Scientists at Harvard University say the dramatic rise in adult obesity over recent decades is due, in large measure, to its spread through social networks - including family, friends, co-workers and neighbours.

And the issue doesn't stop there: the findings also suggest that the more obese people we know, the greater our chances of gaining weight.

Joe Moore, president of The International Health, Racquet & Sportsclub Association (IHRSA), said: "Our collective complacency about the impact that sedentary lifestyles and poor food choices have on our health must end.

"If each of us acts, both individually and together, we can break the social cycle of obesity."