Stop us if you’ve heard this before, but everything you know about weight loss may be wrong.

In his new book, “The Obesity Code: Unlocking the Secrets of Weight Loss,” Dr. Jason Fung, a Toronto-based nephrologist, lays out a radical new approach to diet.

The bottom line: We’ve spent too much time focusing on how much to eat and too little time pondering whether to eat at all.

One of Fung’s most important recommendations involves fasting.

He instructs patients to skip eating for two non-consecutive 24-hour periods in a week, drinking only water, green tea, coffee and broth during those fast days.

Depriving the body of food for an extended period causes it to burn fat more efficiently, he says.

“Instead of searching for some exotic, never-seen-before diet miracle … let’s instead focus on a tried-and-true healing tradition,” writes Fung, who is chief of medicine at a Canadian hospital and a diabetes expert with a yearlong waitlist.

When we eat regularly, he says, our digestive system breaks down the food, glucose is released into the bloodstream, and the glucose is used for fuel.

Some six to 24 hours after not eating anything, however, we begin burning the excess glucose, called glycogen, stored in the liver. Once that’s gone, fat gets burned.

We assume that dropping a dress size is about decreasing the amount eaten in a day, but according to Fung, that’s not the answer. If you decrease what you eat by, say, 200 calories a day, your body will compensate by burning 200 fewer calories.

“Those Hollywood stars, I’m sure they fast all the time but they don’t want to say it because it’s taboo,” Fung tells The Post. Celebs including Hugh Jackman, Miranda Kerr and Jimmy Kimmel have all sung the praises of not eating for a certain time period.

Contrary to what we might think, fasting isn’t dangerous, according to Fung.

“There’s nothing wrong with it,” he says. “It’s 100 percent natural. That’s the way that people have been [eating] for thousands of years.”

One myth is that the body will start eating muscle. Not true, says Fung, and a study in which subjects fasted on alternate days for 70 days found a 6 percent decrease in body mass but an 11.4 percent drop in body fat. Muscle mass didn’t change.

Our bodies adapted to dip into our fat deposits to survive.

Another myth is that not eating will kill energy levels.

“Your basal metabolic rate goes up [while fasting],” Fung says. “In the caveman days, as soon as you had nothing to eat, the body would give us more energy. The body revs up metabolically.”

Not eating might also make you mentally sharper, as it allows blood to be made available to the brain that might otherwise be kept busy digesting a Big Mac.

Fasting also lowers blood sugar and can help prevent diabetes by better controlling insulin, the fat-regulating hormone. Ultimately, Fung argues that obesity is not really about calories — but hormones.

“This finding is the missing piece in the weight-loss puzzle,” Fung writes in the book.

Americans are no doubt hungry for that.

Want to give it a try? Here are Fung’s recommendations:

▪ Try to fast twice a week. If you feel skipping food may be psychologically difficult, eat dinner one night, then opt out of breakfast and lunch the next day. This schedule will allow you to eat something every day, while still abstaining for a full 24 hours.

▪ During the fast, stick to green tea [below], water and coffee. Try to consume 2 liters of water, feeling free to add a squeeze of lemon or a little apple cider vinegar for flavor.

▪ A cup of bone broth is also permitted, and will replenish the salt your body loses while not eating. (Lack of salt can lead to headaches.) You can also drink sparkling water instead of still H2O.

▪ If you get hungry, don’t worry. Hunger comes in waves, and the feeling will pass. Try to stay busy.

▪ Keep your fasting to yourself. Others might try to discourage you, thinking the behavior is radical.

▪ Break the fast with a sensible dinner. Think grilled chicken and green beans. Don’t try to stuff your face with all the calories you missed at once.

▪ Your first fast will be tough, but Fung insists it gets easier as your body adapts. Two or three weeks in, you may feel cheery enough to not be tempted to punch that person eating a bagel in front of you.

Skipping meals is all the rage — here are four more plans to choose from:

Leangains — The diet, developed by personal trainer Martin Berkhan, involves skipping food every day for 14 to 16 hours, going from dinner the previous night to lunch the next day without eating, for example.

Eat Stop Eat — Author Brad Pilon has a similar approach to Fung’s: Cut out all food for one or two non-consecutive 24-hour periods per week. You can go from dinner to dinner, if you like, drinking only water, coffee and tea.

5:2 — For five days of the week, you eat normally, but for two other non-consecutive days, you restrict your intake to just two meals of about 250 calories each. Celebs, including Beyoncé, have sung its praises.

Warrior Diet — Can’t stomach the thought of not eating? The plan from author Ori Hofmekler calls for restricting your calories during the day to just fruit and vegetables, and then having one large meal at night.