The 13th week on the road was the hardest so far for Steve Vaught, a 180-kilogram man trying to walk across America.

On the Sunday morning, he found a creek just as the desert heat forced a midday break. But when he woke from a nap and tried to fill his water bottles, the stream had already gone dry. Late that night, he accidentally walked right past his scheduled motel stop in Truxton, a flyspeck on historic Route 66 so slight it vanished when the sun went down.

On the Monday, out of water in 39-degree Celsius heat and kilometers from any town, he sent a frantic text message to his wife, who called the local police. They drove him to a hotel, where he rested a night and a day, sick with dehydration. On the Wednesday he started late and tangled with a scary dude on the desolate highway.

"I'm quitting,'' he told his wife. She said OK.

But within hours he hit the road again, as they always knew he would. For quitting is not so easy when you're 800km from home.

Three weeks later, he is still going strong and on Tuesday was on his way to Winslow, Arizona.

This spring, as he neared his 40th birthday, Vaught had an epiphany: If he didn't lose weight, he would die before he hit 50. But dieting would not work, he decided, and neither would normal exercise. He knew he was the kind of guy who could rationalize his way out of one five-km walk after another.

"My weakness,'' he said, "is the easy way out.'' So Vaught made it hard. On April 10, he left his San Diego home - and his wife and two children - and started walking, alone, to New York.

There's something about the United States geography that inspires this kind of journey: To hike the Appalachian Trail, to kayak the entire Mississippi River, to drive from Maine to Key West, and maybe make sense of things along the way. Which is how it has gone for Vaught, on the road mulling issues far beyond weight or willpower.

The trip has not gone completely as planned. He has only rarely come even close to the pace of 30km a day he estimated would put him in verdant Missouri by now, not arid Arizona in July. He strained a couple of ligaments shortly after he started, and he lost three toenails climbing the final mountain pass out of California.

"Does this seem insane?'' Vaught wants to know. He is a big guy, 1.85 meters, a former Marine and longtime towtruck operator who, as the fat melts away from his cheekbones and jaws, is beginning to bear a slight resemblance to the buffed-up actor Jerry O'Connell, but with a lumberjack beard and shock of hair like an unmowed lawn.

Well, that depends on what you mean by "insane.'' Doctors, certainly, would call it inadvisable. A seriously overweight person embarking on any kind of strenuous physical activity could dangerously stress his joints and heart, says Samuel Klein, director of the Center for Human Nutrition at Wash-ington University in St Louis.

And such activity is especially worrying in an area of environmental extremes, without someone to support him, Klein says. Even if Vaught weighed 45kg, "walking across a desert without someone standing next to him with an umbrella and a fan and Gatorade might really be a problem.''

Vaught, meanwhile, has been almost completely on his own. For the first few days after he set off from the Pacific Ocean, his wife, April, would pick him at up the end of the day to bring him home to sleep at her mother's house, where the family is staying. Soon, though, he had gone far enough that he had to start camping. He hasn't seen his family in six weeks.

Now and then a friend catches up with him for a few hours or days. But mostly it is just him and his 35kg pack.

Since entering the desert, he has had to cut back his walking hours dramatically. Now he walks from about 5.30 to 8.30 in the morning, when he finds shelter - preferably in a store or post office if one is around, but usually under a bridge or in a culvert or bush.

He'll sit there for 11 or 12 hours until it's cool enough to walk again for a few hours.

Vaught accepts a ride from a reporter 55km down the road to a public library, where he checks his e-mail.

There is one from a 37-year-old guy preparing to run his first marathon. A 62-year-old woman planning to hike the Pacific Crest Trail. People in such places as St Louis and Altoona, Penn-sylvania offering food and water and a place to stay when he comes their way. Overweight people nationwide begging to know Vaught's daily distance so they can match it at home.

Only a few call him crazy. Almost all say what an inspiration he is.

It is something to think about, on those lonely and terrible days on the road, he says.

"Now I have all these people not to let down,'' he explains.

Even at 185kg he never thought of himself as a fat guy. Perhaps because he never used to be, perhaps because it was the least of his problems.

Fifteen years ago, he was the fun guy. A slew of girlfriends, a bunch of friends, a witty streak so hot he would gladly take the stage at a comedy club open-mike night. Then one evening in Oct-ober 1990, driving too fast against the setting sun, he struck and killed an elderly couple crossing the street.

The accident sent him to jail for 10 days, ruined him financially and dulled him emotionally. When he put on the weight, he just didn't care. He remembers little about the next three years.

After the birth of April's first child, he grudgingly went to therapy, just so April would know she had done everything she could in case he killed himself.

Medication snapped him out of his depression. But life didn't get any easier. A few businesses failed and they went deep into debt on a house. And the weight, he realized, was bringing him down.

"There's nothing appealing about fat people,'' he says bluntly. "You can't impress them when you're fat.''

His jobs steadily declined in quality. In March he said he walked away from the latest, managing a muffler repair shop, after the owners sniped about him sitting down too much at work.

One morning that week, he turned to April in bed. "I ought to walk across the US,'' he said. Once he left, he added, it would be hard for him to quit.

"If that's what it's going to take,'' she replied.

So he has a lot to think about as he walks. About the anger he carried around for so long and how pointless it seems now. About how accepting help from people doesn't shame him any more, now that he sometimes has to ask strangers for water. And about the value of living in the moment, of just sur-viving that next stretch of road.

"It has nothing to do with weight any more,'' he says. "It's about getting back to the person I was.''

Vaught gets the reporter to drive him back to the outskirts of Peach Springs, near where he stopped walking. At 5pm, it's still 33 degrees C, and he looks for a place in the shade where he can wait.

He sees it about 45 meters off the highway, a culvert over a now-abandoned part of the original Route 66.

"This is good,'' he says. He lifts his pack on to his shoulders. The strap holding it to his still massive gut now has 20 centimeters of excess past the buckle, compared with 5cm when he began.

He manages to heave his body over the guardrail and starts walking. By the time the car has turned around and driven past again, his 160kg have vanished into the desert.

For daily updates, see www.thefatmanwalking.com

THE WASHINGTON POST