How did the study establish causality? Basically, how did they determine that obese people lose the “gut-brain” reward connection, as opposed to people who lack

How did the study establish causality? Basically, how did they determine that obese people lose the “gut-brain” reward connection, as opposed to people who lack the connection being the ones who become obese in the first place? The fact that this connection isn’t regained after weight loss would suggest that it was the genetic lack of this connection that led the participants to become obese, as opposed to obesity causing them to lose this connection.