The Connection Between Antibiotics And Weight Gain Explained

Shortly after antibiotics began to be mass-produced in the 1940s, farmers realized that adding them to livestock feed not only helped the animals survive better in overcrowded conditions but fattened them up faster. For a meat industry that is paid per pound instead of per animal, continuing the use of antibiotics in livestock feed for healthy animals seemed like a no-brainer. And as the demand for meat grew, so did the use of antibiotics (via Mother Jones). These days, approximately 70% of the antibiotics used to fight infection in humans are used in the meat industry, according to Scientific American.

However, growing evidence shows unintended negative consequences that include not only increased antibiotic resistance to certain diseases but weight gain that extends far beyond animals to include humans, too. Could widespread antibiotic use actually be increasing our waistlines?

Lee Riley, chair of the division of infectious diseases and vaccinology at the University of California, Berkeley, told The Atlantic, "We're animals, just like food animals. We give them antibiotics so they get fat. We are exposed to those antibiotics. It seems like a very common sense idea."

Antibiotics, we know, are designed to kill off certain bacteria that make us sick. But it seems they don't discriminate very well. As they destroy disease-causing microbes, they also kill off many "good" bacteria that our bodies need for essential functions, including the regulation of appetite. That leaves a significant imbalance in the gut microbiome — the many bacteria and other microorganisms that populate the gastrointestinal (GI) tract.

Pat Salber, physician and founder of The Doctor Weighs In, told Byrdie, "We now know that antibiotics have important effects on the billions of bacteria that live in the gut, including the guts of humans. And we know that these bacteria, collectively known as the microbiome, have significant effects on energy homeostasis and control of weight."

In fact, research has shown that lean and healthy people have a very diverse population of gut bacteria, while those who are obese host only a few dominant types of bacteria in their guts. While the causes of weight gain are complex and varied, the evidence between antibiotic use and weight gain is strong and growing.