Instagrammer Proves Weight Is Just a Number with Very Different Photos of Her Body at 125 Lbs.

Want proof that weight is just a number? Then look to Arielle Mandelson's Instagram, where she showed how drastically she can tone her body with nutrition and exercise, all while keeping her weight exactly the same.

Mandelson, a behavioral health consultant from Los Angeles, shared a series of three photos of herself over the last two years while she was following different diet plans and exercise routines. In the first photo, taken in Feb. 2016, she thought she was doing everything right after recovering from a near-deadly addiction to drugs and alcohol. But, she says, she still wasn't feeling healthy.

"I spent a year focusing on my emotional well-being before I addressed my physical health, and when I finally did I was so misguided," Mandelson, 32, tells PEOPLE. "I thought 'healthy' meant lean with abs so that's what I pursued, and by all the wrong measures. I all but completely cut carbohydrates out of my diet, ate about twice the protein someone my size should, did a lot of cardio and attempted some random weight exercises. I felt aimless, bloated, lethargic and just completely frustrated."

Looking to make a change, she decided to try out Kayla Itsines' Beach Body Guide program after seeing other women on Instagram have success with the workouts.

"After a few weeks of doing BBG, something inside me had shifted; I could feel myself getting stronger each time I did a workout and my relationship with food improved," Mandelson says. "My motivation was still primarily aesthetically driven but I also wanted to get stronger, so I looked at food as fuel and workouts as personal challenges to overcome. Carbohydrates and I became friends again, and I began exercising in the gym. I craved working out for the first time in my life."

She took the second photo in the set a few months later, after finishing a full round of BBG. "I felt good on the inside, so I liked what I saw in the mirror," Mandelson says.

As she started toning up, Mandelson says she was initially "obsessed" with the number on the scale.

"I thought if I could just get it lower and be a certain weight that I would feel better about myself," she says. "It was disconcerting when the number didn't change at first but my clothes fit better and I felt so good that I was able to ignore it."

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And when her weight wouldn't budge, despite her workouts, Mandelson realized that it was muscle weight.

"Progress photos, vain as they are, became my primary barometer — and they are a much more effective tool for gauging where I was physically," she says.

The third photo is current, and Mandelson says she feels "strong, energetic and proud." She still does BBG, along with other workout programs, and started tracking her macronutrients.

"During the week I eat planned meals that I prepare — and it's way more food than you would believe! — and during the weekend I just eat intuitively," she says. "But I am not stringent about anything; I think people assume I eat leaves all day but really I'm over here eating three desserts after dinner."

And Mandelson says her photos make an important point against focusing on weight.

"Scales can't differentiate between muscle, fat, bones, tissue and water," she says. "There are more accurate ways to measure body composition and that is ultimately what is important. I get messages everyday from women all over the world of all ages asking how to lose weight. It makes me sad to know how much value people give that number, and how much it can control somebody. I know because I've been there."