Men put on more than a stone in weight between 1986 and 2000, scientists at Oxford University have shown.
According to the research, which is published in the British Journal of Nutrition, the average man was 7.7kg heavier in 2000 than he was in 1986.
The trend is thought to be due to a combination of increased calorie intake and reduced physical activity.
While the average man ate enough food in the year 2000 to make him 4.7kg heavier than his forebears in 1986, the fact that the actual difference in weight was 7.7kg shows that the problem was not down to diet alone.
Lead researcher Dr Peter Scarborough said: 'One partial explanation could be that men spend more of their working lives sitting at desks now - manual careers are less common than they used to be.'
He warned: 'This research suggests a ticking time bomb for male health, and underlines the importance of both regular exercise and a balanced diet in keeping your weight down and your heart healthy.'
Recent figures from the NHS Information Centre confirmed that the prevalence of obesity has indeed been rising among men in England.
Almost a quarter of adult males (24 per cent) were obese in 2008, compared to just 13 per cent in 1993, according to the latest report.