Having a friend, sibling or spouse who is overweight raises a person's risk of being obese too, US researchers say.
They said data on more than 12,000 people suggested the risk was increased by 57% if a friend was obese, by 40% if a sibling was and 37% if a spouse was.
They argued this showed social factors, such as the body sizes of other people, were important in developing obesity.
Experts said the New England Journal of Medicine study was not conclusive as other hidden factors could be to blame. Researchers at Harvard Medical School and the University of California, in San Diego, looked at data collected over 32 years as part of a heart study.
Participants gave personal information, including their body mass index, and the names of friends who could be contacted.
The authors were able to map social connections including both friends and family members.
The effects were generally larger between people of the same sex.
And their analysis suggested that the links could not be solely attributed to similarities in lifestyle and environment, for example the impact of friends existed even where friends lived in different regions.
Source - BBC