London ? The English city of Manchester has come up with a simple formula it hopes will help keep its citizens trim: eat right, get stuff. Exercise, get more stuff.

Manchester is hoping to fight fat with a reward system that works like a retail loyalty card. But instead of earning credit for opening their wallets, residents will be rewarded for keeping their feet on the treadmill and their fridge stocked with healthy food.

Starting next fall, Manchester residents will be able to swipe their rewards cards and earn points every time they buy fruits and vegetables, use a community swimming pool, attend a medical screening or work out with a personal trainer. Points can be redeemed for athletic equipment, donations to school athletic departments and personal training sessions with local athletes.

The money is coming from the government’s health service and from local authorities.

“We’re not looking for customers to be loyal to a particular store, but to help people make healthier choices,” said Laura Roberts, the chief executive of Manchester’s National Health Service.

One public health official said the program seemed worth pursuing even if it is untested.

“I haven’t seen any evidence that it works, but that doesn’t mean we shouldn’t try it,” said Timothy Armstrong, coordinator of the World Health Organization’s global strategy on diet, physical activity and health. Armstrong said obesity was such a pressing issue that “as public health officials we really don’t have the luxury of waiting to see what works and what doesn’t.”

He said he was particularly impressed that Manchester, which has a population of 2.5 million, had managed to rope grocery stores, advertisers, fitness clubs and private companies into the plan.

“We really do know that, in terms of curbing the obesity epidemic, all of society needs to play a role,” he said.

Like other countries in the developed world, Britain is struggling to keep its citizens’ waistlines in check. Last year a government-commissioned report predicted that as many as nine out of 10 adults could be overweight by 2050, costing the country’s National Heath Service more than $78 billion a year.

Manchester’s program is modeled after the kind of reward programs run by major British grocery chains, such as Tesco and Sainsbury’s.