Corporate Japan will join the country's battle against bulging waistlines next month with the introduction of compulsory "flab checks" for the over-40s and penalties for firms that fail to bring their employees' weight under control.

Health authorities hope the measures will arrest the rise in obesity among middle-aged men and slow soaring medical costs. All employees over 40 - about 56 million people - will be required to take the test to determine whether they are at risk of metabolic syndrome - symptoms associated with being overweight that, if left unchecked, increase the risk of strokes, heart disease and diabetes. Men with girths of more than 85cm (33.5in) will be given exercise and diet plans and, in urgent cases, told to see a doctor.

The health ministry estimates that 13 million Japanese suffer from metabolic syndrome, while another 14 million are at risk. Men are about 10% fatter than they were a decade ago, while women are more than 6% heavier. The ministry hopes to see a 25% reduction in the number of people at risk over three years.

According to reports, firms will be required to cut the number of overweight workers and their dependants by 10% by 2012. Those that fail to reach the targets face surcharges of up to 10% on contributions to a welfare fund for the elderly.

"If it can prevent even a small number of people from developing cardiovascular diseases it will be good news for them and their families," Yuji Matsuzawa, director of the Japan Society for the Study of Obesity, wrote in the Asahi newspaper.