Losing weight without dieting sounds like some Harry Potter nonsense. But physician Michael Greger, author of the best-selling health book “How Not To Die” and founder of the myth-busting Web site NutritionFacts.org, says it’s absolutely doable — with science, not magic.

“I hate diet books,” writes the doctor in his new weight-loss book, “How Not To Diet: The Groundbreaking Science of Healthy, Permanent Weight Loss” (Flatiron Books, Dec. 10).

Also on his “hate” list: “pseudoscientific twaddle,” “before-and-after photos,” “filler,” “fantasy” and, heaven forbid, “fluff.”

“You don’t need anecdotes when you have evidence,” Greger says. And he has plenty. His nearly 600-page anti-diet book (a slim volume, it’s not) distills thousands of studies and sources into what Greger calls a “novel weight loss strategy” based on “the best available evidence.”

“The biggest myth is that you have to eat less to lose weight,” Greger tells The Post. “‘Eat less, move more’ is the standard advice you hear, because supposedly a calorie is a calorie . . . but 100 calories from Chiclets is different from 100 calories of chicken or 100 calories of chickpeas. It’s about what your body absorbs.”

For Greger’s tips to work, you have to eat reasonably well to start, and that means lots of whole foods and plants, including beans, greens, nuts, whole grains and berries. (Here are 10 lifesaving foods the vegan doctor thinks you should eat every day.)

But once you have a healthy baseline, there are little tricks you can use to boost your weight loss.

Try these five science-backed tweaks at every meal, Greger says, and the weight should start to drop off naturally — without any cabbage-soup-keto-cleanse craziness.

‘Simply drinking a tall glass of water … [could] wipe out nearly 100 extra calories.’

Wet your palate

Maybe this will inspire you to fill up your Swell bottle: Water is a natural metabolism booster, and it works so well that “simply drinking a tall glass of water four times throughout the day [could] wipe out nearly 100 extra calories,” writes Greger.

Even better if it’s cold water — which has an additional metabolism-boosting potential — as you sip, your body has to work to bring the liquid to body temperature.

When you drink matters, too, because water has a “stomach-filling effect,” writes Greger. To best take advantage of all these benefits, chug two glasses of cold water before every meal.

Choose smarter starters

Your first bites can make or break a meal, says Greger — and the right ones “can effectively subtract 100 calories out of our diet.”

Research backs him up: In one study he cites, scientists served people 900-calorie plates of pasta — some with a starter salad made with water-rich veggies (lettuce, carrots, cucumbers, etc.), some without. The salad-eaters ultimately ate 200 fewer calories of pasta.

In a similar study, people who ate a large apple before a pasta meal — an “apple-tizer,” Greger quips — ate 300 fewer calories.

But it only works if you don’t junk up the app. Desecrating a salad with fatty dressing and tons of cheese is “like preloading a pizza with garlic bread,” writes Greger.

But if you start each meal with an apple, a clean salad or a cup of veggie-based soup (aim for 100 calories per cup and skip the creamy stuff), you’re setting yourself up for success.

Be a vin-ner

Vinegar, and especially apple cider vinegar, has gotten some buzz as a weight-loss miracle. Greger wouldn’t go that far, but he is impressed with how the sour stuff helps to stabilize blood-sugar levels.

“Vinegar has been used medicinally since antiquity,” he writes. In fact, before the advent of blood-sugar medications, “vinegar was used as a folk remedy for diabetes.”

For weight-loss purposes, that’s important because yo-yoing blood sugar levels are what trigger you to abandon daylong healthy habits for a 3 p.m. doughnut binge.

But don’t rip shots of vinegar, as recommended by many a fitness blogger. Instead, “flavor meals or dress a side salad with any of the sweet and savory vinegars out there,” Greger says. He suggests balsamic, sherry, white wine, champagne and, sure, apple cider, if you like. Have two tablespoons with every meal.

Focus on food

This one’s easy: Go screen-free for meals.

“Don’t eat while watching TV or playing with your phone,” writes Greger. Why? Because distraction drives us to eat more, according to several studies he details in his book.

One found that men and women who ate while watching TV averaged an extra slice of pizza or 71% more mac ‘n’ cheese than their screen-free counterparts. A similar study had people eat ice cream while listening to the radio; they ate up to 77% more of the sweet stuff than those who spooned in silence.

Go slow

Yeah, everyone’s busy. But if you can carve out 20 minutes for every meal, you might carve out your waistline, too.

“Studies have demonstrated that no matter how we boost the amount of time [that] food is in our mouths, it can result in lower caloric intake,” writes Greger.

Spending 20 minutes on each meal, he explains, allows “your natural satiety signals” — that mind-body feeling of fullness — “to take full effect.”

It sounds tedious, but if you’re following Greger’s other tips (water, healthy apps), you’re already well on your way. To draw out your actual meal, you can try taking smaller bites, chewing your food for longer or even filling your plate with food that naturally takes longer to eat. Have you ever tried to speed-eat a kale salad? Impossible.