Rosette Kalayjian was worried.

Her dad had recently been diagnosed with a potentially fatal aortic aneurysm. Surgery had saved his life.

But she wasn’t sure what was going to save her husband’s life.

At 5-foot-11 and 345 pounds, Dr. Tro Kalayjian was big. Very big.

He knew better.

He was a doctor.

Rosette, pregnant with their third child, had always been accepting of her husband.

“(But) she turned to me, thinking out loud, (and asked), ‘The way you’re going, am I going to lose you?’ “ Kalayjian recalled.

That was Dec. 7, 2015; three years and 157 pounds ago.

“My wife really started this journey. I owe it to her,” said Kalayjian, 35.

The journey, which will include crossing the finish in Sunday’s Orangetown Recreation Santa Claus 5K Run, has seen Kalayjian reshape not just his life but also his career.

Kalayjian, the chief resident at a hospital in New Jersey three years ago, has since dedicated himself professionally to making others fit. By February or March, the Palisades resident will open a practice in Tappan.

And there’s humor in the site he has chosen.

“I wanted the formerly obese weight-loss doctor to change the previous chocolate store into a weight-loss practice,” he said.

Early heavy years

Kalayjian, who lost 80 pounds in a year without exercise by severely restricting his intake of carbohydrates and limiting the hours he ate, wasn’t a guy who’d never had a weight problem and suddenly found himself fat.

He was 5-foot-6 and 200 pounds at the start of high school. By the end, he was 5-10 and the same 200.

At 15, he decided to lose weight to help himself. And he decided to study medicine after high school to help his family. Many members were obese — some suffering from diabetes and high blood pressure.

He ran cross-country his senior year at Tappan Zee (class of 2001), and that, along with other exercise, helped keep his weight down. But he links his actual high school weight drop more to a diet he now scoffs at as unhealthy and unsustainable.

Kalayjian fasted for a month, then followed a super strict vegan diet.

“(I was) kind of anorexic,” he said

But after high school, he stopped exercising and returned to previous eating habits, which he defends to some extent as mirroring recommendations. He consumed oatmeal, rice, whole grains and lots of fruit.

He also did this around six times a day.

Kalayjian became pre-diabetic, had sleep apnea and low energy.

All of that is gone.

A big meat and fish eater, he has embraced exercise. After dropping 80 pounds, he started hitting the treadmill at Retro Fitness in Tappan.

“I started very slow, very easy. I got my body moving after I lost 80 pounds,” he said, laughing about binge-watching "The Walking Dead" while on the treadmill.

He “ramped it up” from there. He clocks five-minute miles and lifts weights.

And for the past couple of years, he has changed the lives of athletic and non-athletic patients — devout vegans to voracious carnivores.

He has treated patients online, advocating low carbs and restricted hours of food consumption.

Technology has allowed him to remotely monitor patients’ blood-sugar levels 24 hours a day. He can also track blood pressure, and a smart scale allows him to track body weight and patients’ percentage of body fat.

“Never in my career had I taken anyone off insulin prior to what I’ve done now. The cost of insulin is skyrocketing. I take at least one to two patients a week off now,” said Kalayjian, who plans to continue his online practice once he also opens his office.

While he doesn’t treat family members, he advises them. The results have been striking.

One brother has gone from 400 to 255 pounds. His other brother dropped 50 pounds. His mother lost 20 and is off one diabetes medication. His dad lost 30 and is off two blood-pressure medications.

And his wife — who wasn’t fat — lost 15 pounds almost “vicariously ... from me lowering my sugar and carbs,” he said.

Of his own progress, he said, “My joints don’t hurt. I’m not tired all the time.”

But Kalayjian may end up at least a little tired Sunday. He can’t remember the last time he ran a race.

But he recently ran the Santa Claus route, completing it in 20 minutes.

Still, he’d like to go faster.

“If I get 19:30 or lower, I’ll be super, super happy,” he said.

Kalayjian’s wife (a “saint,” who “loved me at 350 pounds and loves me now”) is already happy just seeing her husband healthy.

Their kids, Ari, 6; Aleen, 4; and Raffi, 2, see old pictures and say, “You were so big.”

Ari races his dad all the time and his dad, of course, lets him win.

On Sunday, Ari will do the shorter kids’ Santa Claus run.

That makes his dad smile, as did a question his son recently posed.

“He said, ‘Dad, can I go out and run 10 laps around the block?’ " Kalayjian said.

Family culture has changed: one bite — and one step — at a time.

Twitter: @HaggertyNancy