BRISTOL — Maybe it started on that family vacation to the Azores a couple years back. With his stomach, hips and thighs wedged into the airplane seat, George Sousa could not latch one end of the seat belt to the other. He asked a flight attendant to bring him one of those embarrassing belt extensions.

Maybe it started one of those nights the family went out for pizza or pasta. When the hostess offered a booth, they’d decline. Mr. Sousa could not fit in a booth.

Maybe it started in his living room, on the couch, as he ate ice cream and watched NBC’s reality TV hit, “The Biggest Loser.” He’d watch the stories of obese people fighting their demons and get emotional.

Or maybe it was when they put his mother, Dorothy, in the ground, when a heart attack ended her life in December of 2007.

Maybe it was all of it — the throbbing knee pain, the sore feet, the lousy nights of sleep, the XXXL shirts, the restaurant booths, the TV tears, that embarrassing flight and mom’s funeral.

One day Mr. Sousa flipped a switch— in his psyche, in his personality, in his behavior, in his work ethic, in his everything — and decided enough was enough. He was 54 years old, stood 6 feet tall, weighed 340 pounds, popped six high-blood-pressure pills per day and had never worked out a day in his life. Never played sports. Never worried about what he ate. Never joined a gym.

One day he changed his entire life.

Mr. Sousa walked into a gym, an instructor showed him how to use the machines, gave him a rough plan of what to do and then let him go. Mr. Sousa did the rest.

He started working out daily at Bristol Total Fitness. In those early days, he’d survive three minutes on the elliptical machine before stopping, his chest heaving.

He signed up for a nutrition program, learned what to eat, what not to eat, how to read food labels, how to cook vegetables. He learned the dangers of sodium and fat, of potatoes and pasta, of his favorite chourico sandwiches.

Like a rubber ball hurled against a brick wall, he turned his entire life around and bounced back the other way, and the way he describes it, it was just that simple.

“One day I decided I had to change ... Maybe it was my mom’s heart attack. I said, ‘if I don’t lose this weight, I won’t make it to retirement.’ ”

As he spoke, he was relaxing in his living room. He wore black, swishy athletic pants — the kind you wear to the gym and then peel off for your workout — sneakers and a loose T-shirt. His goatee was gray and tightly cropped, his head the same. He looked like a high school gym teacher, one of the nice ones.

Today Mr. Sousa is a fitness nut. He works out six days a week. Monday to Friday, he’s there at 5 a.m. He does his own workout, some days weights, some days cardio, before he showers, changes and leaves before half the world has hit the snooze button.

On Tuesdays and Thursdays, he’s back at the gym for an evening spin class (it’s like an aerobics class on stationary bikes). On Saturdays, he’s there again for spin class.

He’s now 55, and at his latest weigh-in he was 236 pounds — 104 pounds lighter than a year ago. He takes only two blood pressure pills per day.

His knees don’t ache much anymore, his feet don’t hurt and he sleeps soundly at night. He can spend an hour on the elliptical machine, and he hasn’t eaten a slice of pizza in more than a year. He might be the only American who can say that.

George Sousa is a different man. People who have known him for 20 years barely recognize him. It happens all the time. He bumps into people in the supermarket — he’s a regular in the organic foods section — at the pharmacy, in restaurants, at his grandson’s high school wrestling matches.

No one can believe the transformation, and regardless of how many times he hears it, he never tires of it. “It’s a nice, nice feeling,” he said.

Two decades overweight

George Sousa was born in Bristol and has lived his whole life there. He graduated from Bristol High School, Class of 1972. He and his first wife had three children together, Michael, Greg and Carrie. The marriage didn’t last, and Mr. Sousa got re-married 28 years ago. At that time, he was already a heavy guy. Overweight was the only way his wife, Jane, knew him.

“Until the past year, my wife had never bought me an extra-large shirt before. She always had to go to different stores to get me triple-XL,” Mr. Sousa said.

His father, Harold, who’s 80 and lives on the other side of the duplex house they own, watched as his son grew over the years. And grew and grew. The elder Mr. Sousa is thrilled at what his son’s done in the past year.

“He really did it all himself,” said Harold Sousa. When the son reached the pinnacle of his climb — 100 pounds shed — the gym celebrated with a testament on its wall, including before and after photos. The father took a copy for himself. “I was so proud of him,” he said. “I showed that to everyone.”

Student becomes a teacher

The younger Mr. Sousa has done more than turn only his life around. He’s pulling others along with him. He convinced his 80-year-old father to join the gym, too. Dad now walks on a treadmill four or five times a week. Mr. Sousa’s brother-in-law is working out now. So are other family members.

His wife is a fit woman who doesn’t need to lose weight, so while she hasn’t joined him at the gym, she’s joined him at the kitchen table. The hidden side of Mr. Sousa’s remarkable transformation is his diet. Few people besides those closest to him realize how completely he changed.

He eats no sweets of any kind. No French fries. No mashed potatoes. No baked potatoes. No whipped potatoes. Sweet potatoes, yes, but all other potatoes, no. No pasta, unless it’s whole wheat, and then only sparingly. Of course no more pizza, calzones or chourico sandwiches.

All of this comes from his work with Emily Gedney of Evolution Bodywork and Nutrition. Ms Gedney, a registered dietitian, taught Mr. Sousa everything she could about eating healthy, and he devoured her lessons. He’s now religiously devoted to healthy foods.

It also helps that he’s an incredible creature of routine. He eats the same breakfast, snack and lunch every day. Breakfast is a slice of organic bread toasted with organic peanut butter, a hard-boiled egg and two cups of coffee, sugar, no cream. Snack is another hard-boiled egg and a banana. Lunch is Boar’s Head low-sodium turkey with low-fat mayonnaise on pita bread, an apple, banana and water.

He spices things up at dinner, cooking different combinations of chicken, fish or turkey with vegetables and low-starch sides like brown rice. He records all of it, daily, in a journal.

None of this has been easy. That kind of diet demands discipline and will power. It also costs a lot. Even though he may be eating less than he did a year ago, Mr. Sousa is spending more. Bananas, broccoli and Brussel sprouts are a lot more expensive than hot dogs and French fries. Organic foods can cost 50 percent more than regular foods.

“It costs a lot more to eat healthy,” Mr. Sousa said.

He has no desire to stop, however.

“I feel so much better,” he said. “I have more energy. I sleep more soundly. I can walk up stairs and not get winded … so much better.”

Ms. Gedney, the dietitian, said Mr. Sousa is one of the most successful clients she’s ever worked with, and she does not measure success by numbers on a scale. Success is measured in a person’s well-being. “The few who really get it, look at food as fuel for the body, and they take the whole emotional attachment out of it,” Ms. Gedney said.

Mr. Sousa has done that, which is why he can eat the same breakfast, snack and lunch every single day, and why he hasn’t had a slice of pizza in more than a year. “He could have pizza if he wanted to,” said Ms. Gedney, “he just doesn’t.”

Even though she’s immersed in a field that pushes people down healthy paths, Ms. Gedney is amazed at the road Mr. Sousa traveled. “When I first met him, he was so shy, his self-esteem was low ... Now he’s so much more confident, his attitude is awesome. What he’s done is just remarkable.”

Life begins at 100

By October of this past year, Mr. Sousa was almost to his goal of losing 100 pounds when life slammed back at him. Five minutes before the end of a shift at the Reed-Rico manufacturing plant in Bristol, he was told that was his last day. The company was making a small round of layoffs and his job was gone.

It’s devastating news to anyone, and had it happened to Mr. Sousa a year earlier, it might have been an overwhelming setback. Instead he channeled it. He worked out angry for a few weeks, and then he moved on.

He won a $5,200 grant from the Rhode Island Department of Labor and Training to cover the entire cost of tractor trailer driving school. He’s five weeks into a 10-week program to earn his Class A license at the Teamsters Local 251 driving school in East Providence, and he’s optimistic there will be a job waiting for him to drive big rigs when he gets out.

This story isn’t over. Mr. Sousa believes he could lose a few more pounds. Friends want him to try a road race. He’s still teaching his loved ones about healthy eating.

And temptation always looms. There are more pizza joints in Bristol than in any place this side of Federal Hill. Summer barbecues, family get-togethers, holiday parties — any one could knock him off track.

But it would have to knock hard. George Sousa is a different man today. He hit the wall already and he’s moving in a new direction.