A fitness star posted before-and-after pictures of herself to prove that weight is just a number

An Instagram exercise star recently posted side-by-side pictures of herself taken three years apart, to show that a person's weight isn't reflective of their fitness level.

Dutch fitness trainer Yola, who has 82,000 followers on Instagram, wrote that in the three years since she had taken the first picture (on the left), she had gained six kilos (13 lbs). But in the recent picture (on the right), she actually looks far more fit.

"I was scrolling back in my phone and found this 'old' (non-flexed) picture. Weight is just a number," Yola wrote in the caption.

Three years ago, Yola was definitely slim, but clearly a bit out of shape, even though she weighed just 58 kilos, or 127 lbs. 

And now, she's got a killer six pack, incredibly toned arms and legs, and looks even more slim - except now she weighs 64 kilos, or 141 lbs.

That's because while fat and muscle weigh the same, muscle is more dense and distributed differently on a person's body.

So, a person who works out a ton could be losing inches from their waistline, but actually gaining pounds on the scale.