People who find success in a wellness programme are more influential in getting friends to sign up than a charismatic but less successful person, the findings showed.
"Your ties and social contacts may have a bigger effect because you see them every day and you have that close connection," said Lora Cavuoto from the University of Buffalo.
"If they can be successful, then that's your best way of getting information out that a programme is good and it works," Cavuoto added.
Among peers people in social networks linked to someone who successfully lost weight produced the largest total weight-loss based on the simulations.
Networks surrounding people with a high number of charismatic or popular friends produced lower weight-loss totals.
The findings could help diet and exercise programmers reach more people by advising marketers on which people to target as endorsers.