George Sinclair was alone at home, drinking “cheap, pour-it-down-the-sink stuff,” when he realized he needed to change his lifestyle. He was 25 years old and weighed 304 pounds.

He couldn’t climb a flight of stairs without breaking a sweat, and his body kept forcing itself to the front of his mind, each time he had an itch and couldn’t reach it, each time he felt hot when everyone else was cold, each time he sat down and noticed his stomach before him.

“When you’re that size,” he says, “You never stop thinking about it.”

On January 2, Sinclair—who lives in the U.K.—took his first step toward a new way of living. Now, nine-and-a-half months later, he's down 122 pounds. In a recent interview with Men's Health, Sinclair revealed the keys to his transformation.

With help from the smartphone app MyFitnessPal, he set out some simple rules for himself: Exercise a little every day; cut out fatty and sugary foods; and focus more on “useful stuff” like chicken and lean proteins. The foods he enjoyed, like pizza, were still game, but with limitations.

“I’ll see people try to stick to an extreme, like eating a carrot every night for dinner,” he says. “That’s not fun. I just try to moderate what I eat. I love pizza, and now I don’t go very much, but when I do, it tastes even better.”

For fitness, Sinclair started by walking. He’d hike to his job at the London, England, transport system, or walk to the shops on weekends. When he felt fit enough for it, he began running each day.

On Saturdays he’d go to group runs at his local park, and on his days off he’d drive out to the London countryside and find different trails and routes through the hills and woods. Sinclair never bought a gym membership, and he never lifted a weight. Instead of being bored by the cardio, he was energized by it.

“Running was never something I was able to do, but my whole body feels recharged every time," he says. "My legs feel good, my airways feel good; it’s easy to breathe. I feel cleansed, on top of the world.”

It’s a far cry from where he was at the beginning of the year, when Sinclair says he was “barely passing” his required medicals at work and potentially on the verge of innumerable health crises.

“I took a cold look at where I’d be in 10 years, and it wasn’t anywhere good," he says. "I didn’t have diabetes…yet. I didn’t have high cholesterol…yet. I hadn’t had a heart attack…yet. Now I feel like I’m going away from those things instead of toward those things.”

Sinclair has two pieces of advice for other guys looking to make a change. One: Don’t be sunk by the setbacks. Sinclair had a couple “half-ass attempts” at losing weight in the past, but when those programs didn’t provide immediate results, he abandoned them entirely instead of persisting.

Two: Find the courage to take that first step. Sinclair’s greatest challenge was looking in the mirror and recognizing his need to make a change, but he found the motivation to break through.

“I felt like I was on an edge with one foot hanging over," he says. "Sometimes you have to take that step to just do it.

“You look at stories like this and it seems like weight loss was something that happens to other people, but weight loss doesn’t ‘happen’ to anybody. You do it. You have to be the change.”

Sinclair’s 30-Minute Cardio Playlist

Notice Sinclair’s t-shirt in his transformation picture? Not an accident. “I used to be a really obnoxious Iron Maiden fan," he says, laughing. "I had long hair, the shirt, Iron Maiden shoes, an Iron Maiden wallet. I was in the fan club, had the pins, knew all their songs on bass. I mellowed out a few years ago, but I still love the band.”

Here, Sinclair shares the five Iron Maiden songs that will drive you through an intense half-hour of cardio:

1. “Run to the Hills”This is your starter, thanks to a “really good build up and a killer drum intro.”

2. “The Trooper”Picking up the pace? This is a faster track. Sinclair recommends matching your speed to the tempo of the bass.

3. “Loneliness of the Long Distance Runner”You’re in the heart of your run now. Power on with this aptly-titled no-brainer.

4. “The Prisoner”Time to switch things up. Sinclair recommends this song for intervals: “Jog for the lower tempo, sprint like crazy for the higher tempo.”

5. “When The Wild Wind Blows”Cool down with this steady 11-minute track. When it’s done, you’re done. “It has a steady, strong beat that’ll keep you in the mood,” Sinclair says.