Obesity treatment could be required by more than one person in any social group of friends of family.
This is because the problem tends to be 'transmitted' between people who spend a lot of time together.
It has previously been assumed that shared ideas about an acceptable body weight and size are responsible for this phenomenon.
However, recent research published in the American Journal of Public Health and conducted by a team from Arizona State University has confirmed that this concept only has a small role to play.
While monitoring 101 women and 812 of their closest family and friends, the researchers found no evidence to support the idea that people feel some pressure from their peers to achieve an ideal body size even when they might not agree with this view themselves.
The concept of people changing their diet and exercise to fit what they had learned was an acceptable body size is from friends was also dismissed.
Meanwhile, the proposal that individuals tend to form an appropriate body size simply from observing the bodies around them was only given minimal support.
As a result of these findings, the authors suggested that the reasons behind shared obesity could be more focused on the fact that people exercise and eat together.