert says we don't really know enough about the subject, and the meat we eat could very well be messing with our gut flora. At least one study has shown that even small levels of antibiotics can affect microorganisms.