I just don't buy the myth that fat people get to have less sex than skinny people - at least not the ones with good old, regular, common-or-garden fat.

Nearly two thirds of us are overweight or obese yet we seem to be finding mates and reproducing somehow. We can no longer tell who's unhealthily fat, making conscious prejudice a challenge. And people claim that men prefer to date skinny - or at least normal weight - but what if they're not so sleek and slender themselves? We're genuinely drawn to people who form a physical attractiveness match (and I'm told that a voluptuous hourglass figure more than makes up for a little fleshy overspill).

What does seem to be true is that if you're very overweight, losing some pounds can significantly improve the quality of your sex life. After gastric bypass - a surgery which decreases your stomach size and reroutes your gut - obese men experience a rise in sexual desire and an increase in sexual performance. This is partly due to hormonal changes - fat is an active organ and if you remove it you stop it pumping out chemicals which mess with sex steroids like testosterone. But losing weight also has psychological effects: a hit of confidence and self-esteem can really get your juices flowing.

Sadly, shedding your excess weight doesn't guarantee your ticket to sexual bliss. Obesity surgery is not a cure-all and some patients feel disappointed. The fat disappears but often the skin around it doesn't, leaving less-than-attractive flaps. The problems of life still remain, and can no longer be blamed on weight. And successful surgery can even break up marriages, by changing relationship dynamics and opening eyes.

Of course if you want to sharpen up your love life you don't have to go under the surgeon's knife. Losing just 10% of your body weight is enough to improve physical health and give yourself a feel-good boost. Research shows that despite the emaciated look of several infamous fashion-savvy starlets, real women are too smart to aspire to be anywhere near that skinny. Keeping a little chubbiness round the cheekbones can actually help you look healthy and young. And if you're really big don't think you have to shrink to half your size: 56% of gastric bypass patients in one study reported improvements in their sexual relationships even when they were still obese post-operation.

The message for Psychology Today's female readership? Losing a bit of excess fleshiness is great for your sex life, especially if it makes you feel self-confident and happy. But when you chuck out the Cheetos and stop super-sizing your fries - don't forget to keep an eye on your sexual partner's portions too.

Happy Valentine's Day everybody.

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