Walter Fisher was on a heater.

Gambling lingo for a lucky streak, a “heater” is a run of unbridled fortune. From February until June 2016, the 36-year-old poker professional couldn’t lose.

“I hit the zone and just felt it,” he says. “I ran two grand up to $97,000 at blackjack. I put up big numbers at poker.”

He accrued a six-figure windfall and the ride seemed endless — until it wasn’t. “I got overwhelmed and began playing over my head,” Fisher says.

It took less than a month for Fisher to lose it all — and gain between 40 and 50 pounds. He was more than $100,000 in debt, and as his bankroll contracted, his waistline expanded. “I ordered double veal parms to the poker table; I ate full pizzas,” says Fisher, a Forest Hills native, who ignored friends’ suggestions to slow down. “I’d lose a bundle at blackjack and eat three or four superrich single-serving chocolate cakes. They had to have [had] more than 1,000 calories each. It was disastrous.”

At 6-foot-1, Fisher tipped the scales at 245 pounds, and his spiraling financial losses showed no sign of abating. “I was broke, big and isolated. People dream of what I had accomplished, and I lost control,” he says.

In December, an opportunistic gambling acquaintance offered to bet Fisher $100,000 that he could not reduce his body fat to less than 10 percent in six months. Desperate and hungry for change, Fisher booked the bet, tapping two high-stakes friends, Dan Bilzerian (the famous Instagram playboy) and Bill Perkins (a wealthy hedge fund manager who plays poker), for backing.

Before the month was out, more than $1 million in wagers had been lined up. The money was secured in an escrow account; half of it, in excess of $500,000, was earmarked for Fisher if he could break the 10-percent body-fat mark. Winning would wipe out his debt and replenish his bankroll.

He started dieting and exercising but quickly realized he couldn’t do it alone. On Fisher’s behalf, a friend reached out to personal trainer Chris DiVecchio.

DiVecchio, the owner of Premier Mind & Body in Los Angeles, got involved for an upfront fee and a cut of the back end. Although Fisher thought his body fat was 25 percent when he made the bet, it actually measured 33 percent. Even worse, “he had no athletic ability or training,” says DiVecchio. “I had to get him sweating and comfortable with feeling sore as hell.”

Fisher began an intense daily workout regimen.

“We started with 30 minutes of high-intensity interval training and an hour of weights, seven days per week,” says Fisher. “Then we went to 45-minutes of cardio and two hours of high-intensity interval training, plus weights. I ate oatmeal and egg whites for breakfast. I soon put in 10 hours a day, with five hours of cardio. I drank amino acids and glutamine to keep my muscles from breaking down.”

People who had bet against Fisher proclaimed that he had no shot. One guy flatly said, “You’ll probably look better at the end of all this, but there is no way in hell you’ll win the money.” Fisher did his best to ignore them.

“The money kept him going,” says DiVecchio, who put Fisher through various grueling workouts. “I had him swinging with a weighted hammer; that pushed his heart rate up while working his core. There was boxing, workouts with a medicine ball, cycling, rowing, weights.”

After three months, Fisher’s fat-percentage dipped to 13.5 percent. It was spectacular — but not yet a bet-winning number. Taunts intensified and his backers had added a second wager: They got 4-1 odds on a $50,000 bet that he would drop below 10 percent body fat in just four months. Fisher did everything possible to get there — and lost.

His backers took the initial loss in stride, but Fisher “freaked out” and started doubting himself. He feared he would lose the main bet. That was when DiVecchio called in his mentor Phil Goglia, a sports-medicine nutritionist who has worked with Carmelo Anthony, Christian Bale and Matthew McConaughey.

It turned out that in Goglia’s opinion, Fisher was eating too little. “Walter was taking in just 1,100 calories — not enough to burn caloric heat,” says Goglia. “He was burning muscle when he should have been burning fat.”

Every week, based on Fisher’s lipid profile from bloodwork, Goglia changed his diet.

The approach included “carbohydrate cycling,” strategically incorporating white rice into his meals of protein and vegetables. “It teaches the body to use fat more effectively,” says Goglia. Among his quirkier diet hacks was having Fisher consume a spoonful of iron-rich blackstrap molasses after his last training session of the day. “It shuttles oxygen to red blood cells,” Goglia says. “You wake up with more endurance capacity.” Then there was the water: “Drink one ounce for every pound you weigh. Water is a thermostat. If your body gets low on water, it starts hoarding fat for insulation.”

Nutritional strategies aside, Goglia acknowledges that for the average person, this plan is too extreme. “Unless you’re a pro triathlete, you should not do it,” he says. “But Walter was eating enough to promote caloric support and tissue repair. Taking in 3,200 to 6,000 calories per day, he utilized fat effectively and kept from burning muscle. It was an extreme six months for him.”

With Fisher’s eating plan locked in, DiVecchio kicked up the exercise routine with a machine called the VO2 Max, which is basically a souped-up treadmill or exercise bike that measures the utilization of oxygen. The VO2 Max’s results aided the team in figuring out Fisher’s optimal heart rate for burning fat.

“We kept him at 145 beats per minute for an hour at a time,” says DiVecchio. “He would do five one-hour cardio sessions, plus 75-minutes of weight lifting, then take a 50- to 60-minute break. His legs burned out and we sent him to cryotherapy sessions to speed up recovery.”

Hurtling toward the homestretch, Fisher was focused. “I ate, trained or rested,” he says. “That’s all I did. Fat melted off. They upped my calories and the intensity of my cardio. I ate a ton of tilapia — it’s got high protein, low fat, high omegas. It’s bodybuilder food.”

On June 22, Fisher faced his moment of truth. He lay on an X-ray bed at BodySpec, a medical diagnostic center in Los Angeles, as a bone-density scanner measured his body fat. A technician calculated the results and Fisher looked over his shoulder. Seeing the number come in at a bet-winning 8.8, Fisher — who now weighed 175 pounds — jumped in the air, slapped out high-fives and bear-hugged DiVecchio.

That night, he celebrated the 70-pound weight-loss win — which netted him a little more than $7,000 for every pound lost — by dining solo on four slices of pizza, one with pepperoni.

“He was able to afford it,” says DiVecchio. “He’s since put on a little bit of size. Now we’re focusing on building more muscle mass. This is where it gets to be fun.”

Fisher, who plans to continue staying fit under the tutelage of DiVecchio, would like to keep his weight between 195 and 205 pounds, with body fat at around 13 percent. Debts paid, bankroll replenished, six-pack evident and women finding him more attractive than ever, Fisher, who is single, is understandably confident.

“To have gone from an absolute low to where I am now is an achievement and a transformation,” he says. “A lot of people talk big games — and 99 percent of them would not be able to do what I did, even with the money as an incentive — but I backed it up. I backed it up and it makes me feel like there is absolutely nothing I can’t do.”