IN 40 years 40 per cent of the US population will be obese, according to a new prediction based on American trends.

Alison Hill’s team at Harvard University developed a statistical model to predict the spread of behaviours through a social network of friends, family and neighbours, together with those behaviours that spontaneously arise without social influence.

The researchers applied their model to data taken over the last 40 years on the spread of obesity in 7500 people living in Boston.

Two per cent of the population became obese each year, with a person’s chance of becoming obese increasing by 0.5 per cent for each contact they had with an obese person. Taking into account recovery rates from obesity and extrapolating to the wider population, Hill’s model predicts obesity levels will plateau in about 40 years, at which time 42 per cent of Americans will be obese.

The prevalence of obesity in the Boston group has historically tracked closely with US levels, so the findings could indeed be valid nationwide, says Hill (PLoS Computational Biology, DOI: 10.1371/journal.pcbi.1000968).