There have been studies of the effect of fecal transplants on patient’s weight. I don’t know of any that have concluded that they cause rapid and permanent weight gain. There are a number of factors that contribute to weight gain... the number one factor is whether you eat more calories you burn off with your metabolism and activity level.
I don’t doubt that some people who are being treated for constant diarrhea and other digestive issues gain weight after their condition is successfully treated. When they can comfortably eat more food without pooping it back out immediately this would seem to make sense. And there probably are other possibilities as well. In the case you are referring to the “donor” was the woman’s own 16 year old obese daughter. But one case does not really prove anything. There were no controls and there are many factors that could contribute to unexpected outcomes.
“The average BMI of the patients before the transplants was 28.9, according to the study. When the BMIs were measured one to three months after the transplants, that average had decreased to 27.4, the researchers found. And generally, the patients who had BMIs that were higher than the average before the transplant showed greater decreases, according to the study.”
“the number one factor is whether you eat more calories you burn off with your metabolism and activity level.”
All things equal, sure.
The microbiome of individuals is not equal in species of bacteria nor concentration of population of species.
Apparently, some obese people have bacteria that increase obesity,
A fascinating area of study