ALWAYS dieting – still fat?

Maybe there’s not enough fat in your diet.

That’s the thinking behind “The Fat Fallacy,” a book that contends you can have your brie and eat it – and be thinner because of it.

Inspired by two years of living in France, “Fallacy” author Will Clower, a neurophysiologist at the University of Pittsburgh, believes the secret to staying slender and healthy is to embrace fats and shun sugar.

“On one side of the ocean, 281 million Americans have been playing by the low-fat rules all these years and getting fatter,” he writes.

“All the while . . . 58 million French people nonchalantly spend their lives loving their food without our neurotic obsessions, without our obesity problems.”

To add insult to obesity, he points out, the French live longer than we do, too – three years longer, on average, for men.

The secret, Clower says, is that the French savor their food. They eat more slowly, giving their stomachs a chance to recognize that they’re full.

Their full-fat cheeses and yogurt, buttery croissants and meaty cassoulets satisfy them, so they tend to eat smaller portions.

And if they do snack, they’re more likely to reach for a piece of fresh fruit or a piece of cheese than Cheez-its and a Coke. (Not for nothing does “Fat Fallacy” have an endorsement from Julia Child.)

But not all fats are good for you. Clower says the French rarely eat red meat; most of their protein comes from fish, chicken and lean pork.

“The best foods” are anything without a label – fresh-baked, fruit, chicken.

The enemy is anything with partially hydrogenated oil, high-fructose corn syrup, dyes and any additives that sound like the chemicals they are.

Fill your fridge with fresh vegetables and fruit, salmon, pork chops and catfish (and the occasional rump roast).

Overall, Clower offers sound – if not entirely new – advice, says Keith Ayoob, a registered dietitian and associate professor at the Albert Einstein School of Medicine in The Bronx.

But to genuinely eat like the French – and enjoy all the benefits – you must eat smaller portions.

“The French don’t sit down and devour an 8-ounce wheel of brie,” Ayoob says.