How Boyz II Men's Nathan Morris Lost Over 30 Lbs. and Toned Up: 'I Had to Commit Or Quit'

Losing weight isn’t easy, especially if you have a schedule like Nathan Morris does.

As a founding member of the iconic R&B music group Boyz II Men, Morris’ busy career includes a residency at The Mirage in Las Vegas and a new album, Under the Streetlight, debuting in the fall.

So, when Morris, 46, decided to lose weight, he knew he’d have to seriously commit to a healthy lifestyle to stay on track.

“It just struck me one day,” he tells PEOPLE. “I’ve tried many times but was never able to keep the weight off until realized it couldn’t just be a diet. I had to “commit or quit” as I say.”

Morris “completely changed” how he ate and made fitness “a must.”

“On Sept. 26, 2016, I started my workouts weighing 249 lbs.,” he says. “I was able to get my overall weight down to 208 lbs. in fat loss and then was able to add 10 to 12 lbs. of muscle.”

Morris recently took to Instagram to show off his body transformation, posting a photo of himself onstage lifting up his shirt to reveal six-pack abs. He also shared how he reached his goal, which included removing sugar, starches, dairy and most carbs from his diet.

“I cut out all carbohydrates except the good ones,” says Morris, who now opts for brown rice and yams. “I stick to lots of green vegetables, good proteins, lots of water and a good supply of vitamins.”

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To get that toned physique, Morris says: “I stopped doing cardio for hours and instead replaced it with 15 to 20 sprint intervals – walk for three minutes, sprint as fast as you can for 30 seconds to one and a half minutes. I do that off and on till I reach 15 or 20 minutes. Then I do some resistance training, either with weights or with the TRX straps.”

As for his fitness philosophy? “I focus not on how much weight or how many reps, but more on good form and slow speed lifting to create more time under tension. That’s what makes your muscle grow strong,” says the musician. “As my good friend [and Boyz II Men trainer] Tony Cress says, ‘The more time you can keep the muscle under tension, the more you get out of the workout even if it’s on 6 reps instead of 12.'”

And his body transformation has helped keep his energy up during performances as well.

“I feel great!” he says. “Like anyone, there are those days that you just don’t want to get up and do it, but that’s when it really counts. That’s your mind trying to trick you and once you get moving, it all goes away.”