At a Phish concert four years ago, Tyler Whitman thought he might die. He weighed 400 pounds at the time, and, as he danced, he started to feel woozy.

“I couldn’t get through one song,” the 6-foot-tall 33-year-old tells The Post. “It was torture.”

He eventually fainted and fell to the ground. When he came to, he was embarrassed and humiliated.

“My friend David sat down next to me and I lost it. I sat there sobbing and told him, ‘I am so tired of being the fat guy.’ ”

That year, the struggling real estate agent decided to make a change: In December 2015, Whitman kicked off his health journey when he had part of his stomach removed in a gastric-sleeve operation at New York University.

Today, at a fit 185 pounds, Whitman’s gone from “the fat guy” to a thriving broker — and the newest cast member of Bravo’s “Million Dollar Listing New York,” which premieres Thursday.

“One of the [storylines on the show] is how weight loss has affected my career,” says Whitman.

The surgery was a major part of Whitman’s slim-down success, but it’s not the whole picture: There’s also his newfound passion for fitness and — deliciously — a diet consisting mostly of Chipotle. Whitman eats at the Mexican fast-casual chain twice a day — every day — and credits it with keeping his weight in check.

“[It] feels like a treat to me, and it’s still fully in line with my health goals,” says Whitman, who isn’t affiliated with the chain.

It took Whitman some time to discover that Chipotle’s burrito bowls were the key to staying slender. After his operation, he started on an all-liquid diet, slowly introducing solid food in limited quantities. “Half a sandwich felt like a holiday feast,” he says.

Five months after the surgery, he’d lost 100 pounds. But then he hit a plateau.

“I wasn’t skinny, I was just less fat,” says Whitman. Before the operation, he’d led a sedentary life. If he wanted to lose more weight, he realized, exercise would be key.

“All of the doctors I spoke to told me surgery would only get me part of the way there,” he says.

In the spring of 2016, he challenged himself to do 90 exercise classes in 90 days — and take a gym selfie every day to hold himself accountable.

By July of that year, he’d taken dozens of spin, yoga and Barry’s Bootcamp classes and reached his goal weight of 185 pounds.

Then came the biggest challenge for any dieter: actually keeping the weight off.

Now in a solid fitness routine, Whitman began to re-examine his nutrition. He turned to the Whole30, a restrictive diet that bans grains and processed foods. In the middle of this diet, he heard about the potential of healthy Chipotle bowl options.

“A friend tipped me off that if I was careful about ingredients, Chipotle was a great place to eat [Whole30] compliant meals on the go,” says Whitman.

So, for the past year, he’s eaten two 750-calorie chicken burrito bowls — one for lunch, another for dinner — every day. And he’s kept the weight off.

Whitman says his typical bowl includes: brown rice, fajita vegetables, chicken, mild and medium salsas, sour cream, guacamole and lettuce.

“I genuinely think it’s delicious,” says Whitman, who passes on cheese, beans, tortillas and chips, and orders a “light” portion of the rice and sour cream. He’s been working to build more lean muscle, so he asks for extra chicken. For snacks, he has two 190-calorie s’mores flavor Quest bars per day.

It’s an unorthodox meal plan, but it “gets me within my calorie and protein goals, and that’s all I count,” says the broker. “I eat 2,000 calories and 180 grams of protein, and everything else works itself out.”

Doesn’t he ever get bored?

Nope. “I’m a creature of habit and convenience,” says Whitman, who typically frequents the burrito chain’s Ninth Avenue and 44th Street location, which is near his Triplemint real estate brokerage office.

He currently works out six days per week, sometimes with a trainer. He’s in a relationship with another health fiend who “also loves Chipotle,” which is helpful for staying on track.

The real estate broker says he’s transformed his wallet as well as his body. Before his weight loss, Whitman recalls not being taken seriously by high-end buyers and didn’t feel happy or confident in the business. After reaching his goal, “the floodgates opened.” He’s now a partner at Triplemint and works on properties selling in the $2-million-to-$4-million range. “The commission is lovely.”

He recently splurged on a pair of Cartier sunglasses and says “fashion” — not food — “is my new addiction.”

This Labor Day weekend, he’s going to Denver to see Phish, where he expects to remain conscious the entire time. Despite his professional success, he’ll be traveling in coach.

“When I was obese, I was too overweight to fly economy. So I would fly first class because I felt too shameful buying two seats — and this is when I had no money.” Now, the jam-band fanatic says, “I have plenty of money, but I’ll only fly economy because it’s such a source of pride.”

It’s been a challenging journey, but Whitman believes that his personal struggle with weight has made it easier to connect with buyers.

“Moving is a big emotional deal,” he says. “There is usually a life story connected with the purchase of a home, and I really dive in.”

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