It happens every time — just when you’ve had a few too many salty fries and you are left feeling uncomfortably bloated and blimp-like, your man wants to get it on.

What’s a gal to do? Say “yes” but try to keep her Spanx on during sex? Put the kibosh on the whole carnal idea? Stop eating fries forever (because when are men not in the mood)?

These questions are common and, according to sex columnist Michael Alvear, author of Not Tonight Dear, I Feel Fat: How to Stop Worrying About Your Body and Have Great Sex, 50 percent of women have them, too. In fact, chances are you have turned down sex because you were having a fat day.

It’s sad because sex is fun, and what’s more? You are wrong about your body size. Oh yes. You, too.

According to an Ohio State University study, women consistently overestimate their body size — often by as much as 25 percent — and they also vastly overestimate how thin men want them to be!

Regardless of how much they weigh, however, women with a negative body image report much lower levels of sexual arousal than those with positive self judgments, according to research out of Rutgers University. In other words, if you can shift your focus away from your bod and towards the boudoir, you might have a better chance of actually enjoying sex whether your skinny jeans fit or not.

With that in mind, Alvear offers the following five tips for getting in the mood now, in spite of your fat-day funk:

1. Practice makes perfect. The single best way to feel better about your body is to feel good about what it can do. According to Alvear, 67 percent of women report that good sexual experiences contribute to positive body image. In other words, sexual competence = sexual confidence. So just do it. Literally. Tell yourself that you’ll just “go for it” anyway, and chances are two minutes into making out, you’ll forget what you were stressing about anyway.

Take the focus off your body and instead put it on pleasure (yours and his). Then later on, you can laugh at yourself for almost giving up the chance to have sex just because you weren’t feeling body confident. Remember, there are lots of skinny single gals starving for sex … you just got some and they didn’t!

2. Fantasize first. Time to let your imagination run wild since apparently just imagining a positive sexual encounter has been shown to raise a woman’s testosterone levels — and therefore libido.

“Fantasies are simply dressed-up sexual thoughts, which studies have shown elevate testosterone, which is crucial to sexual functioning for women,” says Alvear. “Women ordinarily don’t need a whole lot of help creating sexual fantasies because they tend to be naturally good at it.”

Still, there are ways to jump-start the process. The easiest is to pick out a hot sex scene in a movie or a book you like and mentally pretend you’re one of the characters.

3. Develop erotic cues. “An erotic cue is basically anything that makes your pulse race sexually … it is different things for different women,” says Alvear. “The main thing to watch out for in discovering your erotic cues is subtlety … you’re looking for a flicker, not a flame.”

Start noticing things that turn you on and record them in a journal, whether it’s lots of kissing or brand new office products/school supplies (seriously, that does it for some people … possibly speaking from experience here). Then when you’re having a fat day and not in a randy mood, check out your list and surround yourself with sexy triggers!

4. Exercise — but not to lose weight. Working out for 20 minutes at 70 percent of your heart rate prepares the body for sex, circulating blood faster and raising key hormones like testosterone and oxytocin.

“It’s important to realize that this type of exercise doesn’t ‘make you horny’ but it sets the stage for desire to flourish,” Alvear says. “You still need an erotic cue — like your partner wearing your favorite aftershave — to ignite the ‘desire potential’ that working out creates.”

That said, if you’re having a fat day, getting on a treadmill or stationary bike is not a bad idea if you think sex is in your future plans. Can’t hurt to stoke the fire, right?

5. Be playful.  Making sex fun takes the focus off your body image and makes it more about the enjoyment of it. If you’re not in the mood because you’re having a self-perceived fat day, Alvear recommends trying sex blindfolded … both partners. Not only will the experience allow you to “hide” what is bothering you since your partner cannot see you (taking away some of your insecurities), but the fumbling and extra touching will also add levity and heightened sensuality to the big event!

The Stir