In a last-ditch attempt to restore balance to her intestinal flora, her doctors recommended a fecal transplant, the technical term for the vogue medical procedure that is simply putting one person’s feces into another person. The idea is that the transplanted feces will populate the sick person’s bowels with a healthy bacterial population. At the request of the patient, the Newport doctors did not use a “professional” stool donor, but instead utilized the excreta of the woman’s 16-year-old daughter.

The transplant was a success, in that the woman’s symptoms went away. The bacterial ecosystem finally appeared to be restored to some kind of order. But they also seemed to have brought something else along. The woman’s daughter was obese, and in the months after the transplant, the patient gained 34 pounds, qualifying her as obese for the first time in her life.

“This case serves as a note of caution,” her gastroenterologists later wrote a medical-journal report. “We recommend selecting non-overweight [fecal] donors.”

Of course, many things could have caused her weight gain. Treatment of Helicobacter pylori, the bacteria that causes most ulcers, is itself associated with weight gain. Infectious-disease specialists at Massachusetts General Hospital Elizabeth Hohmann and Ana Weil noted at the time that “it is possible and perhaps even likely that the weight gain in the case reported was influenced not only by microbial communities transmitted during [fecal transplant], but also by genetic factors.”

In a randomized controlled trial of the reverse scenario, where overweight people with metabolic syndrome underwent fecal transplants from lean donors, recipients showed improvement in their degrees of insulin resistance. Taken together with other research on the effects of gut microbes on body weight and metabolism, Hohmann and Weill concluded in the same journal: “These studies take the concept of ‘you are what you eat’ to breathtaking new heights and certainly should stimulate further study!”

Of course, most people who are overweight have not had a fecal transplant. Most people will never need a fecal transplant. But the idea that a person can essentially contract obesity because of a change in gut microbes is at once exciting and unnerving—because exposure to microbe-altering drugs in day-to-day life has become almost inevitable. This month, the U.S. Food and Drug Administration quietly released a report that said over the past year, antibiotics sold annually for use in food animals increased to 33,860,000 pounds.

That’s a 22 percent increase since five years prior (which was the first time the amount was even measured). Usage also increased in 2014 alone, despite several prominent food producers and restaurants like Whole Foods and Chipotle swearing off antibiotic-raised animal products. Most of those antibiotics are “medically important,” meaning they are used in humans to treat diseases. But a majority of antibiotics are not absorbed by the animal, just excreted. So even those that are not medically important manage to find their ways into soil and water as they become part of the 18 gallons of manure that every cow produces every day.