People dump things in Fitton Hill, Oldham, home to 12-year-old Ryan Owen. A sofa lies abandoned at the end of his street of small council houses, and further along a sagging armchair waits for someone to take a rest from life in this grinding suburb of one of Britain's most depressed towns. There's a sprinkling of litter, which features its fair share of the McDonald's wrappers you see all over the country. A brightly coloured cup from a Happy Meal shows Ronald McDonald kicking a football around, and urges the young diner to 'find a wide open space and kick a ball as far as you can!'

Ryan Owen is supposed to be doing just that, or something very similar, on this bright Sunday morning. Ryan weighs 16 stone and hasn't been to school since last November, saying the bullying about his weight is too bad for him to ever go back. His school, Breeze Hill comprehensive, has said they're not aware of any problem, but his case is bad enough for social workers and community leaders to have stepped in, gradually coaxing him back out into a world in which he's hardly the only fat child.

They've persuaded him to join a local walking group which meets three times a week to go for gentle walks around Oldham's green belt. Everyone else in the group is older the Ryan, their triple bypasses slowing them down in the same way that Ryan's extra bulk does him. This morning, though, Ryan has disappeared. The rest of the group is expecting him in the local Alexandra Park, as is his mother, Tracey Morris, who has just arrived with her other children, Zack, four, Hope, six and Emma, eight. She thinks Ryan might have gone to ride around on the buses, which he sometimes spends the day doing, or perhaps he's at an open day at the local police station.

Tracey isn't sure how he got like this. Her son started to eat more when he was about nine or 10 and has steadily put weight on ever since.

Now, his appetite is so huge that it takes two or three McDonald's burgers to fill him up, so she can't afford to bring her family there any more. She says she has £40 a week to spend on food for herself and her four children, an amount that gets you few Nectar points, and fewer still of the healthy, easy to assemble meals bought by svelte urbanites up and down the country.

There's still no sign of Ryan on the walk so we take a stroll around the park, Tracey pushing Zack in his buggy while Hope and Emma run around the food stalls that are part of the 'healthy food' fair that happens to be on today. Tracey refers to Emma as 'the skinny one', but Hope looks as if she might have a future like Ryan's ahead of her. They fill the pram and their pockets with free fruit, which they don't seem to mind eating. But when I ask Tracey where she usually gets her fresh fruit, she tells me the closest supermarket is Asda, two bus rides away. There is a minimarket close to her house, but there's a catch. 'Apples there are 25p each,' she says with the air of someone who knows exactly where every penny is at any given time.

At Asda, she can buy a bag of nine apples for 89p, or around half the price. Two bus rides seems a long way to go for an affordable apple, and Tracey's predicament backs up a claim in a recent Demos report that 'achieving a nutritious diet on a low income requires extraordinary levels of persistence, flexibility and awareness'. Picturing her trying to get the children, the buggy and her £40 worth of shopping across Oldham on the buses, it doesn't come as a great surprise to hear that she went to the doctor recently, saying she's stressed out. He gave her a course of antidepressants.

Tracey is making an effort, in her own way, and partly due to the fact that she's got a battle with her own weight on her hands. The family used to eat chips four times a week; now she's got it down to twice. People speak of Fitton Hill as being 'cut off' from the rest of Oldham and in just the same way, she and her kids are divorced from the foodie culture that permeates Britain. There are no dinner parties at her house, and Ryan never has friends around for tea. There is no poring over food labels for GM content or fat grams. Tracey considers the healthiest food of all to be pasta, something the rich and thin of this country are dropping like hot potatoes.

I go back to the house later, to see if Ryan has reappeared. He has, but one of his sisters apparently called him a 'fat boy' so he's locked himself in his room and won't come down. Tracey says eating when he's upset is one of Ryan's big problems, and that he'll binge on anything he can find when he's like this. He'll have to be out by Tuesday, though, when she takes him to the clinic to be weighed.

I go into Oldham to see what a 12-year-old boy who goes in there to ride on the buses might find. The high street is empty and chilly - a Dairy Milk wrapper blows across the road like tumbleweed, and the only places that look warm and open are McDonald's and Burger King. Among the incongruous number of jewellery shops, there's a shop advertising back-to-school stationery, 'as cheap as chips'.