Why you shouldn't believe every before-and-after weight loss photo you see.

Image: Sophie Kay/Fitology

It’s a rare feat these days to scroll through Facebook without seeing a before-and-after weight loss photo beaming back at you.

You know the ones — on the left, there’s a young man or woman standing in their bathroom in swimmers, staring solemnly down the lens; on the right, that same person is 5kg lighter and striking a confident pose.

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It’s hard not to buy into the hype these photos create; they make weight loss look achievable and even easy. However, it’s becoming increasingly clear many of these before-and-after photos are a straight-up lie.

For instance, look at the two photos above and take a guess at how much time had elapsed between them. Three weeks? Two months? A year?

In fact, these photos were taken just three minutes apart.

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“All I did in the 3 minutes between the two photos was to turn off the overhead light, put on underwear that fit better, twist my body slightly to the side to show off my best angle, flex and, of course, add a filter," explains personal trainer Sophie Kay, the woman pictured, on her website Fitology.

“Even I have been guilty of only posting the most flattering selfies but don’t trust what you see." (Post continues after gallery.)

Kay's little experiment has gone viral this week, for good reason, but she's not the first woman to illustrate just how deceptive these images can be.

A couple of years ago, the website FastCo produced an infographic detailing the various techniques people use to fake these weight loss images. Clothing choice and personal grooming was a big factor for both women and men, while doing a few pushups between the two photos made a dramatic difference in how men's torsos looked.

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Inspired by this, health and fitness writer Natalia Hawk decided to try her hand at a faux before-and-after to see how easy it really was. The result was pretty telling:

Nat detailed the process for The Glow:

"I waited for a day when I was feeling super bloated. I removed all traces of make-up and fake tan. I put on a pair of bikini bottoms that are two sizes too small, purchased in 2007, that I’ve been holding onto for whatever reasons. I put on an unflattering sports bra, popped my hair up, frowned, stood in the most unflattering position known to humankind and then pushed my stomach out as far as possible.

"The after photo was taken about five minutes later. In that five minutes, I changed my bikini to one that actually fitted and was relatively flattering, slathered myself in fake tan, let my hair out and smiled. Oh – and I fixed my posture, too. That definitely helped."

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What makes all this even scarier is that Sophie Kay and Nat Hawk both could have taken their photos a little further with help from Photoshop and lighting adjustments — this is another deceptive trick common in these photos.

That's not to say every before-and-after photo you see isn't genuine. Many are, and they're shared with perfectly decent intentions — to encourage other people to adopt a healthy lifestyle, or to document their progress.

But when some people are faking these images to sell diet programs and substances that are dubious at best and dangerous at worst, they're insidiously targeting the trust and vulerability of people looking for ways to manage their weight.

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There are two morals to this story:

1. Some people out there are opportunistic jerks.

2. Next time one of these images pops up on your Newsfeed, just keep scrolling. Studying them won't help any of us.

Do you see these photos on Facebook? How do they make you feel?